NASA/TM-2013-217923

First Cloud-to-Ground Lightning Timing 

Study 

Lisa L. Huddleston 

Applied Meteorology Unit 

Kennedy Space Center, Florida 

December 2013 
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NASA/TM-2013-217923 

First Cloud-to-Ground Lightning Timing 

Study 

Lisa L. Huddleston 

Applied Meteorology Unit 

Kennedy Space Center, Florida 

National Aeronautics and 

Space Administration 

Kennedy Space Center 

Kennedy Space Center, FL 32899-0001 

December 2013 
Acknowledgements

The author would like to thank Dr. William Bauman and Ms. Winifred Crawford of the 

Applied Meteorology Unit, Dr. Francis Merceret of the Kennedy Space Center Weather Office, 

and Mr. Bill Roeder, Ms. Kathy Winters, Mr. Mike McAleenan, and Mr. Dave Craft of the 45th 

Weather Squadron for lending their time, data, and statistical expertise to this task. 

Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

This report is also available in electronic form at 

http://science.ksc.nasa.gov/amu/

 
2 

Executive Summary 

Customers: Launch Services Program (LSP) and Ground Systems Development and 

Operations (GSDO) 

NASA’s LSP, GSDO and other programs use the probability of cloud-to-ground (CG) 

lightning occurrence issued by the 45th Weather Squadron (45 WS) in their daily and weekly 

lightning probability forecasts. These organizations use this information when planning 

potentially hazardous outdoor activities, such as working with fuels, or rolling a vehicle to a 

launch pad, or whenever personnel will work outside and would be at-risk from lightning. These 

organizations would benefit greatly if the 45 WS could provide more accurate timing of the first 

CG lightning strike of the day. The Applied Meteorology Unit (AMU) has made significant 

improvements in forecasting the probability of lightning for the day, but forecasting the time of 

the first CG lightning with confidence has remained a challenge. 

To address this issue, the 45 WS requested the AMU to determine if flow regimes, wind 

speed categories, or a combination of the two could be used to forecast the timing of the first 

strike of the day in the Kennedy Space Center (KSC)/Cape Canaveral Air Force Station 

(CCAFS) lightning warning circles. The data was stratified by various sea breeze flow regimes 

and speed categories in the surface to 5,000-ft layer. The surface to 5,000-ft layer was selected 

since that is the layer the 45 WS uses to predict the behavior of sea breeze fronts, which are the 

dominant influence on the occurrence of first lightning in Florida during the warm season. Due to 

small data sample sizes after stratification, the AMU could not determine a statistical 

relationship between flow regimes or speed categories and the time of the first CG strike. . As 

expected, although the amount and timing of lightning activity varies by time of day based on 

the flow regimes and speed categories, there are extended tails of low lightning activity making 

it difficult to specify times when the threat of the first lightning flash can be avoided. However, 

the AMU developed a graphical user interface with input from the 45 WS that allows forecasters 

to visualize the climatological frequencies of the timing of the first lightning strike. This tool 

should contribute directly to the 45 WS goal of improving lightning timing capability for its NASA, 

US Air Force and commercial customers. 
3 

Table of Contents

Executive Summary................................................................................................................. 2

List of Figures.......................................................................................................................... 4

List of Tables........................................................................................................................... 5

1. Introduction ....................................................................................................................... 6

2. Data.................................................................................................................................. 7

2.1 CGLSS....................................................................................................................... 7

2.2 1000 UTC XMR Soundings ......................................................................................... 8

3. Stratification ...................................................................................................................... 9

4. Data Analysis .................................................................................................................. 11

4.1 Chi square (2

) Test for Proportions .......................................................................... 11

4.2 Marascuilo Procedure ............................................................................................... 12

5. Graphical User Interface.................................................................................................. 14

5.1 Excel Workbook........................................................................................................ 14

5.2 Sea Breeze Flow Regime Stratification PivotTables................................................... 16

5.3 Speed Category Stratification PivotTables................................................................. 18

6. Summary and Conclusions .............................................................................................. 19

References............................................................................................................................ 20

List of Acronyms.................................................................................................................... 21
4 

List of Figures 

Figure 1. The 5-NM lightning warning circles on Kennedy Space Center (KSC,blue) and 

CCAFS (red) (Crawford, 2010)................................................................................ 7

Figure 2. The GUI Introduction worksheet gives a brief description of how to use the 

lightning timing tool. This worksheet is automatically displayed when opening the 

Excel file. ............................................................................................................. 15

Figure 3. An example of the GUI using Excel 2010 slicers for the FRN flow regime 

stratification. In this example, the stratifications were the month of August, days 

when lightning occurred, medium FRN speed category, all speed categories, and 

Thompson Index ≥ 34. The top chart shows the number of times lightning 

occurred during each hour and the bottom chart shows the frequency of 

occurrence as a percentage of first lightning strike occurrences in each flow 

regime. Note that after the user selects the filters from the slicer menus, the 

categories that contain no data after filtering are grayed out and moved to the 

end of each of the slicer menus. ........................................................................... 16

Figure 4. An example of the tabular count data associated with the upper graph shown in 

Figure 3................................................................................................................ 17

Figure 5. An example of the tabular percentage data associated with the lower graph 

shown in Figure 3. ................................................................................................ 17

Figure 6. An example of the GUI using slicers for the FRN speed category stratification. In 

this example, the stratifications were the month of August, days when lightning 

occurred, all flow regimes, and Thompson Index ≥ 34. The top chart shows the 

number of times lightning occurred during each hour and the bottom chart shows 

the frequency of occurrence as a percentage of first lightning strike occurrences 

in each flow regime. Note that after the user selects the filters from the slicer 

menus, the categories that contain no data after filtering are grayed out and 

moved to the end of each of the slicer menus........................................................ 18

 
5 

List of Tables 

Table 1. The eight 45 WS sea breeze flow regime sectors in the surface to 5,000-ft layer 

as defined in the 45 WS FRN.................................................................................. 9

Table 2. The alternate two- and four-sector sea breeze flow regimes for the surface to 

5,000-ft layer. ....................................................................................................... 10

Table 3. The mean surface to 5,000-ft layer four-speed stratifications and alternate threespeed stratifications. ............................................................................................. 10

Table 4. Results from the 2

 tests. H0 is the null hypothesis indicating no significant 

statistical relationship between the first strike of the day and flow regime or speed 

category stratifications. H1 is the alternate hypothesis indicating a significant 

statistical relationship between the first strike of the day and flow regime or speed 

category stratifications. ......................................................................................... 12

Table 5. TI thresholds from Vasquez (2006). ...................................................................... 14
6 

1. Introduction 

NASA’s Launch Services Program (LSP) and Ground Systems Development and 

Operations (GSDO) program along with other programs use the probability of cloud-to-ground 

(CG) lightning occurrence issued by the 45th Weather Squadron (45 WS) in their daily and 

weekly lightning probability forecasts. These forecasts are important in the warm season 

months, May-October, when the area is most affected by lightning. This study is restricted to the 

warm season because most of the lightning in Florida occurs then, and lightning activity in 

Florida in the summer is driven primarily by heating of the land by the Sun and has a strong 

repeatable diurnal behavior. As a result, it is reasonable to expect a tool to predict the timing 

can be created. The timing of lightning during the cool season is much less challenging since it 

is associated with approaching weather fronts, which can be predicted fairly well by numerical 

weather prediction models. In addition, the amount of lightning is much less in Florida during the 

cool season. LSP, GSDO and other programs use this information when planning potentially 

hazardous outdoor activities, such as working with fuels, or rolling a vehicle to a launch pad, or 

when people will be working outside and at-risk from lightning. These organizations would 

benefit greatly if the 45 WS could provide more accurate timing of the first CG lightning of the 

day in addition to the probability of lightning occurrence. The AMU has made significant 

improvements in forecasting the probability of lightning for the day (Lambert and Wheeler 2005; 

Lambert 2007; Crawford 2010; Crawford and Bauman 2012). However, forecasting the time of 

the first CG lightning is still difficult. 

For this task, the 45 WS requested the AMU to stratify the data by sea breeze flow regimes 

and speed categories in the surface to 5,000-ft layer, both defined in the 45 WS Forecast 

Reference Notebook (FRN), along with some alternate stratifications if the sample size from the 

original stratifications did not have enough samples to allow statistical comparison. The surface 

to 5,000-ft layer was selected since that is the layer the 45 WS uses to predict the behavior of 

sea breeze fronts, which are the dominant influence on the occurrence of first lightning in 

Florida during the warm season. The 45 WS also requested a graphical user interface (GUI) 

displaying the frequencies and percentages of the timing of lightning under the various 

stratifications. The AMU found no statistically significant differences among the various 

stratifications, but the 45 WS determined that a GUI would still be helpful to the forecasters and 

Launch Weather Officers (LWOs) to visualize patterns in the stratified data and provide useful 

guidance to the launch customers. 
7 

2. Data 

The data used in this task were from the 45th Space Wing CG component of the Four 

Dimensional Lightning Surveillance System (4DLSS) and the 1000 UTC Cape Canaveral Air 

Force Station (CCAFS) soundings (XMR). The CG component of 4DLSS is better known by its 

previous name, the CG Lightning Surveillance System (CGLSS), therefore, that term will be 

used hereafter in this report. The period of record (POR) is 1989-2011 or the warm-season 

months of May-October. Note that CGLSS began reporting strokes rather than flashes in April 

2008. Flash data was used in this study prior to 2008 and stroke data was used from 2008 to 

2011. The difference between using first flash and first stroke would be fractions of a second 

apart and are thus inconsequential for the scope of this study. The AMU has the processed 

XMR and CGLSS data from previous tasks and used them to create distributions of time of the 

first CG strike in the KSC/CCAFS 5 NM lightning warning circles (Figure 1). 

Figure 1. The 5-NM lightning warning circles 

on Kennedy Space Center KSC (blue) and 

CCAFS (red) (Crawford, 2010). 

2.1 CGLSS 

CGLSS is a network of six sensors that detects CG strokes on KSC/CCAFS and the 

surrounding area. It reports the date, time, latitude, longitude, peak current, polarity, and 

location error ellipse information of each detected stroke. The AMU has the processed the 

CGLSS data for previous tasks to include CG strikes that occurred in the KSC/CCAFS warning 

circles (Figure 1) for which the 45 WS has forecasting responsibility and for times between 0700 

and midnight local time and are covered in the daily planning forecast issued by 45 WS. The 

CGLSS data were further filtered using Microsoft Access to capture the hour of the first lightning 

strike of the day after 0700 local time. 
8 

2.2 1000 UTC XMR Soundings 

The AMU filtered the 1000 UTC XMR data to only include observations between the surface 

and 700 mb (~10,000 ft). According to the 45 WS FRN, the forecasters use the average 

direction in a sea breeze layer from the surface to 5,000 ft. The AMU used Microsoft Access to 

filter the data further to include only data in this sea breeze layer. The average surface to 5,000-

ft winds were then calculated and used to determine the sea breeze flow regime of the day. 
9 

3. Stratification 

The AMU and 45 WS held a meeting to discuss ways of stratifying the data into sea breeze 

flow regimes and speed categories. The 45 WS requested the AMU make an attempt to stratify 

the data by sea breeze flow regime for the surface to 5,000-ft layer and the speed regime, both 

as outlined in the 45 WS FRN. Some simplified stratification methods were also discussed in 

case there were not enough data in one or more of the stratification methods to create robust 

statistics in determining a relationship between the flow regime/speed stratifications and the 

time of the first CG strike. Table 1 shows the eight sea breeze flow regimes as defined in the 

FRN. Table 2 shows the alternated two- and four-sector sea breeze flow regimes that would be 

used if there were not enough data in the eight-sector stratifications. Table 3 shows the fourspeed stratifications, and the alternate three-speed stratifications that would be used if there 

were not enough data in the four-speed stratifications. These speed ranges are based on the 

values in the 45 WS FRN that define different speed stratifications for each sea breeze flow 

regime. 

Table 1. The eight 45 WS sea breeze flow 

regime sectors in the surface to 5,000-ft 

layer as defined in the 45 WS FRN. 

Sea Breeze 

Flow Regime Direction Sector

East (E) >66o and ≤110̊o

Southeast (SE) >110o and ≤155o

South >155o and ≤200o

Southwest (SW) >200o and ≤245o

West >245o and ≤290o

Northwest (NW) >290o and ≤335o

North >335o or ≤20o

Northeast (NE) >20o and ≤66o

(a) 
10 

Table 2. The alternate two- and four-sector sea breeze 

flow regimes for the surface to 5,000-ft layer. 

Stratification Sea Breeze 

Flow Regime Direction Sector 

Two-Sector 

Off-Shore ≥135o and <315o

On-Shore ≥315o or <135o

Four-Sector 

Off-Shore SW ≥135o and <225o

Off-Shore NW ≥225o and <315o 

On-Shore NE ≥315o or <45o

On-Shore SE ≥45o and <135o

Table 3. The mean surface to 5,000-ft layer four-speed 

stratifications and alternate three-speed stratifications. 

# Speed 

Stratifications 

Stratification 

Name Wind Speed Range 

Four 

(FRN)

Low ≤5 kt

Medium >5 kt and ≤11 kt

Medium High >11 kt and ≤16 kt

High >16 kt 

Three 

(alternate) 

Low ≤7.7 kt

Med >7.7 kt and ≤12.6 kt

High >12.6 kt 

 
11 

4. Data Analysis 

The AMU analyzed the stratified data sets described above to determine if there was a 

relationship between any of the flow regime/speed combinations and the timing of the first 

lightning strike of the day. In most cases, the analysis showed that stratification to the requested 

levels resulted in sample sizes that were too small for meaningful statistical analysis. 

Accordingly, the AMU performed analysis on data stratified by either the flow regimes in Table 1 

and Table 2 or the speed stratifications in Table 3, but not combined. 

4.1 Chi square (2

) Test 

The AMU used the chi-square (2

) statistical significance test to determine whether there 

was a significant relationship between the time of the first lightning strike of the day and any of 

the sea breeze flow regimes or speed stratifications. The 2

 test requires a null hypothesis (H0), 

which is that no significant relationship exists between the flow regimes or speed categories and 

the first lightning strike of the day. H0 can either be rejected as being improbable or not rejected. 

Note that H0 is never accepted, just not rejected. Not rejecting H0 means there is not enough 

evidence to reject the hypothesis; it does not mean that the hypothesis is valid. The alternative 

hypothesis (H1) is that there is a significant relationship between the flow regime sectors or 

speed categories and the first lightning strike of the day. 

For the first step in the 2

 test, the AMU determined the observed number of strikes in each 

hour for each stratification and, from the observed values, calculated the associated expected 

number of strikes. The expected number of strikes was calculated by multiplying the number of 

strikes in each hour by the number of strikes in a flow regime sector or speed category 

regardless of time, then dividing that number by the total number of first lightning strikes of the 

day in the POR. For example, the total number of first strikes in the eight-sector easterly (E in 

Table 3) flow regime over all hours was 64. The total number of first strikes in the 0700 local 

hour was 35. These two values were multiplied and then divided by the total number of first 

strikes of the day over all hours and flow regimes for the POR, which 1,282. The expected 

number of first strikes for the 0700 local hour in the E flow regime was (64*35)/1282 = 1.75. This 

essentially assumes the distribution of first strikes is random, which is the same as assuming 

there is no significant influence from the flow regimes or speed categories. While it is not 

possible to have a fractional number of first strikes, this expected value, 1.75, is what was 

needed for the 2

 calculation. The observed number of first strikes for this stratification was 5. 

After all expected frequencies were calculated, the 2

 statistic was calculated using the 

equation 

 

Expected

Observed Expected

#

# # 2

2     (Wilks 2006). 

The degrees of freedom of the 2

 statistic is (r-1)*(c-1), where r is the number of rows and c is 

the number of columns in the contingency table. Following from the example above, the number 

of rows is equal to 17, since the data are consolidated by hour and there are 17 hours for each 

day in the dataset (0700-2300 local time). The hour designation is the start of the hour. For 

example 0700 signifies the time between 0700 and 0800 and 2300 signifies the time between 

2300 and 0000. The number of columns for the 45 WS sea breeze flow regime sectors is 8. 

The degrees of freedom in this case is (17 – 1)*(8 – 1) = 112. 
12 

Then the AMU compared the calculated 2

 statistic to an associated 2 critical value in a 

standard 2

 distribution table using the α = 0.05 level of significance. If the calculated 2 statistic 

was greater than the 2

 critical value, then H0 was rejected with the assumption that there was a 

significant relationship between the first strike of the day and flow regime or speed category. 

Otherwise, if the statistic was less than the critical value and H0 could not be rejected, it could 

be concluded with some certainty that there was no statistically significant relationship between 

the first strike of the day and flow regime or speed category. 

Table 4 shows the overall results of the analysis. The only statistically significant outcome in 

which H0 could be rejected was for the two-sector flow regimes (Table 2). For the 2

 test to give 

accurate results, most expected values must be large. Dixon and Massey (1983) define this as 

no more than 20% of the expected values being < 5. Based on this restriction, the 2

 test was 

invalid for the eight- and four-sector flow regime stratifications. All stratifications (either flow 

regime or speed category) that divided the data into more than two groups caused the resulting 

datasets to be too small for meaningful statistical analysis such that H0 could not be rejected. 

Table 4. Results from the 2tests. H0 is the null hypothesis indicating 

no significant statistical relationship between the first strike of the day 

and flow regime or speed category stratifications. H1 is the alternate 

hypothesis indicating a significant statistical relationship between the 

first strike of the day and flow regime or speed category stratifications. 

Stratification Status Comments 

Eight-sector flow regimes 

(Table 1) 2 test invalid More than 20% of expected values < 5 

Two-sector flow regimes 

(Table 2) Reject H0

Significant relationship 

with first strike 

(p-value = 0.000) 

Four-sector flow regimes 

(Table 2) 2 test invalid More than 20% of expected values < 5 

Four-speed categories 

(Table 3) Fail to reject H0

No relationship to first 

strike found 

(p-value = 0.081) 

Three-speed categories 

(Table 3) Fail to reject H0

No relationship to first 

strike found

(p-value = 0.312) 

4.2 Marascuilo Procedure 

Even though the 2

 test showed a statistically significant relationship with the two-sector flow 

regimes, i.e. there are differences in the first lightning strike occurrence between onshore and 

offshore flow, the 2

 test does not show which time period or periods caused the difference. In 

order to test which times were different, the AMU used the Marascuilo procedure 

(NIST/SEMATECH 2013). The Marascuilo procedure performs comparisons between all pairs of 

time periods simultaneously and can identify the times likely responsible for rejecting H0. 
13 

To start the Marascuilo procedure, The AMU counted the number of hours for which data 

were available for the onshore and offshore stratifications. There were 17 hours each of 

onshore and offshore flow, equaling 34 time periods. The total number of pairs of data to 

compare was calculated using the formula r*(r-1)/2, where r is the number of groups of data, in 

this case 34. The total number of data pairs in this test was 34*33/2 = 561. This results in the 

absolute difference of the proportion of the first lightning strike occurrence between onshore and 

offshore flow at every time period being compared to the first lightning strike occurrence 

between onshore and offshore flow at every other time period. The absolute values of these 

differences are the test statistics. The next step was to pick a significance level (0.05) and 

compute the corresponding critical values for each pairwise comparison of proportions using the 

following formula. 

   

k

k k

i

i i

U

n

p p

n

p p  	   2 1 1 CriticalRange 

Where pi

 is the proportion of the first lightning strike occurrence in a particular hour and flow 

regime, pk is the proportion of the first lightning strike occurrence in a different hour and flow 

regime, ni and nk are the counts of occurrences of the first lightning strike occurrence in a 

particular hour and flow regime for the POR, and 2

U is the upper tail critical value of the chisquare distribution having r-1 (33) degrees of freedom. If the absolute difference in the data pair 

was greater than its critical range, then it could be concluded that observed values were 

significantly different from each other (Levine et al. 2007). 

Unfortunately, the Marascuilo procedure did not find any observed values that were 

significantly different from one another, mostly likely due to the small group sizes after 

stratification by hour as needed for the procedure. 
14 

5. Graphical User Interface 

Although the number of observations in each of the stratifications was too small to 

determine relationships to the first lightning strike of the day, the AMU asked the 45 WS if 

providing a GUI displaying the frequencies and percentages of the timing of lightning under the 

various stratifications would be helpful. The 45 WS agreed that such a GUI would be helpful to 

the forecasters and LWOs in generating their daily forecasts for lightning timing. The 45 WS 

LWOs also requested that a Thompson Index (TI) stratification be added to the GUI to account 

for stability and moisture. In previous AMU studies (Lambert 2005, Lambert 2007, Crawford 

2010, Bauman and Crawford 2012), TI was an important predictor of lightning occurrence for 

most of the warm season months. The TI stratification thresholds in the GUI were adapted from 

Vasquez (2006) and are shown in Table 5. The GUI displays the climatological statistics for the 

times of the first lightning strike of the day in each month, flow regime direction, wind speed 

category and TI stratification. 

Table 5. TI thresholds adapted from Vasquez 

(2006).

TI Description 

<25 No thunderstorm 

≥25 to <34 Potential of thunderstorms 

≥35 to <40 Potential of thunderstorms 

approaching severe 

≥40 Potential of severe thunderstorms 

5.1 Excel Workbook 

The GUI was developed using the slicers feature in Excel 2010. Slicers, which are new to 

Excel 2010, are embedded graphic objects that allow the user to quickly and easily filter data in 

an Excel PivotTable using multiple criteria. Slicers can also be used to filter data in more than 

one PivotTable created in the workbook simply by connecting additional tables. Slicers show 

which filtering criteria are currently selected in the connected PivotTables (Harvey 2010). The 

45 WS LWOs and forecasters provided input to the final design of the GUI to make sure it met 

their operational needs. 

The Excel workbook with the GUI contains six worksheets. The first worksheet is the 

Introduction worksheet. It is displayed automatically upon opening this Excel file and contains a 

brief description of how to use the lightning timing GUI. It also emphasizes to the user that the 

sample sizes were small so the data should be used for visualization only and not for making 

statistically based predictions. Figure 2 shows the Introduction worksheet. The next three 

worksheets contain the PivotTable slicers for the three sea breeze flow regime stratifications 

discussed in Section 3. The last two worksheets contain the PivotTable slicers for the two 

speed category stratifications also discussed in Section 3. 
15 

Figure 2. The GUI Introduction worksheet gives a brief description of how to use the lightning 

timing tool. This worksheet is automatically displayed when opening the Excel file. 
16 

5.2 Sea Breeze Flow Regime Stratifications 

Error! Reference source not found. shows an example of the GUI with slicers from 

orksheet “SeaBreezeFlow1” (tab name at bottom of Figure 3) for the FRN sea breeze flow 

regime stratification (Table 1). Note that in this example, although the selection boxes for both 

the FRN speed and alternate speed categories (Table 3) are shown, the user is expected to 

select from one or the other, but not both. This aspect of the GUI is emphasized during 

customer training. The user can clear the slicer selections by clicking on the funnel icon in the 

upper right corner of each slicer or by pressing the “Clear All Filters” button below the slicer 

menus. 

Figure 3. An example of the GUI using Excel 2010 slicers for the FRN flow regime 

stratification. In this example, the stratifications were the month of August, days when lightning 

occurred, medium FRN speed category, all speed categories, and Thompson Index ≥ 34. The 

top chart shows the number of times lightning occurred during each hour and the bottom chart 

shows the frequency of occurrence as a percentage of first lightning strike occurrences in each 

flow regime. Note that after the user selects the filters from the slicer menus, the categories that 

contain no data after filtering are grayed out and moved to the end of each of the slicer menus. 

The user can see the tabular data in the PivotTables corresponding with the graphs by 

scrolling to the right of the graphs for the counts and to the right of the graphs and down for the 

percentages. Figure 4 and Figure 5 show examples of the counts and percentages 

corresponding to the example shown in Figure 3. 
17 

Figure 4. An example of the tabular count data associated with the upper graph shown in 

Figure 3. 

Figure 5. An example of the tabular percentage data associated with the lower graph shown in 

Figure 3. 

The worksheets “SeaBreezeFlow2” and “SeaBreezeFlow3” are similar to worksheet 

“SeaBreezeFlow1” except the slicers use the two- and four-sector sea breeze flow regimes 

outlined in Table 2 rather than the FRN sea breeze flow regime sectors. The user can clear the 

slicer selections on these worksheets by clicking on the funnel icon in the upper right corner of 

each slicer or by pressing the “Clear All Filters” button below the slicer menus. 
18 

5.3 Speed Category Stratification 

Error! Reference source not found. (from worksheet “SpeedCategory1”) shows an 

xample of the GUI using slicers for the FRN speed category stratification (Table 3). Note that in 

this example, although the selection boxes for all three sea breeze flow regimes (Table 1 and 

Table 2) are shown, the user is expected to select from only one of the three sea breeze flow 

regime slicers. This aspect of the GUI is emphasized during customer training. 

Figure 6. An example of the GUI using slicers for the FRN speed category stratification. In this 

example, the stratifications were the month of August, days when lightning occurred, all flow 

regimes, and Thompson Index ≥ 34. The top chart shows the number of times lightning 

occurred during each hour and the bottom chart shows the frequency of occurrence as a 

percentage of first lightning strike occurrences in each flow regime. Note that after the user 

selects the filters from the slicer menus, the categories that contain no data after filtering are 

grayed out and moved to the end of each of the slicer menus. 

Similar to the flow regime example in Section 5.216, the user can see the tabular data, 

corresponding with the graphs by scrolling to the right of the graphs for the counts and to the 

right of the graphs and down for the percentages. The textual data is similar to that shown in 

Figure 4 and Figure 5. The worksheet “SpeedCategory2” is similar to worksheet 

“SpeedCategory1” except the slicers use the alternate three-speed category stratification 

outlined in Table 2 rather than the FRN four-speed category stratification. The user can clear 

the slicer selections on these worksheets by clicking on the funnel icon in the upper right corner 

of each slicer or by pressing the “Clear All Filters” button below the slicer menus.
19 

6. Summary and Conclusions 

NASA’s LSP, GSDO, and other programs use the probability of CG lightning occurrence 

issued daily by the 45 WS when planning potentially hazardous outdoor activities, such as 

working with fuels, or rolling a vehicle to a launch pad, or when people will be working outside 

at-risk from lightning. While the AMU has made significant improvements in forecasting the 

probability of lightning for the day, forecasting the time of the first CG lightning is still difficult. 

LSP, GSDO, and other programs would benefit greatly if the 45 WS could provide more 

accurate timing of the first CG lightning of the day in addition to the probability of lightning 

occurrence. 

To address this issue, the 45 WS requested the AMU to determine if flow regimes, wind 

speed categories, or a combination of the two could be used to forecast the timing of the first 

strike of the day. The AMU stratified the data by sea breeze flow regimes and speed categories 

in the surface to 5,000-ft layer as defined in the 45 WS FRN for sea breeze front behavior, along 

with some alternate stratifications. The 45 WS also requested a GUI displaying the frequencies 

and percentages of the timing of lightning under the various stratifications. 

The AMU used the 2

 test to determine if statistical relationships existed between the time of 

the first CG strike and flow regime and/or speed category. In most cases, the analysis showed 

that stratification to the requested levels resulted in sample sizes that were too small for 

meaningful statistical analysis. The only statistically significant outcome using the 2

 test was for 

the two-sector flow regimes, meaning there were differences in the first lightning strike 

occurrence between onshore and offshore flow regimes. The 2

 test did not show which time 

period or periods caused the difference. In order to test which times were different, the AMU 

used the Marascuilo procedure to perform comparisons between all time periods and onshore 

and offshore flow regimes simultaneously and identify the time periods and flow regimes likely 

responsible for the significant outcome. Again due to the small sample sizes, the Marascuilo 

procedure did not find any observed values that were significantly different from one another. 

Even though the sample sizes were too small for meaningful statistical analysis, the AMU 

and 45 WS agreed that providing a GUI displaying the climatological frequencies and 

percentages of the timing of lightning under the various stratifications would be helpful to the 

forecasters and LWOs in generating their daily forecasts for lightning timing. The GUI displays 

the climatological statistics for the times of the first lightning strike of the day in each 

stratification month, flow regime sector, wind speed category, and TI. The AMU delivered the 

GUI to the 45 WS and they now use it in daily warm season operations. This tool should 

contribute directly to the 45 WS goal of improving lightning timing forecasts for its NASA, US Air 

Force and commercial customers. 

It is possible more data from a longer POR would improve the statistics. However, because 

only the first lightning strike of the day is used, it will take a number of years to build the 

database, after stratifying, to the minimum number of observations required to test for statistical 

significance. In the meantime, the AMU is developing a locally tuned, high resolution mesoscale 

model for the Eastern Range. As part of that task, the AMU could look into implementing a 

lightning prediction algorithm that may lead to breakthroughs in predicting the timing of the first 

lightning strike of the day. It is also possible that a conditional climatology of lightning probability 

could be useful, e.g. given that one strike has been observed, what are the new probabilities for 

lightning at subsequent times. However, that will likely have even more problems with small 

sample size. 
20 

References 

Bauman III, William H. and W. Crawford, 2012: Objective Lightning Probability Forecasting for 

Kennedy Space Center and Cape Canaveral Air Force Station, Phase IV. NASA Contractor 

Report CR-2012-216312, Kennedy Space Center, FL, 26 pp. [Available from ENSCO, Inc., 

1980 N. Atlantic Ave., Suite 830, Cocoa Beach, FL, 32931 and online at 

http://science.ksc.nasa.gov/amu/final.html.] 

Crawford, W., 2010: Objective Lightning Probability Forecasting for Kennedy Space Center and 

Cape Canaveral Air Force Station, Phase III. NASA Contractor Report CR-2010-216292, 

Kennedy Space Center, FL, 30 pp. [Available from ENSCO, Inc., 1980 N. Atlantic Ave., 

Suite 830, Cocoa Beach, FL, 32931 and online at 

http://science.ksc.nasa.gov/amu/final.html.] 

Dixon, W. and F. Massey, Jr., 1983: Introduction to Statistical Analysis, 4th ed. McGraw-Hill, 

672 pp. 

Harvey, G., 2010: Excel 2010 Workbook for Dummies. Wylie Publishing, Inc., 396 pp. 

Lambert, W., and M. Wheeler 2005: Objective Lightning Probability Forecasting for Kennedy 

Space Center and Cape Canaveral Air Force Station. NASA Contractor Report CR-2005-

212564, Kennedy Space Center, FL, 46 pp. [Available from ENSCO, Inc., 1980 N. Atlantic 

Ave., Suite 830, Cocoa Beach, FL, 32931 and online at 

http://science.ksc.nasa.gov/amu/final.html.] 

Lambert, W., 2007: Objective Lightning Probability Forecasting for Kennedy Space Center and 

Cape Canaveral Air Force Station, Phase II. NASA Contractor Report CR-2007-214732, 

Kennedy Space Center, FL, 57 pp. [Available from ENSCO, Inc., 1980 N. Atlantic Ave., 

Suite 830, Cocoa Beach, FL, 32931 and online at 

http://science.ksc.nasa.gov/amu/final.html.] 

Levine, D., D. Stephan, T. Krehbiel, and M. Berenson, 2007: Statistics for Managers Using 

Microsoft Excel. Prentice Hall, 858 pp. 

NIST/SEMATECH e-Handbook of Statistical Methods, http://www.itl.nist.gov/div898/handbook/, 

accessed 3/2/2013. 

Vasquez, T., 2006: Weather Forecasting Red Book. Weather Graphics Technologies, 304 pp. 
21 

List of Acronyms 

4DLSS Four Dimensional Lightning 

Surveillance System 

45 WS 45th Weather Squadron 

AMU Applied Meteorology Unit 

CCAFS Cape Canaveral Air Force 

Station 

CG Cloud-to-Ground 

CGLSS CG Lightning Surveillance 

System 

E East 

FRN Forecast Reference Notebook 

GSDO Ground Systems Development 

and Operations 

GUI Graphical User Interface 

Ho Null hypothesis 

H1 Alternative hypothesis 

KSC Kennedy Space Center 

LSP Launch Services Program 

LWO Launch Weather Officer 

N North 

NE Northeast 

NM Nautical mile 

NW Northwest 

POR Period of Record 

S South 

SE Southeast 

SW Southwest 

TI Thompson Index 

W West 

XMR CCAFS rawinsonde 3-letter 

identifier 

2 Chi-squared 
22 

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fully informing the reader of the resources used to conduct the work reported herein. 
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12/31/2013 Final November 2012 - December 2013

First Cloud-to-Ground Lightning Timing Study

Lisa L. Huddleston

Kennedy Space Center Weather Office 

Mail Code: GP-B 

Kennedy Space Center, FL 32899 

NASA/TM-2013-217923

Unclassified, Unlimited

Electronic versions of all Applied Meteorology Unit final reports can be found at http://science.ksc.nasa.gov/amu/final.html

The AMU was requested to determine if flow regimes, or wind speed categories could be used to forecast the timing of the 

first strike of the day in the Kennedy Space Center/Cape Canaveral Air Force Station lightning warning circles. Due to small 

data sample sizes the AMU could not determine a statistical relationship between flow regimes or speed categories and the 

time of the first lightning strike. However, the AMU developed a graphical user interface that allows forecasters to visualize 

the climatological frequencies of the timing of the first lightning strike.

weather, meteorology, lightning, cloud-to-ground (CG) strike, first strike of the day, timing, statistical analysis, Kennedy 

Space Center, Cape Canaveral Air Force Station, Applied Meteorology Unit 

U UU UU UU 22

Lisa L. Huddleston

(321) 861-4952