NASA Contractor Report CR-2005-212563 

Severe Weather Forecast Decision Aid 

Prepared By: 

The Applied Meteorology Unit 

Prepared for: 

Kennedy Space Center 

Under Contract NAS10-01052 

NASA 

National Aeronautics and 

Space Administration 

Office of Management 

Scientific and Technical 

Information Program 

2005 
Attributes and Acknowledgments 

NASA/KSC POC: 

Dr. Francis J. Merceret 

YA-D 

Applied Meteorology Unit (AMU) / ENSCO Inc. 

William H. Bauman III 

Mark M. Wheeler 

David A. Short

ii
Executive Summary 

This report presents a 15-year climatological study of severe weather events and related severe weather 

atmospheric parameters. Data sources included local forecast rules, archived sounding data, Cloud-to-Ground 

Lightning Surveillance System (CGLSS) data, surface and upper air maps, and two severe weather event databases 

covering east-central Florida. The local forecast rules were used to set threat assessment thresholds for stability 

parameters that were derived from the sounding data. The severe weather events databases were used to identify

days with reported severe weather and the CGLSS data was used to differentiate between lightning and nonlightning days. These data sets provided the foundation for analyzing the stability parameters and synoptic patterns

that were used to develop an objective tool to aid in forecasting severe weather events. The period of record for the

analysis was May – September, 1989 – 2003. 

The results indicate that there are certain synoptic patterns more prevalent on days with severe weather and

some of the stability parameters are better predictors of severe weather days based on locally tuned threat values. 

The results also revealed the stability parameters that did not display any skill related to severe weather days. 

An interactive web-based Severe Weather Decision Aid was developed to assist the duty forecaster by

providing a level of objective guidance based on the analysis of the stability parameters, CGLSS data, and synopticscale dynamics. The tool will be tested and evaluated during the 2005 warm season.

iii
Table of Contents 

Executive Summary.............................................................................................................................................. iii

List of Figures........................................................................................................................................................vi

List of Tables.........................................................................................................................................................ix

List of Tables.........................................................................................................................................................ix

1. Introduction .....................................................................................................................................................1

2. Data Methodology...........................................................................................................................................2

2.1 Local Forecast Rules...............................................................................................................................2

2.2 Severe Weather Events...........................................................................................................................2

2.3 CGLSS....................................................................................................................................................6

2.4 Synoptic Weather Patterns......................................................................................................................9

2.5 Sounding Stability Parameters..............................................................................................................10

3. Data Analysis Results....................................................................................................................................12

3.1 Stability Parameters..............................................................................................................................12

3.1.1 Total Totals..............................................................................................................................12

3.1.2 K-Index ....................................................................................................................................13

3.1.3 Lifted Index..............................................................................................................................14

3.1.4 Thompson Index ......................................................................................................................15

3.1.5 SWEAT....................................................................................................................................16

3.1.6 Precipitable Water....................................................................................................................17

3.1.7 Showalter Stability Index.........................................................................................................18

3.1.8 Cross Totals .............................................................................................................................19

3.1.9 CAPE .......................................................................................................................................20

3.1.10 CAPE Max θe...........................................................................................................................21

3.1.11 CAPE FMaxT ..........................................................................................................................22

3.1.12 500 mb Temperature ................................................................................................................23

iv
3.1.13 Helicity.....................................................................................................................................24

3.1.14 Summary of Stability Parameters.............................................................................................26

3.2 Synoptic Weather Patterns....................................................................................................................28

3.2.1 250 mb Jet Position..................................................................................................................29

3.2.2 Surface High Pressure Ridge Position .....................................................................................30

3.3 Development of a Severe Weather Decision Aid..................................................................................31

4. Summary .......................................................................................................................................................36

References ............................................................................................................................................................37

List of Abbreviations and Acronyms....................................................................................................................38

Appendix A – 45 WS Severe Weather Worksheet ...............................................................................................39

Appendix B – Jacksonville, Florida NWS Severe Weather Checklist..................................................................40

v
List of Figures 

Figure 1. Map of Florida showing the six counties (shaded in yellow) included in the severe weather

events database. The location of KSC and CCAFS are shown on the map and both reside in

Brevard County. ................................................................................................................................3

Figure 2. Screen capture from the SPC SeverePlot graphical database program. All reports of tornadoes,

hail ≥ 0.75 inches and convective surface winds ≥ 50 knots from 5/1/89 – 10/1/03 over central

Florida are shown. Tornadoes are represented by the red dots, tornado tracks by the red lines, 

hail by the green dots, and convective wind events by the blue plus signs. ......................................3

Figure 3. Locations of all tornado, wind, and hail events in the database used for this task. Tornadoes 

are represented by the red dots, tornado tracks by the red lines, hail by the green triangles, and 

wind events by the red severe thunderstorm symbols. ......................................................................4

Figure 4. Interstate highways (thick black lines) and major roads (thin black lines) superimposed on the 

severe weather events map................................................................................................................5

Figure 5. The locations of the six CGLSS sensors in the network during the period of record for the data

in this task (1989 – 2003) are indicated by the blue octagons. The names of each location are

next to the octagon. In early 2004, the Duda site was moved to Deseret which is shown as a

red octagon. The blue box represents the boundary of the coverage of CGLSS data and is

about 2° x 2° latitude/longitude centered on KSC.............................................................................6

Figure 6. Example of a CGLSS plot from 6 August 1994. Each red dot represents one lightning strike as

observed by the CGLSS. ...................................................................................................................7

Figure 7. Examples of CGLSS data showing (a) number and (b) percent of CG lightning strikes by

county and KSC/CCAFS for the 1994 warm season.........................................................................7

Figure 8. Example of CGLSS number of daily CG lightning strikes for the six counties in east central

Florida for the 1994 warm season. ....................................................................................................8

Figure 9. Screen shot of the interactive web based tool used to view CGLSS maps........................................8

Figure 10. Example of a 300 mb upper air chart used to determine flow aloft over east central Florida. ..........9

Figure 11. Example of a surface map used to determine the position of the surface ridge over east central

Florida. The high pressure ridge axis is highlighted by the jagged blue line. .................................10

Figure 12. Stacked column graph of TT value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The 45 WS

threat criteria and thresholds are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................13

Figure 13. Stacked column graph of KI value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The 45 WS

threat criteria and thresholds are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................14

Figure 14. Stacked column graph of LI value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The 45 WS

threat criteria and thresholds are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................15

Figure 15. Stacked column graph of LI value thresholds. Stacked column graph of LI value thresholds. 

The numbers of severe days are in red, lightning days without severe weather in green, and

vi
non-lightning days in blue. The 88th Weather Squadron threat criteria are on the x-axis. The 

cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold

numbers at the top of each column indicate the total number of days in that threat range and 

the numbers within each colored portion of a column indicate the number of days of that type. ...16

Figure 16. Stacked column graph of SWEAT value thresholds. The numbers of severe days are in red, 

lightning days without severe weather in green, and non-lightning days in blue. The modified 

Jacksonville NWS threat criteria are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................17

Figure 17. Stacked column graph of PW value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The local 

forecast rules threat criteria are on the x-axis. The cumulative frequency of occurrence of each 

type of day is shown on the y-axis. The bold numbers at the top of each column indicate the

total number of days in that threat range and the numbers within each colored portion of a

column indicate the number of days of that type. ...........................................................................18

Figure 18. Stacked column graph of SSI value thresholds. The numbers of severe days are in red, 

lightning days without severe weather in green, and non-lightning days in blue. The 45 WS

threat criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is

shown on the y-axis. The bold numbers at the top of each column indicate the total number of 

days in that threat range and the numbers within each colored portion of a column indicate the

number of days of that type.............................................................................................................19

Figure 19. Stacked column graph of CT value thresholds. The numbers of severe days are in red, 

lightning days without severe weather in green, and non-lightning days in blue. The threat

criteria are based on a modified version of the NWS SRH online glossary (NWS SRH 2005)

and are on the x-axis. The cumulative frequency of occurrence of each type of day is shown 

on the y-axis. The bold numbers at the top of each column indicate the total number of days in

that threat range and the numbers within each colored portion of a column indicate the

number of days of that type.............................................................................................................20

Figure 20. Stacked column graph of CAPE value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The 

Jacksonville NWS threat criteria are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................21

Figure 21. Stacked column graph of CAPE Max θe value thresholds. The numbers of severe days are in

red, lightning days without severe weather in green, and non-lightning days in blue. The

Jacksonville NWS threat criteria are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................22

Figure 22. Stacked column graph of CAPE FMaxT value thresholds. The numbers of severe days are in

red, lightning days without severe weather in green, and non-lightning days in blue. The

Jacksonville NWS threat criteria are on the x-axis. The cumulative frequency of occurrence of

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................23

Figure 23. Stacked column graph of T500 value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The 45 WS

threat criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is

shown on the y-axis. The bold numbers at the top of each column indicate the total number of 

vii
days in that threat range and the numbers within each colored portion of a column indicate the

number of days of that type.............................................................................................................24

Figure 24. Stacked column graph of positive helicity value thresholds. The numbers of severe days are in

red, lightning days without severe weather in green, and non-lightning days in blue. The

Melbourne NWS threat criteria are on the x-axis. The cumulative frequency of occurrence of 

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................25

Figure 25. Stacked column graph of negative helicity value thresholds. The numbers of severe days are

in red, lightning days without severe weather in green, and non-lightning days in blue. The

Melbourne NWS threat criteria are on the x-axis. The cumulative frequency of occurrence of 

each type of day is shown on the y-axis. The bold numbers at the top of each column indicate

the total number of days in that threat range and the numbers within each colored portion of a 

column indicate the number of days of that type. ...........................................................................26

Figure 26. Pie charts showing the relationship between severe days and (a) the upper level jet streak 

position and (b) surface ridge position............................................................................................29

Figure 27. Stacked column graph of 250 mb jet streak position categories. The numbers of severe days 

are in red, lightning without severe weather days in green, and non-lightning days in blue. The 

position of the jet streak is on the x-axis. The cumulative frequency of occurrence of each 

type of day is shown on the y-axis. The bold numbers at the top of each column indicate the

total number of days in that threat range and the numbers within each colored portion of a

column indicate the number of days of that type. ...........................................................................30

Figure 28. Stacked column graph of surface high pressure ridge position. The numbers of severe days are 

in red, lightning without severe weather days in green, and non-lightning days in blue. The

position of the surface ridge is on the x-axis. The cumulative frequency of occurrence of each

type of day is shown on the y-axis. The bold numbers at the top of each column indicate the

total number of days in that threat range and the numbers within each colored portion of a

column indicate the number of days of that type. ...........................................................................31

Figure 29. Proposed 45 WS Severe Weather Decision Aid Worksheet GUI. Forecasters will answer each 

item by checking either the “Yes”, “No” or “Not Sure” boxes. The “Total Threat Score” will 

be automatically displayed at the bottom of the worksheet as the forecaster checks boxes............35

viii
List of Tables 

Table 1. Stability parameters and the equations used in their calculation.....................................................11

Table 2. NWS Southern Region Headquarters criteria for Cross Totals east of the Rockies from their 

online glossary. ...............................................................................................................................19

Table 3. Summary of the 8 stability parameters that showed some potential to indicate the severe 

weather chance. The most significant threat category and combined occurrence/severe

occurrence are shaded in light yellow. ............................................................................................27

Table 4. Summary of the 6 stability parameters that did not show potential to indicate the severe 

weather chance................................................................................................................................28

ix
1. Introduction

The 45th Weather Squadron (45 WS) Commander’s morning weather briefing includes an assessment of the

likelihood of local convective severe weather for the day in order to enhance protection of personnel and material 

assets of the 45th Space Wing, Cape Canaveral Air Force Station (CCAFS), and Kennedy Space Center (KSC). The 

severe weather elements produced by thunderstorms include tornadoes, convective surface winds ≥ 50 knots, and/or 

hail with a diameter ≥ 0.75 inches. Forecasting the occurrence and timing of these phenomena is challenging for 45 

WS operational personnel. The AMU has been tasked with the creation of a new severe weather forecast decision 

aid, such as a flow chart or nomogram, to improve the various 45 WS severe weather watches and warnings. The

tool will provide severe weather guidance for the day by 1100 UTC (0700 EDT). 

An Internet, journal article and periodical search was conducted to find and review work done in the area of

forecasting severe weather. Very little current information was discovered or valid for the central Florida region.

Most research has been done on storms in the Midwest or on weather events several decades ago. 

The AMU developed databases for reported severe weather events, synoptic weather patterns associated with

severe and non-severe weather events, and Cloud-to-Ground Lightning Surveillance System (CGLSS) lightning 

data. Current severe weather forecast indices, procedures and/or signatures in east-central Florida (KSC/CCAFS) 

and other similar locales were investigated. Guidelines for stability index thresholds and other severe weather 

thresholds that are locally applicable were explored. Based on the results of the analyses, an interactive web-based 

Severe Weather Decision Aid was developed to assist the duty forecaster by providing a level of objective guidance 

based on the analysis of the morning CCAFS sounding stability parameters, CGLSS data, and synoptic-scale

dynamics. This tool improves upon the original 45 WS Severe Weather Checklist (4.Appendix A) because it is

based on a statistical climatology of 15 year’s worth of data tuned to east-central Florida, it is more objective and it 

is presented in a user-friendly interactive web-based GUI. 

1
2. Data Methodology 

It is important to determine how experienced Florida forecasters have tackled severe weather forecasts – to 

understand what data and rules-of-thumb they use, what triggers are believed important, what parameters are 

specific to Florida severe weather and how all the information is pulled together. Armed with this knowledge, five 

distinct data sets were developed and then merged together. The data sets included local forecast rules, severe 

weather events, cloud-to-ground lightning, synoptic weather patterns, and sounding stability parameters. All five

types of “data” were important to tackle this difficult forecast problem. Each data type has some relevance to 

forecasting the threat of convection in Florida and if evaluated properly could help forecast the threat of severe

weather at KSC/CCAFS. 

2.1 Local Forecast Rules 

The 45 WS provided the AMU with their Severe Weather Worksheet (Appendix A) and numerous forecasters 

discussed their procedures for developing a severe weather forecast. With the exception of the launch weather

officers, most of the 45 WS forecasters have limited experience forecasting at KSC/CCAFS due to the transitory 

nature of military assignments. Forecasters typically stay in one place for about three years which hampers their 

ability to develop their own personal experience in forecasting for the local area. 

Members of the AMU staff visited with three Florida NWS forecast offices to further develop the forecaster

experience database for this task. They visited Melbourne, Jacksonville, and Tampa NWS offices to discuss how 

their forecasters evaluate the probability of severe weather on any particular day. NWS forecasters tend to stay at

one forecast office for many years and develop a keen sense for the local nuances that play a role in severe weather 

forecasting. Of the three offices visited, only Jacksonville had a severe weather checklist (Appendix B) that is used

occasionally by the forecasters. In general, the three NWS forecast offices relied on the knowledge and expertise of 

each individual forecaster. They do not have or utilize any decision aids or checklist. Each forecaster is well trained 

in the local environment and relies on NWS national, regional and local training programs. 

2.2 Severe Weather Events 

Severe weather events included tornadoes, convective surface winds ≥ 50 knots (≥ 26 m s-1), and/or hail with a

diameter ≥ 0.75 inches (≥ 1.9 cm). Severe weather occurrence reports were found in the National Climatic Data

Center (NCDC) U. S. Storm Events Database (NCDC 2004), and from the Storm Prediction Center (SPC) database

(Hart and Janish 2003). Severe weather events from six east central Florida counties were extracted from the NCDC

and SPC databases. Reports from the six counties were needed to make sure the database had enough events to

derive meaningful statistical relationships since so few events occur in the KSC/CCAFS area. Figure 1 shows a map 

of Florida with the six counties highlighted in yellow. There are three coastal counties (Volusia, Brevard, Indian

River) and three inland counties (Seminole, Orange, Osceola), all of which are typically in the same large-scale air 

mass as KSC/CCAFS on most warm season days. The main triggers of convection in the warm season are the 

location, movement, and strength of the local sea breeze front and storm outflow boundary collisions. Two sources

of reported severe weather were used to create the severe weather events database for this task. 

The NCDC database was the primary data source used and contains data from the following:

• Severe weather events from 1993 – 1995 (except 6/93 – 7/93) with no latitude/longitude, and 

• Severe weather events from 1996 – Current including latitude/longitude. 

Additional data from the SPC database include:

• Tornadoes from 1950 – 1992,

• Thunderstorm winds ≥ 50 knots from 1955 – 1992, and 

• Hail ≥ 0.75 inches from 1955 – 1992. 

The NCDC data were cross-checked with the SPC data. The SPC data are available through a graphical 

database developed by SPC called SeverePlot (Hart and Janish 2003). SeverePlot contains data files available from 

1950 – current, updated every July, and allows users to create custom maps showing the locations of tornadoes and

severe hail and wind events (Figure 2). Tabular data can be saved in ASCII format for use in other programs. 

2
Figure 1. Map of Florida showing the six counties (shaded in yellow)

included in the severe weather events database. The location of KSC and

CCAFS are shown on the map and both reside in Brevard County. 

Figure 2. Screen capture from the SPC SeverePlot graphical database program.

All reports of tornadoes, hail ≥ 0.75 inches and convective surface winds ≥ 50 

knots from 5/1/89 – 10/1/03 over central Florida are shown. Tornadoes are 

represented by the red dots, tornado tracks by the red lines, hail by the green 

dots, and convective wind events by the blue plus signs. 

3
The SPC and NCDC databases were merged into one database for this task since both contained some severe 

weather events the other did not have. The final database included only severe weather events in the six east central

Florida counties for 1989 – 2003 and only during the warm season (May – September). The commercial-off-theshelf graphical information system software package ESRI® ArcMapTM was used to display all tornado, hail and 

wind events included in the database used for this task (Figure 3). 

Figure 3.Locations of all tornado, wind, and hail events in the database used for this task. 

Tornadoes are represented by the red dots, tornado tracks by the red lines, hail by the green

triangles, and wind events by the red severe thunderstorm symbols. 

The database contained a total of 635 reported severe weather events of which 40 were tornadoes, 270 hail, and 

325 wind gust. Many of the reports in the database are recorded at the same latitude and longitude resulting in fewer 

than 635 plots in Figure 3. The reason they are recorded at the same latitude and longitude is because the storm data

is entered into the NCDC and SPC databases as a distance in miles and a direction on 16-point compass scale from a 

known location, usually a town or city. For example: 4.5 miles ESE Orlando. The NWS uses a database of over

106,000 cities and towns including their latitudes and longitudes. Using an algorithm, the location 4.5 miles ESE of

Orlando can be derived from the known latitude and longitude of Orlando. These latitude and longitude pairs are 

generated by the NWS and populated into the database (NCDC 2004). 

Of the 635 reported severe weather events, rawinsonde data from the morning (~1000 UTC) sounding at

CCAFS was available for 364 days (some of the days had multiple severe events). The rawinsonde data were 

4
available for 27 tornadoes, 137 hail events, and 200 wind events. It is important to note that the database contains 

only those severe weather events that were reported by human observers (general public, law enforcement, NWS 

spotters, etc.). Severe weather events can only be recorded when observed by people in the vicinity, and then only if 

the proper authorities are notified. Results from a study by the KSC Weather Office (Ward 2004) indicated that

many severe weather events likely go unreported in east central Florida due to low population densities in many

areas of the six-county region. For the 15 year period, for days with a morning CCAFS rawinsonde that could be 

used to compute stability indices, about 82% of all days had lightning observed by the CGLSS in at least one of the 

six counties considered while only 13% of these days had reported severe weather. This does not mean severe 

weather did not occur on the other 87% of the days with lightning, it just was not reported. When interstate

highways and major roads are superimposed on the map from Figure 3 as shown in Figure 4, there is a clear 

correlation between severe weather reports and population/popular roadways. This fact makes the unambiguous

separation of severe weather days from non-severe weather days in the database impossible. Severe weather days are

more accurately described as “reported” severe weather days. However, in order to determine relationships between 

the data and severe weather occurrence, an assumption had to be made that severe weather only occurred on

reported severe weather days. In this work, days with reported severe weather were classified as severe days, days

with CGLSS-observed lightning were classified as lightning days, and days with no CGLSS-observed lightning or

reported severe weather were classified as non-lightning days. 

Figure 4.Interstate highways (thick black lines) and major roads (thin black lines)

superimposed on the severe weather events map. 

5
2.3 CGLSS 

The CGLSS is a lightning detection network of six sensors (Figure 5) that collects date/time, latitude/longitude, 

strength, and polarity information of cloud-to-ground strikes in the local area. The CGLSS data provided to the 

AMU covered a 2° x 2° latitude/longitude area approximately centered at KSC as shown in Figure 5. The CGLSS 

data were required to segregate the days with lightning from days without lightning. Even though the goal of this

task was to increase the objectivity of and improve severe weather forecasts, it became obvious during the synoptic 

pattern and atmospheric stability analyses that it would be difficult to distinguish severe weather days from all other 

days with significant objectivity. It was decided to first determine if there was an objective way to forecast days 

without lightning versus days with lightning, regardless of whether or not a severe weather event was reported. This

was accomplished by first converting the CGLSS data from ASCII format files into dBase IV format files for input

into the commercial-off-the-shelf graphical information system software package ESRI® ArcMapTM. Using this

software, the lightning strikes were plotted on a central Florida map to determine the days that lightning occurred. 

The CGLSS data were plotted for each warm season day. As stated in Section 2.2, if a CG lightning strike occurred 

within one of the six counties, the day was considered a lightning day. An example of a CGLSS plot from 6 August

1994 is shown in Figure 6. 

Figure 5. The locations of the six CGLSS sensors in the network during the period of

record for the data in this task (1989 – 2003) are indicated by the blue octagons. The names of 

each location are next to the octagon. In early 2004, the Duda site was moved to Deseret

which is shown as a red octagon. The blue box represents the boundary of the coverage of

CGLSS data and is about 2° x 2° latitude/longitude centered on KSC. 

6
Figure 6. Example of a CGLSS plot from 6 August 1994. Each red dot represents one

lightning strike as observed by the CGLSS. 

Although not directly part of this task, the CGLSS data were tabulated to produce statistics to include the 

number of lightning days per county and the KSC/CCAFS area, percent of lightning days per county and

KSC/CCAFS area, and daily lightning strikes for all six counties. Examples of the data charts are shown in Figure 7

and Figure 8. The data are available in Excel format on CD-ROM. Additionally, an interactive web-based tool was 

produced for easy interrogation of the CGLSS maps and provided on CD-ROM. A screen shot of the web-based

CGLSS tool is shown in Figure 9. 

1994 Warm Season

Number of Days with Lightning

0

20

40

60

80

100

120

140

IR Brevard Volusia Seminole Orange Osceola KSC/CCAFS

Location a

1994 Warm Season

Percent of Days with Lightning

68% 71% 66% 62%

70% 75%

51%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

IR Brevard Volusia Seminole Orange Osceola KSC/CCAFS

Location b

Figure 7. Examples of CGLSS data showing (a) number and (b) percent of CG lightning strikes by county and

KSC/CCAFS for the 1994 warm season.

7
1994 Warm Season

Daily CG Lightning Strikes

0

2000

4000

6000

8000

10000

12000

14000

5/15/8

5/155/225/29

6/5

6/126/196/26

7/3

7/107/177/247/31

8/7

8/148/218/28

9/4

9/119/189/25

Date

Number of CG Strikes

Figure 8. Example of CGLSS number of daily CG lightning

strikes for the six counties in east central Florida for the 1994 

warm season. 

Figure 9. Screen shot of the interactive web based tool used to view CGLSS maps. 

8
2.4 Synoptic Weather Patterns

The synoptic weather patterns investigated included the position of the upper level jet streak (if any) and 

position of the surface high pressure ridge axis over east central Florida. It is commonly known that upper level

divergence and/or a jet streak exit region in the vicinity of convective systems can help produce severe weather.

Historical upper air charts similar to the example in Figure 10 were evaluated for each day in the 15-year period and 

one of five criteria were entered into the database. The upper level criteria under consideration were:

• Jet streak not present, 

• Jet streak overhead, 

• Jet exit region overhead, 

• Upper level divergence overhead, or

• Jet position undetermined. 

Figure 10. Example of a 300 mb upper air chart used to determine flow aloft over east

central Florida. 

The 45 WS forecasters often analyze the position of the surface high pressure ridge axis protruding westward 

form the Bermuda high pressure center as an indicator for convection occurrence. It is generally accepted that if the

surface ridge is south of the KSC/CCAFS area the chance for convection is increased. Historical surface maps 

similar to that shown in Figure 11 were evaluated for each day in the 15-year period and the position of the surface

high pressure ridge was characterized as 

• No surface high pressure ridge, 

• High pressure ridge north of KSC/CCAFS, or 

• High pressure ridge south of KSC/CCAFS. 

9
Figure 11. Example of a surface map used to determine the position of the

surface ridge over east central Florida. The high pressure ridge axis is

highlighted by the jagged blue line. 

2.5 Sounding Stability Parameters 

A thorough analysis of atmospheric stability based on a local upper air sounding is needed for any convective 

forecast. The 45 WS Severe Weather Worksheet (Appendix A) analyzes four stability indices. 

• Lifted Index (LI), 

• K-Index (KI),

• Total Totals (TT), and

• Showalter Stability Index (SSI). 

These indices are calculated from the 1000 UTC CCAFS rawinsonde via the Meteorological Interactive Data

Display System (MIDDS). These four indices and nine others that are readily available via MIDDS from the

CCAFS rawinsonde were evaluated for each day in the database. They include the 

• Severe Weather Threat Index (SWEAT), 

• Cross Totals (CT), 

• Thompson Index (TI), 

• Convective Available Potential Energy (CAPE), 

• Precipitable Water (PW), 

• Convective Inhibition (CIN), 

• Helicity, 

• CAPE based on Maximum Equivalent Potential Temperature (CAPE Maxθe), and 

• CAPE based on Maximum Forecast Temperature (CAPE FMaxT). 

10
A summary of how each stability index was calculated is shown in Table 1. 

Table 1. Stability parameters and the equations used in their calculation.

Index Units Calculation

LI (T500 – T*) 

T* = Temperature of a parcel characterized by the mean Td in the lowest 3000ft and the 

forecast maximum surface temperature if it were lifted dry adiabatically to saturation and 

then moist adiabatically to 500 mb.

KI (T850 – T500) + Td850 – (T700 – Td700) 

TI KI – LI or [(T850 – T500) + Td850 – (T700 – Td700)] – [(T500 – T*)]

TT (T850 – T500) + (Td850 – T500) 

SSI (T500 – T*) 

T* = Temperature a parcel characterized by the T850 and Td850 would have if it were lifted

dry-adiabatically to the LCL and then moist-adiabatically to 500 mb.

SWEAT 12D + 20 (T-49) + 2F8 + F5 + 125 (S + 0.2)

D = Td850 (if D is negative, then 12D = 0) 

F8 = 850 mb wind speed in knots 

F5 = 500 mb wind speed in knots 

S = sin(500 mb – 850 mb wind direction) 

T = Total Totals (If T is less than 49, the term [20 (T-49)] is set to zero)

CT (Td850 – T500) 

CAPE J/kg ( ) ln EL

LFC

p

p − − R T T d p ∫

R = Universal gas constant 

pEL = Pressure at the equilibrium level 

pLFC = Pressure at the level of free convection 

T = Temperature of the lifted air parcel 

T = Temperature of the environment

CAPE Max θe J/kg CAPE calculated using the layer with the maximum equivalent potential

temperature (θe) 

CAPE FMaxT J/kg CAPE calculated using the forecast maximum temperature for the day 

instead of the surface temperature in the morning 

PW mm Precipitable water in the layer from the surface to 500 mb

CIN J/kg R (T T ) d p LFC

o

p

p

ln ∫ − −

R = Universal gas constant 

pLFC = Pressure at the level of free convection 

po = Pressure at the surface 

T = Temperature of the lifted air parcel 

T = Temperature of the environment

Helicity m2 s

-2 ( ) ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂ − ⋅ × ∫ z

V V C k

km

r r r ˆ 3

0

V

r

= Environmental wind vector 

C

r

= Storm motion vector 

k

ˆ = Unit vector in the vertical 

11
3. Data Analysis Results 

The local forecast rules were used to set threat assessment thresholds for the stability parameters, the severe 

weather events were used to identify days with reported severe weather and the CGLSS data was used to

differentiate between lightning and non-lightning days. These three data sets provided the foundation for analyzing

the stability parameters and synoptic patterns which are discussed in detail in this section. 

3.1 Stability Parameters 

The relationship between each stability parameter and threshold criteria for the severe weather threat was 

calculated for each day-type based on the 1000 UTC CCAFS sounding. The threshold values were provided by one 

of the following sources in order: 

• 45 WS Severe Weather Worksheet, 

• Jacksonville NWS Severe Weather Checklist,

• Forecaster experience, or 

• Other nationally accepted criteria 

The intent was to evaluate if a threshold level could be used as a predictor of severe weather and, if so, if the

threshold value needed to be adjusted for the local KSC/CCAFS area. Stacked column graphs were created and 

statistics calculated to show the relationship between each stability index threshold values and the type of weather 

day. All of the stability parameters and their potential to forecast severe weather are summarized in Table 3 at the

end of Section 3.1.14. 

3.1.1 Total Totals 

The TT thresholds were derived from the 45 WS Severe Weather Worksheet which specifies that there is a low 

threat for severe weather when TT < 45, a medium threat when TT is between 46 and 48, and a high threat when TT 

> 48. These thresholds do not account for TT = 45, so, for this report, it was assumed the low threat would include

TT ≤ 45. Referring to Figure 12, there were 118 days out of 1355 with reported severe weather when the severe

weather threat was low, 107 days out of 591 with reported severe weather when the severe weather threat was

medium and 46 days out of 160 with reported severe weather when the severe weather threat was high. The TT

values were in the low range 64% of the days during the warm season. When there was a low threat, lightning

without severe weather occurred on 67% of the days and severe weather occurred on 9% of the days, leaving 24% of

the days as non-lightning days. Only 8% of warm season days had a TT in the high threat range. But when TT was

in the high range, severe days occurred 29% of the time and non-severe lightning days occurred 68% of the time. 

When the severe weather threat was medium, severe weather days accounted for 18% and non-severe lightning days

75% of the total. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 9% chance of severe weather, 67% chance of lightning without severe weather,

• Medium threat: 18% chance of severe weather, 75% chance of lightning without severe weather, and 

• High threat: 29% chance of severe weather, 68% chance of lightning without severe weather.

12
Total Totals

118

107

46

911

446

108

326

38 6

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (≤ 45) Med (46 to 48) High (> 48)

Threat

Occurrence

Severe Lightning Non-Lightning

1355 591 160

Figure 12. Stacked column graph of TT value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The 45 WS threat criteria 

and thresholds are on the x-axis. The cumulative frequency of occurrence of each type of day is shown 

on the y-axis. The bold numbers at the top of each column indicate the total number of days in that threat 

range and the numbers within each colored portion of a column indicate the number of days of that type. 

3.1.2 K-Index 

The KI thresholds derived from the 45 WS Severe Weather Worksheet indicate that there is a low threat for 

severe weather when KI < 26, a medium threat when KI is between 26 and 28, and a high threat when KI > 28. 

Referring to Figure 13, there were 58 days out of 763 with severe weather when the threat was low, 36 days out of

204 with severe weather when the threat was medium, and 177 days out of 1139 with severe weather when the threat

was high. The KI values were in the low range 36% of the days during the warm season. When there was a low 

threat, lightning without severe weather occurred on 53% of the days and severe weather on 8% of the days.

Therefore, 39% of the days were non-lightning days. When the severe weather threat was medium, severe weather 

days accounted for 18% and lightning without severe weather days for 72% of the total. When the severe weather 

threat was high, severe days occurred 16% of the time and lightning without severe weather days occurred 80% of

the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 8% chance of severe weather, 53% chance of lightning without severe weather,

• Medium threat: 18% chance of severe weather, 72% chance of lightning without severe weather, and 

• High threat: 16% chance of severe weather, 80% chance of lightning without severe weather.

13
K-Index

58

36 177

404

146 915

301

22 47

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (< 26) Med (26 to 28) High (> 28)

Threat

O

ccurren

c

e

Severe Lightning Non-Lightning

763 204 1139

Figure 13. Stacked column graph of KI value thresholds. The numbers of severe days are in red, lightning days

without severe weather in green, and non-lightning days in blue. The 45 WS threat criteria and thresholds are on

the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold numbers 

at the top of each column indicate the total number of days in that threat range and the numbers within each 

colored portion of a column indicate the number of days of that type. 

3.1.3 Lifted Index 

The LI thresholds derived from the 45 WS Severe Weather Worksheet indicate that there is a low threat for 

severe weather when LI > -2, a medium threat when LI is between -3 and -5, and a high threat when LI < -5. These

thresholds do not account for LI = -2, so it was assumed the low threat would be LI ≥ -2. Referring to Figure 14, 

there were 122 days out of 1190 with severe weather when the threat was low, 133 days out of 853 with severe

weather when the threat was medium and 16 days out of 63 with severe weather when the threat was high. The LI

values were in the low range (LI ≥ -2) 57% of the days during the warm season. When there was a low threat, 

lightning without severe weather occurred on 62% of the days and severe weather occurred on 10% of the days. 

Therefore, 28% of the days were non-lightning days. When the severe weather threat was medium, severe weather 

days accounted for 16% and lightning days without severe weather for 80% of the total. The LI value was in the

high threshold range on only 3% of warm season days. When the LI value indicated a high threat, severe days

occurred 25% of the time and lightning days without severe weather occurred 71% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 10% chance of severe weather, 62% chance of lightning without severe weather,

• Medium threat: 16% chance of severe weather, 80% chance of lightning without severe weather, and 

• High threat: 25% chance of severe weather, 71% chance of lightning without severe weather.

14
 Lifted Index

122 133

16

740

680

45

328

40 2

0%

20%

40%

60%

80%

100%

Low (≥ -2) Med (-3 to -5) High (< -5)

Threat

Occurre

nce

Severe Lightning Non-Lightning

1190 853 63

Figure 14. Stacked column graph of LI value thresholds. The numbers of severe days are in red, lightning days

without severe weather in green, and non-lightning days in blue. The 45 WS threat criteria and thresholds are on

the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold numbers 

at the top of each column indicate the total number of days in that threat range and the numbers within each 

colored portion of a column indicate the number of days of that type. 

3.1.4 Thompson Index 

The TI thresholds were derived from the 88th Weather Squadron’s Guide to Thunderstorm Stability Indices

(88th Weather Squadron 2004) which specifies no thunderstorms when TI < 25, possible thunderstorm occurrence 

when TI is between 25 and 34, strong thunderstorms when TI is between 35 and 39, and potentially severe 

thunderstorms when TI ≥ 40. Referring to Figure 15, there were 37 days out of 637 with reported severe weather 

when the threat was low, 125 days out of 758 with reported severe weather when the threat was medium, 84 days

out of 539 with reported severe weather when the threat was high and 25 out of 119 with reported severe weather

when the threat was very high. The TI values were in the low range 31% of the days during the warm season. When

there was a low threat, lightning without severe weather occurred on 48% of the days and severe weather occurred 

on 6% of the days. Therefore, 46% of the days were non-lightning days. When the severe weather threat was

medium, severe weather days accounted for 16% and lightning days without severe weather for 75% of the total. 

When the severe weather threat was high, severe weather days accounted for 16% and lightning days without severe 

weather for 82% of the total. The TI values were at the very high end of the threat range on 6% of warm season

days. When there was a very high threat, severe days occurred 21% and lightning days without severe weather

occurred 79% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 6% chance of severe weather, 48% chance of lightning without severe weather,

• Medium threat: 16% chance of severe weather, 75% chance of lightning without severe weather, 

• High threat: 16% chance of severe weather, 82% chance of lightning without severe weather, and 

• Very high threat: 21% chance of severe weather, 79% chance of lightning without severe weather. 

15
 Thompson Index

37

125 84 25

307

571 440 94

293

62 15 0

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (< 25) Med (25 to 34) High (35 to 39) Very High (> 40)

Threat

O

ccurre

nce

Severe Lightning Non-Lightning

637 758 539 119

Figure 15. Stacked column graph of LI value thresholds. Stacked column graph of LI value thresholds. The

numbers of severe days are in red, lightning days without severe weather in green, and non-lightning days in blue.

The 88th Weather Squadron threat criteria are on the x-axis. The cumulative frequency of occurrence of each type 

of day is shown on the y-axis. The bold numbers at the top of each column indicate the total number of days in

that threat range and the numbers within each colored portion of a column indicate the number of days of that 

type. 

3.1.5 SWEAT 

The SWEAT thresholds were derived from the Jacksonville NWS Severe Weather Checklist which specifies a

low threat when SWEAT < 200, moderate when SWEAT is between 200 and 300, high when SWEAT is between

301 and 400, very high when SWEAT is between 401 and 500, and extreme when SWEAT > 500. There were no

SWEAT values above 400 in the database so the Jacksonville NWS severe weather threat criteria for very high and

extreme were not used, and their moderate threat was named medium here for consistency. Referring to Figure 16, 

there were 165 days out of 633 with severe weather when the threat was low, 91 days out of 1441 with severe

weather when the threat was “medium”, 15 days out of 32 with severe weather when the threat was high. When

there was a low threat, lightning without severe weather occurred on 42% of the days and severe weather occurred 

on 26% of the days. Therefore, 32% of the days were non-lightning days. When the severe weather threat was 

medium, severe weather days accounted for 6% and lightning days without severe weather for 82% of the total. The

SWEAT values were in the high range on only 2% of warm season days. When the SWEAT values were in the high

range, severe days occurred 47% and lightning days without severe weather occurred 47% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 26% chance of severe weather, 42% chance of lightning without severe weather,

• Medium threat: 6% chance of severe weather, 82% chance of lightning without severe weather, and 

• High threat: 47% chance of severe weather, 47% chance of lightning without severe weather.

16
 SWEAT

165

91

15

263 1187

15

205

163 2

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (< 200) Med (200 to 300) High (> 300)

Threat

O

ccurre

nce

Severe Lightning Non-Lightning

633 1441 32

Figure 16. Stacked column graph of SWEAT value thresholds. The numbers of severe days are in red, lightning

days without severe weather in green, and non-lightning days in blue. The modified Jacksonville NWS threat

criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The 

bold numbers at the top of each column indicate the total number of days in that threat range and the numbers 

within each colored portion of a column indicate the number of days of that type. 

3.1.6 Precipitable Water 

The PW thresholds were derived from discussions with the 45 WS. A low threat is generally assumed when PW 

< 1.00 in, medium when PW is between 1.00 in and 1.50 in, and high when PW > 1.50 in. Referring to Figure 17,

there were 3 days out of 90 with severe weather when the threat was low, 54 days out of 585 with severe weather

when the threat was medium and 215 days out of 1431 with severe weather when the threat was high. The PW

values were in the low range 4% of the days during the warm season. When there was a low threat, lightning without

severe weather occurred on 20% of the days and severe weather occurred on 3% of the days. Therefore, 77% of the 

days were non-lightning days. When the severe weather threat was medium, severe weather days accounted for 9% 

and lightning days without severe weather for 53% of the total. The PW values were in the high range on 68% of

warm season days. When PW was high, severe days occurred 15% of the time and lightning days without severe

weather occurred 79% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 3% chance of severe weather, 20% chance of lightning without severe weather,

• Medium threat: 9% chance of severe weather, 53% chance of lightning without severe weather, and 

• High threat: 15% chance of severe weather, 79% chance of lightning without severe weather.

17
 Precipitable Water

3 54 215

18

312

1134

69

219

82

0%

20%

40%

60%

80%

100%

Low (< 1.0) Med (1.0 to 1.5) High (> 1.5)

Threat

O

ccurre

nce

Severe Lightning Non-Lightning

90 585 1431

Figure 17. Stacked column graph of PW value thresholds. The numbers of severe days are in red, lightning days

without severe weather in green, and non-lightning days in blue. The local forecast rules threat criteria are on the 

x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold numbers at 

the top of each column indicate the total number of days in that threat range and the numbers within each colored 

portion of a column indicate the number of days of that type. 

3.1.7 Showalter Stability Index

The SSI thresholds derived from the 45 WS Severe Weather Worksheet indicate that there is a low threat when

SSI ≥ 3, a medium threat when SSI is between 2 and -2, and a high threat when SSI < -2. Referring to Figure 18,

there were 61 days out of 842 with severe weather when the threat was low, 198 days out of 1226 with severe

weather when the threat was medium, 12 days out of 38 with severe weather when threat was high. When there was 

a low threat, lightning without severe weather occurred on 58% of the days and severe weather occurred on 7% of

the days. Therefore, 35% of the days were non-lightning days. When the severe weather threat was medium, severe

weather days accounted for 16% and lightning days without severe weather for 78% of the total. The SSI values

were in the high range on only 2% of warm season days. When SSI was in the high range, severe days occurred 32% 

of the time and lightning days without severe weather occurred 68% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 7% chance of severe weather, 58% chance of lightning without severe weather,

• Medium threat: 16% chance of severe weather, 78% chance of lightning without severe weather, and 

• High threat: 32% chance of severe weather, 68% chance of lightning without severe weather.

18
 Showalter Stability Index

61

198

12

485

954

26

296

74 0

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (≥ 3) Med (2 to -2) High (< -2)

Threat

O

c

c

urrence

Severe Lightning Non-Lightning

842 1226 38

Figure 18. Stacked column graph of SSI value thresholds. The numbers of severe days are in red, lightning days

without severe weather in green, and non-lightning days in blue. The 45 WS threat criteria are on the x-axis. The

cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold numbers at the top of

each column indicate the total number of days in that threat range and the numbers within each colored portion of 

a column indicate the number of days of that type. 

3.1.8 Cross Totals 

The CT thresholds were derived from the threat criteria in the NWS Southern Region Headquarters (SRH)

online glossary (NWS SRH 2005). Table 2 is from the glossary and shows the criteria for CT east of the Rockies. 

Based on the range of CT values in the stability database compared with those in Table 2, the severe threat levels 

were defined as low, medium, high, and very high. The threat level was defined as low when CT ≤ 19, medium

when CT was between 20 and 21, high CT was between 22 and 23, and very high when CT ≥ 24. 

Table 2. NWS Southern Region Headquarters criteria for Cross Totals east

of the Rockies from their online glossary. 

Cross Totals

(CT) Forecast 

18-19 Isolated or few thunderstorms 

20-21 Scattered thunderstorms 

22-23 Scattered thunderstorms, isolated severe 

24-25 Scattered thunderstorms, few severe, isolated tornadoes 

26-29 Scattered to numerous thunderstorms, few to scattered severe, few 

tornadoes 

30 Numerous thunderstorms, scattered severe, scattered tornadoes 

19
Referring to Figure 19, there were 88 days out of 905 with severe weather when the threat was low, 89 days out

of 622 with severe weather when the threat was medium, 61 days out of 457 with severe weather when the threat

was high, and 33 days out of 122 with severe weather when the threat was very high. When there was a low threat,

lightning without severe weather occurred on 61% and severe weather on 10% of the days. When the severe weather 

threat was medium, severe weather days accounted for 14% and lightning days without severe weather for 75% of

the total. When the severe weather threat was high, severe weather days accounted for 13% and lightning days

without severe weather 79% of the total. The CT values were in the very high threat range on only 6% of warm

season days. When CT was very high, severe days occurred 27% and lightning days without severe weather 70% of

the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 10% chance of severe weather, 61% chance of lightning without severe weather,

• Medium threat: 14% chance of severe weather, 75% chance of lightning without severe weather, 

• High threat: 13% chance of severe weather, 79% chance of lightning without severe weather, and 

• Very high threat: 27% chance of severe weather, 70% chance of lightning without severe weather. 

Cross Totals

88 89 61

33

550

468 361

86

267

65 35 3

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (≤ 19) Med (20 to 21) High (22 to 23) Very High (≥ 24)

Threat

O

ccurre

nce

Severe Lightning Non-Lightning

905 622 457 122

Figure 19. Stacked column graph of CT value thresholds. The numbers of severe days are in red, lightning days

without severe weather in green, and non-lightning days in blue. The threat criteria are based on a modified

version of the NWS SRH online glossary (NWS SRH 2005) and are on the x-axis. The cumulative frequency of 

occurrence of each type of day is shown on the y-axis. The bold numbers at the top of each column indicate the

total number of days in that threat range and the numbers within each colored portion of a column indicate the 

number of days of that type. 

3.1.9 CAPE 

The CAPE thresholds were derived from the Jacksonville NWS Severe Weather Checklist which specifies that

the threat is low when CAPE < 500 (units in J/kg), moderate when CAPE is between 501 and 1000, high when

CAPE is between 1001 and 2500, very high when CAPE is between 2501 and 3500, and extreme when CAPE >

3500. There were no CAPE values above 3000 in the stability indices database for this task so the extreme threat

category was not used. Referring to Figure 20, there were 75 days out of 588 with severe weather when the threat

20
was low, 69 days out of 562 with severe weather when the threat was medium, 107 days out of 684 with severe

weather when the threat was high and 5 days out of 26 with severe weather when the threat was very high. When

there was a low threat, lightning without severe weather occurred on 68% and severe weather on 13% of the days. 

Therefore, 20% of the days were non-lightning days. When the severe weather threat was medium, severe weather 

days accounted for 12% and lightning days without severe weather for 75% of the total. When the severe weather 

threat was high, severe weather days accounted for 16% and lightning days without severe weather for 80% of the

total. The CAPE values were in the very high threat range on only 1% of warm season days. When the CAPE values

were in the very high range, severe days occurred 19% and lightning days without severe weather 81% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 13% chance of severe weather, 68% chance of lightning without severe weather,

• Medium threat: 12% chance of severe weather, 75% chance of lightning without severe weather, 

• High threat: 16% chance of severe weather, 80% chance of lightning without severe weather, and 

• Very high threat: 19% chance of severe weather, 81% chance of lightning without severe weather. 

CAPE

75 69 107 5

398 423

545 21

115 70 32 0

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (< 0.5K) Med (0.5K to 1K) High (> 1K to 2.5K) Very High (> 2.5K)

Threat

O

ccurren

c

e

Severe Lightning Non-Lightning

588 562 684 26

Figure 20. Stacked column graph of CAPE value thresholds. The numbers of severe days are in red, lightning

days without severe weather in green, and non-lightning days in blue. The Jacksonville NWS threat criteria are on

the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold numbers 

at the top of each column indicate the total number of days in that threat range and the numbers within each colored 

portion of a column indicate the number of days of that type. 

3.1.10 CAPE Max θe

The CAPE Max θe thresholds were derived from the Jacksonville NWS Severe Weather Checklist for CAPE, 

which are defined in Section 3.1.9. Referring to Figure 21, there were 11 days out of 108 with severe weather when

the threat was low, 22 days out of 256 with severe weather when the threat was medium, 131 days out of 918 with

severe weather when the threat was high, 68 days out of 476 with severe weather when the threat was very high and 

32 days out of 186 with severe weather when the threat was extreme. When there was a low threat, lightning without

severe weather occurred on 54% and severe weather on 10% of the days. The CAPE Max θe values were in the 

21
extreme range on 10% of warm season days. When the severe weather threat was medium, severe weather days

accounted for 9% and lightning days without severe weather for 65% of the total. When the severe weather threat 

was high, severe weather days accounted for 15% and lightning days without severe weather for 74% of the total. 

When the severe weather threat was very high, severe weather days accounted for 14% and lightning days without

severe weather for 76% of the total. When the CAPE Max θe values were in the extreme range, severe days occurred 

17% and lightning days without severe weather 78% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 10% chance of severe weather, 54% chance of lightning without severe weather,

• Medium threat: 9% chance of severe weather, 65% chance of lightning without severe weather, 

• High threat: 15% chance of severe weather, 74% chance of lightning without severe weather,

• Very high threat: 14% chance of severe weather, 76% chance of lightning without severe weather, and 

• Extreme threat: 17% chance of severe weather, 78% chance of lightning without severe weather. 

CAPE Max θe

11 22 131 68 32

58 167

668 361 145

39

67

119 47 9

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (< 0.5K) M ed (0.5K to 1K) High (> 1K to 2.5K) Very High (2.6K to 3.5K) Extreme (> 3.5K)

Threat

Occurre

n

c

e

Severe Lightning Non-Lightning

108 256 918 476 186

Figure 21. Stacked column graph of CAPE Max θe value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The Jacksonville NWS threat 

criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The 

bold numbers at the top of each column indicate the total number of days in that threat range and the numbers 

within each colored portion of a column indicate the number of days of that type. 

3.1.11 CAPE FMaxT

The CAPE FMaxΤ thresholds were derived from the Jacksonville NWS Severe Weather Checklist for CAPE, 

which are defined in Section 3.1.9. Referring to Figure 22, there were 18 days out of 252 with severe weather when

the threat was low, 462 days out of 379 with severe weather when the threat was medium, 169 days out of 1172 with

severe weather when the threat was high, 26 days out of 162 with severe weather when the threat was very high and 

6 days out of 9 with severe weather when the threat was extreme. When there was a low threat, lightning without 

severe weather occurred on 54% and severe weather on 7% of the days. When the severe weather threat was

medium, severe weather days accounted for 12% and lightning days without severe weather for 69% of the total. 

22
When the severe weather threat was high, severe weather days accounted for 14% and lightning days without severe 

weather for 76% of the total. When the severe weather threat was very high, severe weather days accounted for 16% 

and lightning days without severe weather for 81% of the total. The CAPE FMaxΤ values were in the extreme range

on only 0.5% of warm season days. When the CAPE FMaxΤ values were extreme, severe days occurred 67% and

lightning days without severe weather 33% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 7% chance of severe weather, 54% chance of lightning without severe weather,

• Medium threat: 12% chance of severe weather, 69% chance of lightning without severe weather, 

• High threat: 14% chance of severe weather, 76% chance of lightning without severe weather,

• Very high threat: 16% chance of severe weather, 81% chance of lightning without severe weather, and 

• Extreme threat: 67% chance of severe weather, 33% chance of lightning without severe weather. 

CAPE FMaxT 

18 46 169 26

136 6

263

894 131

3 98

70

109 5 0

0%

20%

40%

60%

80%

100%

Low (< 0.5K) M ed (0.5K to 1K) High (> 1K to 2.5K) Very High (> 2.5K) Extreme (> 3.5K)

Threat

Occurre

n

c

e

Severe Lightning Non-Lightning

252 379 1172 162 9

Figure 22. Stacked column graph of CAPE FMaxT value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The Jacksonville NWS threat 

criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The 

bold numbers at the top of each column indicate the total number of days in that threat range and the numbers 

within each colored portion of a column indicate the number of days of that type. 

3.1.12 500 mb Temperature 

The T500 thresholds were derived from the 45 WS based on forecaster experience. The forecasters stated that, as 

a rule-of-thumb, there is a low threat of severe weather when T500 > -10 ̊C and a high threat when T500 ≤ -10 ̊C. 

Referring to Figure 23, there were 245 days out of 1890 with severe weather when the threat was low and 26 days

out of 232 with severe weather when the threat was high. The T500 values were in the low range 89% of the days 

during the warm season. When there was a low threat, lightning without severe weather occurred on 72% and severe 

weather on 13% of the days. Therefore, 15% of the days were non-lightning days. The T500 values were in the high

threat range on only 11% of warm season days. When T500 values were in the high threat range, severe days

23
occurred 11% and lightning days without severe weather 47% of the time. Therefore, 42% of the days were nonlightning days when T500 ≤ -10 ̊. 

This climatological data suggests the following implications based on the severe weather threat: 

• Low threat: 13% chance of severe weather, 72% chance of lightning without severe weather, and 

• High threat: 11% chance of severe weather, 47% chance of lightning without severe weather.

500 mb Temperature

245 26

1370

109

275

97

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Low (> -10C) High (≤ -10C)

Threat

O

c

c

urre

n

c

e

Severe Lightning Non-Lightning

1890 232

Figure 23. Stacked column graph of T500 value thresholds. The numbers of severe days are in red, lightning days

without severe weather in green, and non-lightning days in blue. The 45 WS threat criteria are on the x-axis. The

cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold numbers at the top of

each column indicate the total number of days in that threat range and the numbers within each colored portion of 

a column indicate the number of days of that type. 

3.1.13 Helicity

Helicity thresholds were derived from the NWS Melbourne, Florida description of ADAS Graphics (NWS

Melbourne 2003). If the wind veers with height helicity will be positive, if the wind backs with height helicity will

be negative. In the northern hemisphere, tornadoes associated with negative helicity are rare but they do occur, so 

negative helicity is included in this section. Helicity values are conditional – i.e. high values can occur without the 

necessary conditions to produce deep convection. Therefore, if helicity values are high, favorable atmospheric

instability and lift must also be present in order to produce a threat for rotating storms. The NWS states that this 

condition is more common along or ahead of winter or spring cold fronts, or within tropical cyclone outer rainbands. 

This condition is uncommon during the warm season that is typified by prevailing weak winds and little vertical 

shear. The exception is the local vertical shear created by the sea breeze front, outflow boundaries and the 

interaction of boundaries. These highly localized conditions are not evident in the soundings because the sea breeze 

front and other boundaries are not normally in the vicinity of the CCAFS rawinsonde during the morning sounding

times. 

The NWS definitions state that helicity values from 150 - 299 m2

/s2 imply the possible formation of weak

tornadoes of F0 - F1 on the Fujita Scale, values from 300 - 499 m2

/s2 imply the possible formation of strong 

tornadoes (F2 - F3) and values > 450 m2

/s2 imply the possible formation of violent tornadoes (F4 - F5). There were

24
no observed helicity values greater than +260 m2

/s2 or less than -120 m2/s2 in the database and there were only 27

reported tornadoes. In addition to forecasting tornado intensity, helicity is also an indicator of mid-level rotation 

which can lead to non-tornadic severe wind events. Therefore, helicity is presented as a parameter for evaluating the

possibility of a severe wind event, not just tornado formation and intensity. For the 207 severe weather events 

associated with positive helicity, there were 21 tornadoes (10%) with an average helicity of 33 m2/s2 and a range of

0 to 170 m2

/s2. For the 112 severe weather events with negative helicity, there were 6 tornadoes (5%) with an

average helicity of -22 m2

/s2 and a range of -10 to -50 m2/s2. 

Referring to Figure 24, there were 207 days out of 1380 with severe weather when the positive helicity values 

indicated the tornado threat was below the criteria for possible formation of weak tornadoes and 2 days out of 21

with severe weather when the positive helicity values indicated the possible formation of weak tornadoes. The 

helicity values were below the criteria for possible formation of weak tornadoes 99% of the days during the warm

season. When the threat of possible formation of weak tornadoes was below the weak criteria, lightning without

severe weather occurred on 72% and severe weather on 15% of the days. When the threat was for possible formation 

of weak tornadoes, severe days occurred 9% and lightning days without severe weather 48% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Below weak tornado threat: 15% chance of severe weather, 72% chance of lightning without severe

weather, and 

• Weak tornado threat: 9% chance of severe weather, 48% chance of lightning without severe weather. 

Positive Helicity

207 2

992

10

181

9

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

None (0 to 149) Weak (150 to 299)

Threat

Oc

c

urre

n

c

e

Severe Lightning Non-Lightning

1380 21

Figure 24. Stacked column graph of positive helicity value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The Melbourne NWS threat

criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The 

bold numbers at the top of each column indicate the total number of days in that threat range and the numbers 

within each colored portion of a column indicate the number of days of that type. 

Referring to Figure 25 for negative helicity values, there were 112 days out of 978 with severe weather when

negative helicity indicated the tornado threat was below the criteria for possible formation of weak tornadoes and 2 

days out of 2 with severe weather when negative helicity indicated the tornado threat was weak. The helicity values 

were below the criteria for possible formation of weak tornadoes on almost 100% of the days during the warm

25
season. When the threat of possible formation of weak tornadoes was below the weak criteria, lightning without

severe weather occurred on 70% and severe weather on 11% of the days. When threat was for the formation of weak

tornadoes, severe days occurred 0.2% and lightning days 0% of the time. 

This climatological data suggests the following implications based on the severe weather threat: 

• Below weak tornado threat t: 11% chance of severe weather, 70% chance of lightning without severe

weather, and 

• Weak tornado threat: 0% chance of severe weather, 0% chance of lightning without severe weather. 

Negative Helicity

112

0

688

178

2

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

None (0 to -149) Weak (-150 to -299)

Threat

O

c

c

urre

n

c

e

Severe Lightning Non-Lightning

978 2

Figure 25. Stacked column graph of negative helicity value thresholds. The numbers of severe days are in red,

lightning days without severe weather in green, and non-lightning days in blue. The Melbourne NWS threat

criteria are on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The 

bold numbers at the top of each column indicate the total number of days in that threat range and the numbers 

within each colored portion of a column indicate the number of days of that type. 

3.1.14 Summary of Stability Parameters 

Of the 14 stability parameters analyzed, only TT, LI, TI, SSI, CT, CAPE FMaxT and showed the possibility of

providing guidance in forecasting the occurrence of severe weather. Also, KI and PW showed the possibility of

providing guidance in forecasting the occurrence of non-severe and non-lightning weather days. These 8 are the only 

stability parameters included in the Severe Weather Decision Aid, shown in Section 3.3. In general, the severe 

weather threat was less than 18% for TT, LI, TI, SSI, and CT when their values were in the low-medium threat 

ranges. But when the values were in the high, very high, or extreme threat ranges the chance of severe weather was

generally 25% or higher. However, the occurrence of values in the high, very high, or extreme threat ranges was rare

for each parameter. Table 3 provides a summary of the severe weather threat analyses for each of the stability 

parameters that are used in the Severe Weather Decision Aid and a brief discussion of each follows. 

The TT was a significant factor only when there was a high threat when TT > 48. The high threat occurred 8%

of the time and when it did, severe weather occurred 28% of the time. It is also interesting to note that TT was in the 

low threat range (TT ≤ 45) on 64% of all warm season days.

26
The LI was a significant factor when there was a high threat when TI < -5. The high threat only occurred 3% of

the time but when it did, severe weather occurred 25% of the time. It is also interesting to note that LI was in the low 

threat range (LI ≥ -2) on 57% of all warm season days. 

The TI was a significant factor when there was a very high threat when TI > 40. The very high threat occurred 

6% of the time and when it did, severe weather occurred 21% of the time. It is also interesting to note that when TI

was in the low threat range (TI < 25) there was a 46% occurrence of non-lightning days. 

The SSI was a significant factor when there was a high threat when SSI < -2. The high threat only occurred 2%

of the time but when it did, severe weather occurred 32% of the time. It is also interesting to note that when SSI was 

in the low threat range (LI ≥ 3) there was a 35% occurrence of non-lightning days. 

The CT was a significant factor when only there was a very high threat when CT ≥ 24. The very high threat 

occurred 6% of the time and when it did, severe weather occurred 27% of the time. 

The CAPE FMaxT severe chance was almost uniformly spread among the threat categories except for the

extreme threat when CAPE FMaxT > 3500 which only occurred 0.04% of the time. When CAPE FMaxT was in the

extreme threat category, severe weather occurred 67% of the time. 

The KI was not a good predictor of severe weather but is included here because it was a good predictor of nonsevere and non-lightning days. When KI was in the low threat category (KI < 26) on 36% of the warm season days,

there was a 39% occurrence of non-lightning days. 

The PW is similar to KI in that it was not a good predictor of severe weather occurrence, but during the rare 4%

of the time PW was in the low threat category severe weather only occurred 3% of the time and 77% of the days

were non-lightning days. 

Table 3. Summary of the 8 stability parameters that showed some potential to indicate the severe weather chance. 

The most significant threat category and combined occurrence/severe occurrence are shaded in light yellow. 

Stability Parameter Low Threat Medium Threat High Threat Very High Threat Extreme Threat 

Total Totals 

Threat Level Frequency 64% 28% 8%

Severe Weather Frequency 9% 18% 29%

Lifted Index

Threat Level Frequency 57% 40% 3%

Severe Weather Frequency 10% 16% 25%

Thompson Index

Threat Level Frequency 31% 37% 26% 6% 

Severe Weather Frequency 6% 16% 16% 21% 

SSI

Threat Level Frequency 40% 58% 2%

Severe Weather Frequency 7% 16% 32%

Cross Totals

Threat Level Frequency 43% 30% 21% 6% 

Severe Weather Frequency 10% 14% 13% 27% 

CAPE FMaxT

Threat Level Frequency 13% 19% 59% 8% .04%

Severe Weather Frequency 7% 12% 14% 16% 67%

K-Index

Threat Level Frequency 36% 10% 54%

Severe Weather Frequency 8% 18% 16%

Precip. Water

Threat Level Frequency 4% 28% 68%

Severe Weather Frequency 3% 9% 15%

27
Table 4 provides a summary of the severe weather threat analyses for each of the stability parameters that did

not show potential to indicate the severe weather chance and a brief discussion of each follows. 

The SWEAT was not a good predictor of severe weather because the low threat had a higher occurrence of 

severe weather than the medium threat. The SWEAT was in the medium threat range 68% of the warm season days 

but severe weather only occurred 6% of the time while severe weather occurred 26% of the time when the threat was

in the low range. 

The CAPE was not a good predictor because the threat occurrence was almost uniformly spread among the 

threat categories except for the very high threat which occurred 1% of the time. Severe weather occurred only

slightly more frequently as the threat increased but there was only a 6% spread between the low threat and very high

threat. Additionally, the severe occurrence with a low threat was slightly higher than with a medium threat. 

The CAPE Maxθe was not a good predictor because the severe occurrence was somewhat uniformly spread

among the threat categories and the severe occurrence did not consistently increase as the threat category increased. 

The T500 was not a good predictor because severe occurrence was almost equal for temperatures above and 

below -10°C.

The helicity (+) and helicity (-) are not good predictors because the occurrence of severe weather was higher for

a lower threat for both parameters. Also helicity was in the low threat category over 99% of the time during the

warm season. 

Table 4. Summary of the 6 stability parameters that did not show potential to indicate the severe weather chance. 

Stability Parameter Low Threat Medium Threat High Threat Very High Threat Extreme Threat 

SWEAT

Threat Level Frequency 30% 68% 2% 

Severe Weather Frequency 26% 6% 47% 

CAPE

Threat Level Frequency 32% 30% 37% 1% 

Severe Weather Frequency 13% 12% 16% 19% 

CAPE Maxθe

Threat Level Frequency 6% 13% 47% 24% 10%

Severe Weather Frequency 10% 9% 15% 14% 17%

T500 > -10°C ≤ -10°C 

Threat Level Frequency 89% 11% 

Severe Weather Frequency 13% 11% 

Helicity (+)

Threat Level Frequency 99% 1% 

Severe Weather Frequency 15% 9% 

Helicity (-)

Threat Level Frequency 99.8% 0.2% 

Severe Weather Frequency 11% 0% 

3.2 Synoptic Weather Patterns

As part of an AMU study by Lambert et. al. (2005) to create an objective lightning forecast tool, lightning 

occurrence climatologies in the KSC/CCAFS vicinity for 7 flow regimes were developed based on work by Lericos

et. al. (2000). These climatologies yielded improvements in the forecast when using individual flow regimes 

probabilities over the seasonal climatological probability and 1-day persistence. This showed that the larger scale 

synoptic patterns should be considered as possible predictors of severe weather. In this study, the prevailing surface 

and upper level synoptic patterns were analyzed to determine if they could provide guidance to differentiate among

severe, lightning and non-lightning days. 

The synoptic weather patterns identified for each day were assigned to the upper-level jet streak positions and 

high pressure ridge as defined in Section 2.4. The pie charts in Figure 24 show the percent occurrence of the 

28
synoptic patterns on the severe days. On days with severe weather, the prevailing upper level features indicated there 

was no upper level jet streak 54% of the time and divergence 34% of the time. The prevailing surface ridge position 

was south of KSC/CCAFS 60% of the time. 

Severe Weather - Upper Air Jet Streak

None

54%

Ovhd

4%

Ent/Exit

8%

Div

34%

a 

Severe Weather - Surface Ridge

North

10%

None

30%

South

60%

b 

Figure 26. Pie charts showing the relationship between severe days and (a) the upper level jet streak position

and (b) surface ridge position. 

3.2.1 250 mb Jet Position 

As stated in Section 2.4, historical upper air charts similar to the example in Figure 10 were evaluated for each 

day in the 15-year period. There were no cases when the jet streak position could not be determined. Referring to

Figure 27 for the 250 mb jet streak position, there were 147 days out of 1360 with severe weather when there was no 

jet streak present, 10 days out of 132 with severe weather when the jet streak was overhead, 23 days out of 119 with

severe weather when a jet streak exit region was overhead and 91 days out of 494 with severe weather when upper

level divergence was present. There was no jet streak present 65% of the days during the warm season. When there

was no jet streak present, lightning without severe weather occurred on 72% and severe weather on 11% of the days.

When a jet streak was overhead, severe days occurred 8% and lightning without severe weather days 67% of the 

time. When a jet streak exit region was overhead, severe days occurred 19% and lightning without severe weather

days 66% of the time. When upper level divergence was present, severe days occurred 18% and lightning without

severe weather days 64% of the time. 

This climatological data suggests the following implications for the forecaster: 

• No jet streak present: 11% chance of severe weather, 72% chance of lightning without severe weather, 

• Jet streak overhead: 8% chance of severe weather, 67% chance of lightning without severe weather,

• Jet streak exit region overhead: 19% chance of severe weather, 66% chance of lightning without severe 

weather, and 

• Upper level divergence present: 18% chance of severe weather, 64% chance of lightning without

severe weather.

29
250 mb Jet Streak Position

147 10

23 91

983

88

79 314

230

34

17 89

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

None Ovhd Exit Div

Jet Position

O

c

c

urrence

Severe Lightning Non-Lightning

1360 132 119 494

Figure 27. Stacked column graph of 250 mb jet streak position categories. The numbers of severe days are in

red, lightning without severe weather days in green, and non-lightning days in blue. The position of the jet streak

is on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold 

numbers at the top of each column indicate the total number of days in that threat range and the numbers within

each colored portion of a column indicate the number of days of that type. 

3.2.2 Surface High Pressure Ridge Position 

As stated in Section 2.4, surface maps similar to that shown in Figure 11 were evaluated for each day in the 15

year period. Referring to Figure 28 for the surface high pressure ridge position, there were 28 days out of 594 with

severe weather when the surface ridge was north of KSC/CCAFS, 80 days out of 781 with severe weather when

there was no ridge present and 163 days out of 731 with severe weather when the surface ridge was south of 

KSC/CCAFS. When the surface ridge was north of the area, lightning without severe weather occurred on 73% and 

severe weather on 5% of the days. Therefore, 22% of the days were non-lightning days. When there was no ridge

present, severe days occurred 10% and lightning without severe weather days 69% of the time. When the ridge was 

south of the area, severe days occurred 22% and lightning without severe weather days 67% of the time. 

This climatological data suggests the following implications for the forecaster: 

• Surface ridge north of KSC/CCAFS: 5% chance of severe weather, 73% chance of lightning without 

severe weather,

• No surface ridge present: 10% chance of severe weather, 69% chance of lightning without severe 

weather, and 

• Surface ridge south of KSC/CCAFS: 22% chance of severe weather, 67% chance of lightning without 

severe weather.

30
 Surface High Pressure Ridge Position

28 80

163

435 540

490

131 161

78

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

North None South

Ridge Position

O

ccurre

nce

Severe Lightning Non-Lightning

594 781 731

Figure 28. Stacked column graph of surface high pressure ridge position. The numbers of severe days are in red, 

lightning without severe weather days in green, and non-lightning days in blue. The position of the surface ridge is

on the x-axis. The cumulative frequency of occurrence of each type of day is shown on the y-axis. The bold

numbers at the top of each column indicate the total number of days in that threat range and the numbers within

each colored portion of a column indicate the number of days of that type. 

3.3 Development of a Severe Weather Decision Aid 

This section describes the methodology used in developing a Severe Weather Decision Aid worksheet. The tool

was developed from the results of the technical interchange meetings held with the NWS offices and members of the

45 WS. Further discussions were held with the 45 WS Launch Weather Officers (LWO) and forecasters to 

determine appropriate values for the forecasters to assign to the questions and atmospheric stability parameters when 

completing the worksheet. 

Figure 29 shows the proposed Severe Weather Decision Aid worksheet graphical user interface (GUI). The

worksheet is a JavaScript-based tool that the forecaster can access from any computer with a Java-enabled web 

browser. The forecaster will check the appropriate box for each question or parameter. Each question or parameter 

has a value based on discussions with experienced forecasters and/or the occurrence of severe weather related to the

stability parameters. The values assigned to the stability parameters are more objective than those values assigned to

the other questions because they are based on the climatology of severe weather events. The other questions are

more subjective but are based on discussion with forecasters who have many years of experience forecasting in eastcentral Florida. An unchecked item or an answer of “Not Sure” will retain the default value of zero. The values 

range from a low of -2 to a high of +3. The question or stability parameter received a higher value if there was a 

higher occurrence of severe weather. The worksheet will automatically algebraically add the values based on the 

responses and provide a Total Threat Score. The higher the Total Threat Score, the more likely severe weather will 

occur. As of the writing of this report, it is not known what the occurrence of severe weather was related to

particular Total Threat Scores. The values and Total Threat Score can be refined over time as the worksheet is used 

by the forecasters. Each question or parameter has a help link that will give the forecaster more information about

the question and brief rationale for the value assigned to a particular question or parameter. 

The first two questions provide the forecaster with the big picture beyond the local area. The guidance

generated by the 28th Operational Weather Squadron at Shaw Air Force Base, SC and at the Melbourne, FL NWS 

31
office is focused on a much larger area than KSC/CCAFS, which provides a good first guess for the region. The rest 

of the questions in the tool require the forecasters to think about the local causes of severe weather during the warm

season regarding persistence, squall line activity, moisture boundaries, stability parameters, jet streak dynamics, 

synoptic flow regime, and sea breeze and boundary collisions. Points are subtracted if there is an easterly steering

flow, low level inversion, non-veering winds and a low-level temperature cap. Local forecaster experience indicates

that these are typically negative in severe weather development. There are three key ingredients for thunderstorm

development; moisture, instability and lift. For a thunderstorm to become severe, a fourth ingredient, shear, is

needed to give the storm rotation. This shear may be from an upper or low level jet streak, veering of the steering

flow winds or a sea-breeze and/or boundary collision. 

The question or parameter (bold faced) and corresponding text plus assigned value from the help links in the

GUI are shown below:

1. 28 OWS Southeast CONUS Hazard Discussion: Access the 28 OWS discussion at 

https://28ows.shaw.af.mil for a high-level overview of the southeastern US weather situation.

Is there a mention of a severe weather threat? The 28 OWS has forecast, watch, and warning 

responsibility for the entire southeast US. This discussion should be used as a guide for your severe weather 

forecast. Yes = 3, No = -1. 

Was there a severe weather threat mentioned in the previous discussion? Mention of severe weather in

the previous discussion that indicates a persistent pattern. Yes = 1, No = -1. 

2. KMLB Area Forecast Discussion (FXUS62): Access the NWS discussion at 

http://www.srh.noaa.gov/mlb/forecast.html. The Melbourne NWS Forecast Office forecasters have many 

years of local expertise. This discussion is coordinated with multiple NWS offices prior to dissemination and 

should be used as a guide for your severe weather forecast. 

Is there a mention of a severe weather threat? The Melbourne NWS Forecast Office forecasters have

many years of local expertise. This discussion is coordinated with multiple NWS offices prior to

dissemination and should be used as a guide for your severe weather forecast. Yes = 3, No = -1.

Was there a severe weather threat mentioned in the previous discussion? Mention of severe weather in

the previous discussion indicates a persistent pattern. Yes = 1, No = -1. 

3. Persistence: 

Has severe weather occurred in east-central Florida in the last 24 hours? If severe weather has occurred

in east-central Florida within the last 24 hours, it is likely to occur again today if the air mass and triggers

are the same. Yes = 1, No = -1.

4. Front or squall line activity: 

Has severe weather occurred in northwest Florida in the last 24 hours? Look for a front or squall line 

that triggered severe weather over northwest Florida – if the feature is moving into the local area it could 

increase instability, lift and rotation. Yes = 1, No = -1.

Is there a front or squall line in northwest Florida moving ESE (morning only)? Look for a front or

squall line that triggered severe weather over northwest Florida – if the feature is moving into the local area

it could increase instability, lift and rotation. Yes = 2, No = -1. 

5. Water vapor satellite image: 

Is there a distinct moisture/dry boundary across central Florida? Look for a dry zone boundaries in the 

water vapor imagery – these include axes of jet streams, thermal and upper-level ridges, and upper-level

anticyclones. Yes = 1, No = -1.

6. Sounding/stability parameters: 

MDPI: MDPI values over 1.0 indicate a strong microburst potential with additional energy in the downdraft. 

MDPI > 1 = 2, MDPI ≤ 1 = -1. 

K-Index: Climatology shows that when K-Index was in the moderate to high threat categories, 26 to 28 and

greater than 28, the occurrence of severe weather was 18% and 16%, respectively. But when KI < 26, 39%

32
of all days were non-lightning while severe weather occurred only 8% of the time. KI > 28 = 0, 26 to 28 = 0,

KI < 26 = -2. 

Total Totals: Climatology shows that when Total Totals was over 48, severe weather occurred 29% of the

time. Values over 48 only occurred 8% of the time. With TT values between 46 and 48, severe weather 

occurred 18% of the time and when TT values less than or equal to 45, severe weather occurred 9% of the

time. Also, when TT was less that or equal to 45, 24% of all days were non-lightning days. TT > 48 = 2, 46 

to 48 = 0, TT ≤ 45 = -1. 

Cross Totals: Climatology shows that when Cross Totals were in the very high threat category, greater than

or equal to 24, there was a 27% occurrence of severe weather. However, CT equal to or greater than 24 only

occurred on 6% of the warm season days. When CT was less than or equal to 23, the occurrence of severe

weather was nearly uniform at 10-14% among the low, moderate, and high threat categories. CT ≥ 24 = 2,

22 to 23 = 0, 20 to 21 = 0, CT ≤ 19 = 0.

Lifted Index: Climatology shows that when the Lifted Index was less than -5, there was a 25% occurrence

of severe weather. But LI was less than -5 on only 3% of the warm season days. When LI was -3 to -5,

severe weather occurrence was 16% and when LI was greater than -3, severe weather occurrence was 10%. 

LI < -5 = 3, -3 to -5 = 0, LI > -3 = 0. 

Showalter Stability Index: Climatology shows that when the Showalter Stability Index was less than -2, 

there was a 32% occurrence of severe weather. But SSI was only less than -2 on 2% of the warm season 

days. When SSI was -2 to 2, severe weather occurred 16% of the time and when SSI was greater than or 

equal to 3, severe weather occurred 7% of the time. Also, when SSI was greater than or equal to 3, nonlightning days occurred 35% of the time. SSI < -2 = 3, -2 to 2 = 0, SSI ≥ 3 = -1. 

Thompson Index: Climatology shows that when the Thompson Index was greater than 40, severe weather

occurred 21% of the time. TI greater than 40 occurred 6% of the time. When TI was between 35 and 39,

severe weather occurred 16% of the time. When TI was between 25 and 34, severe weather occurred 16% of

the time and when TI was less than 25, severe weather occurred 6% of the time. Also, when TI was less than 

25, 46% of all days were non-lightning days. TI > 40 = 2, 35 to 39 = 1, 25 to 34 = 0, TI < 25 = -1. 

Precipitable Water: Climatology shows that when Precipitable Water was equal to or greater than 1.5,

there was a 15% occurrence of severe weather. When PW was between 1 and 1.5, severe weather occurred

9% of the time and when PW was less than 1 severe weather occurred 3% of the time. PW is greater than 1.5

68% of the time so it is not a good indicator of severe weather but it is a good indicator of non-severe

weather days. PW > 1.5 = 0, 1 to 1.5 = -1, PW < 1 = -2. 

Is CAPE FMaxT > 3500 J/kg? CAPE FMaxT was not able to differentiate among severe and non-severe

days except when it was over 3500 J/kg. CAPE FMaxT was only this high 0.04% of the time but when it 

was, severe weather occurred 67% of the time. Yes = 3, No = 0. 

Are the winds veering with height from surface to 10,000 ft? A veering wind with height in the lower

part of the atmosphere is a type of directional shear often considered important for development of a rotating 

updraft. The rotating updraft of a supercell, called a mesocyclone, helps the supercell to produce extreme 

severe weather events such as large hail, strong downbursts of 80 miles per hour or more and strong to

violent tornadoes. Yes = 2, No = -1. 

Is there an inversion below 8,000 ft? This could indicate low level dry air moving in and increased

subsidence. Lack of moisture in the lower troposphere reduces the severe storm threat. Note that this 

inversion is not part of a morning surface inversion. Yes = -2, No = 1. 

Is the forecast max temp minus sounding conv temp equal to or greater than 5 °C? This difference will

indicate the lower atmosphere lift potential, turn over of the boundary layer. Warm/moist rising air will

increase the lower atmosphere instability. Yes = 1, No = -1. 

Is there an 850 mb cap (is the 850 mb temp < 20 °C)? This indicates that the lower atmosphere is to too 

warm to allow strong thermals to develop – the atmosphere is capped. The 850 MB temperature needs to be 

colder than the air at the surface for storms to develop. Yes = -2, No = 1.

33
Is the mean RH from 1000 mb to 700 mb equal to or greater than 70%? Moisture is critical for storm

development and severity. 70-90% RH is a good range, the lower atmosphere should not be too dry or moist 

for severe storm development. Yes = 1, No = -1. 

Does it look hazy outside? Normally in the warm season it is not hazy outside. Haze indicates subsidence

and trapped particulates in the low levels. Yes = -2, No = 0. 

7. Jet Dynamics: 

Upper-level speed max exit region or divergence over KSC/CCAFS? When an upper level speed max 

entrance/exit region or upper level divergence is present over KSC/CCAFS, severe weather occurs 19% of 

the time. These conditions account for 29% of all warm season days. Yes = 2, No = 0. 

Low-level jet with a south to west component from surface to 5,000 ft > 25 kts? A low level jet with a 

south to west component transports moisture and warm air advection into a developing thunderstorm

updraft. The high-speed wind and directional shear helps generate large values of helicity that can lead to

tornadogenesis or strong gusts of wind at the surface. Yes = 2, No = 0. 

8. Flow Regime Lightning Climatology: 

SW-1: Southwest flow (SW-1) over KSC/CCAFS occurs when the layer-averaged wind direction at all 3

stations is 180°-270°, indicating the Atlantic ridge is south of the Florida Peninsula. The probability of

lightning is 66%. SW-1 = 2. 

SW-2: Southwest flow (SW-2) also occurred when the ridge was between MIA and TBW, with layeraveraged wind directions of 180°-270° at JAX and TBW and 90°-180° at MIA. The probability of lightning

is 72%. SW-2 = 3.

SE-1: Southeast flow (SE-1) occurred when the ridge moved north of KSC/CCAFS with the layer-averaged

wind directions 180°-270° at JAX and 90°-180° at MIA and TBW. The probability of lightning is 51%. 

SE-1 = 1. 

SE-2: Southeast flow (SE-2) also occurred when the ridge was north of the Florida Peninsula and the layeraveraged wind direction at all three stations was 90°-180°. The probability of lightning is 39%. SE-2 = -1. 

NW: Northwest flow regime (NW) occurred when the layer-averaged wind direction at all three stations was

270°-360°. The probability of lightning is 43%. NW = 0. 

NE: Northeast flow regime (NE) occurred when the layer-averaged wind direction at all three stations was 

0°-90°. The probability of lightning is 18%. NE = -2. 

Other: When the layer-averaged wind directions at the three stations did not fit any of the above criteria, it 

was designated as Other. The probability of lightning is 44%. Other = 0.

9. Sea Breeze and Boundary Collisions: Boundary collisions will increase lift and rotation.

If a sea breeze forms, will it stay east of I-95? If so, this leaves a strong line of discontinuity (Temp, RH &

Helicity) in the forecast area. Yes = 1, No = -1. 

Are you forecasting a late developing sea breeze? If so, you are adding additional lower atmosphere

heating (lift), which will increase the instability. Yes = 1, No = -1. 

Are you forecasting or observing multiple boundary collisions? Multiple boundary collisions are often 

the single most important trigger for severe weather. Yes = 2, No = -1. 

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Figure 29. Proposed 45 WS Severe Weather Decision Aid worksheet GUI. Forecasters will answer each 

item by checking the appropriate boxes. The “Total Threat Score” will be automatically calculated and 

displayed at the bottom of the worksheet as the forecaster checks boxes. 

35
4. Summary 

This report presented a 15-year climatological study of severe weather events and related severe weather

atmospheric parameters. Data sources included local forecast rules, archived sounding data, CGLSS, surface and 

upper air maps, and two severe weather event databases covering east-central Florida. The local forecast rules were 

used to set threat assessment thresholds for stability parameters that were derived from the sounding data. The 

severe weather events databases were used to identify days with reported severe weather and the CGLSS data was

used to differentiate between lightning and non-lightning days. These data sets provided the foundation for 

analyzing the stability parameters and synoptic patterns that were used to develop an objective tool to aid in

forecasting severe weather events. The period of record for the analysis was May – September, 1989 – 2003. 

The two severe weather event databases were compared and combined to form one severe weather events

database. The days in the period were stratified into severe/non-severe event days by east-central Florida county and 

type of severe event. The CCAFS rawinsonde data were used to calculate stability indices to determine if they could 

be used to discern between the severe/non-severe days. The results showed that severe/non-severe event days were

indistinguishable based on stability index values. Therefore, the data were re-stratified into severe, lightning with no 

severe weather, and non-lightning days in an attempt to better discern among them using the stability indices. This 

re-stratification required evaluating the CGLSS data to distinguish between lightning and non-lightning days. The 

CGLSS data were displayed on a map of east-central Florida to determine which counties had lightning strikes on

each individual day. The lightning strike maps were saved as image files and then incorporated into a web-based 

lightning strike climatology tool that was delivered to the 45 WS. 

The stability indices were then used to evaluate the data with the new stratification. The results were presented

in stacked column graphs that depicted the percent occurrence of each type of day with respect to a severe weather 

threat index for each stability parameter. By displaying the data in this format, it was evident some stability

parameters provided objective guidance for the frequency of occurrence of severe weather and others provided no

guidance. This analysis also indicated that some of the stability parameters were better predictors of nonlightning/non-severe days based on certain threat values which will provide key objective information to the duty

forecaster. The upper level and surface synoptic-scale dynamics were also investigated for each day of the 15-year 

period. While jet streak interaction appears to have some influence on convective development, the location of the

surface high pressure ridge and prevailing surface synoptic flow was a clear discriminator among the three types of 

days evaluated.

Based on the results of the analyses, an interactive web-based Severe Weather Decision Aid was developed to

assist the duty forecaster by providing a level of objective guidance based on the analysis of the stability parameters,

CGLSS data, and synoptic-scale dynamics. This tool improves upon the original 45 WS Severe Weather Checklist 

(Appendix A) because it is based on a statistical climatology of 15 year’s worth of data tuned to east-central Florida,

it is more objective and it is presented in a user-friendly interactive web-based GUI. The tool will be tested and

evaluated during the 2005 warm season. 

36
References

88th Weather Squadron, 2004: Guide to Thunderstorm Stability Indices. Wright-Patterson Air Force Base, OH. 

[Available online at http://weather.wpafb.af.mil/main/forecast-tools/indices.html] 

Computer Sciences Raytheon, 2000: 45th Space Wing Eastern Range Instrumentation Handbook, Computer

Sciences Raytheon Inc., 758 pp. 

Doswell, C. A., 1991: A review for forecasters on the applications of hodographs to forecasting severe 

thunderstorms. Nat. Wea. Dig., 16 (No. 1), 2-16. 

Hart, J. A., and P. R. Janish, 2003: SeverePlot: Historical Severe Weather Report Database. Version 2.5. Storm

Prediction Center, Norman, OK. [Available online at http://www.spc.noaa.gov/software/svrplot2/] 

Insightful Corporation, 2000: S-PLUS® 6 User’s Guide, Insightful Corp., Seattle, WA, 470 pp. 

Lambert, W., M. Wheeler and W. Roeder, 2005: Objective lightning forecasting at Kennedy space center and Cape 

Canaveral air force station using cloud-to-ground lightning surveillance system data, Conference on 

Meteorological Applications of Lightning Data, 9-13 Jan 05, San Diego, CA, 9 pp. 

Lericos, T. P., H. E. Fuelberg, A. I. Watson, and R. L. Holle, 2002: Warm season lightning distributions over the 

Florida Peninsula as related to synoptic patterns. Wea. Forecasting, 17, 83 – 98. 

National Climatic Data Center, 2004: U.S. Storm Events Database. [Available online at 

http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms] 

National Climatic Data Center, 2004: Storm Data FAQ Page. [Available online at 

http://www.ncdc.noaa.gov/oa/climate/sd/sdfaq.html] 

National Weather Service Forecast Office Melbourne, 2003: Descriptions of ADAS Graphics, 0-3 km Helicity 

[Available online at http://www.srh.noaa.gov/mlb/ldis/adas_gif_definitions.html] 

National Weather Service Southern Region Headquarters, 2005: Jetstream, an online weather school [Available 

online at http://www.srh.weather.gov/jetstream/] 

Ward, J., 2004: The effect of population density on central Florida’s reported severe weather occurrences. [Available 

from the Kennedy Space Center Weather Office] 

37
List of Abbreviations and Acronyms 

Term Description 

45 WS 45th Weather Squadron 

AMU Applied Meteorology Unit

CAPE Convective Available Potential Energy

CCAFS Cape Canaveral Air Force Station 

CGLSS Cloud-to-Ground Lightning Surveillance System

CIN Convective Inhibition

CT Cross Totals 

EDT Eastern Daylight Time

GUI Graphical User Interface 

HTML HyperText Markup Language

KSC Kennedy Space Center 

KI K-Index 

LI Lifted Index 

LWO Launch Weather Officer 

MIDDS Meteorological Interactive Data Display System

NCDC National Climatic Data Center 

PW Precipitable Water 

SPC Storm Prediction Center 

SSI Showalter Stability Index

SWEAT Severe Weather ThrEAT 

T500 Temperature at 500 mb

TI Thompson Index 

TT Total Totals Index

UTC Coordinated Universal Time

38
Appendix A – 45 WS Severe Weather Worksheet 

39
Appendix B – Jacksonville, Florida NWS Severe Weather Checklist 

40
NOTICE 

Mention of a copyrighted, trademarked or proprietary product, service, or document does not constitute

endorsement thereof by the author, ENSCO Inc., the AMU, the National Aeronautics and Space Administration, or 

the United States Government. Any such mention is solely for the purpose of fully informing the reader of the 

resources used to conduct the work reported herein. 

41