# Presentation: 138727

## Forecasting Convective Mode and Severity

- Mark F. BrittNational Weather ServiceSt. Louis, MO

## Why Am I Here?

- 	A Basic Review of Severe Thunderstorm Forecasting.
- Examine moisture return,instability, and shear  calculations.
- Examine how the amount and distribution of instability, vertical shear, and forcing interact to determine cell type, convective mode (linear or discrete), and coverage.
- Determine what type(s) of severe weather to expect for a given environment.

## Using Numbers

- There are _**NO**_ “magic” numbers or thresholds.  They are merely guidelines.
- Best to look where several key parameters overlap instead of depending on one index.
- You should look at skew-Ts and hodographs (observed and forecast) to better understand what the numbers mean.
- Increase your situation awareness by using near storm environment data, but do not use it solely to make warning decisions.

## Objective Analysis

- Available on AWIPS using MSAS, LAPS, or RUC40 analysis (Thompson/Edwards (2002) found RUC analysis is a reasonable proxy to observed soundings in supercell environments.)
- Or, the SPC Mesoanalysis Page:
- 		 http://www.spc.noaa.gov/exper/mesoanalysis/
- Displays three movable regions that is usually available by 20 minutes past each hour
- Displays a robust set of hourly objective analysis datasets using the latest surface observations and upper air analysis from the RUC.  Depicted contours highlight important “thresholds”.
- Several new parameters available this year.

## Ingredients for Deep, Moist Convection

- Moisture: (Gulf of Mexico, evapotranspiration)
- Instability: (Steep lapse rates either from the Elevated Mixed Layer off the Rockies, or large scale “dry” ascent ahead of a trough.)
- Forcing: (Surface frontal boundary,  convective outflow,  900-800mb moisture convergence at nose of nocturnal low level jet, orographic lift over the eastern Ozarks)

## Moisture Return

-  Look for rapid moisture advection from the Gulf of Mexico in strong pressure gradients ahead of a strong storm system.
-   Ridging associated with surface highs in or near the Gulf can inhibit moisture return.

- Lanicci and Warner (1991)

## Assessing Instability

- 	Which is best?
- SBCAPE
- MLCAPE
- MUCAPE

## SBCAPE:  Surface Based.  Uses the surface temperature and dew point.  Will show large diurnal swings.  Can give significant overestimates (an order of magnitude) in cases of shallow moisture and underestimates in cases of elevated convection.

- From Peter Banacos, SPC (2003)

## MLCAPE:  Mean Layer.   Uses the mean temperature and mean mixing ratio in the lowest part of the atmosphere (SPC uses lowest 100 mb).  Less variable in time and space, and more conservative than MUCAPE when lower atmosphere is not well mixed.

- From Peter Banacos, SPC (2003)

## MUCAPE:  Most Unstable Parcel.  Uses most unstable parcel in lower atmosphere (SPC uses lowest 300mb).  Helps with nocturnal or other types of elevated convection.

- From Peter Banacos, SPC (2003)

## CAPE vs. Parcel Selection

- April 22nd, 2004

- From Jon Davies Webpage

- Surface Based CAPE

- Mean Layer CAPE

## Surface Based Parcels

- Violent tornado outbreak over western Missouri.
- May 4th, 2003

## Elevated Based Parcels

- Numerous Reports of Hailin Eastern NE/ Western IA
- May 4th, 2003

## How Tall is the CAPE?

- April 22nd, 2004

- From Jon Davies Webpage (http://members.cox.net/jdavies1/)

## How Tall is the CAPE?

- April 22nd, 2004

- From Jon Davies Webpage

## How Wide Is the CAPE?

- Larger differences between parcel temperature and the environmental temperature means stronger updrafts that are less susceptible to entrainment.

## Lapse Rates

- Craven (2000) found in a study of 65 major tornado outbreaks that 6.7o C/km is a useful lower limit.  He also found low shear environments that produce tornadoes have steeper lapse rates.
- Steep mid level lapse rates (850-500 mb) have more conditional instability and increased CAPE.
- Steep low level lapse rates (0-3km AGL) can give a better idea on how quickly convection will develop.

## Mid Level Lapse Rates

## Assess Vertical Shear

- Distribution of vertical shear will determine dominant thunderstorm type.
- Can be determined using either:
- Traditional fixed layers (0-6km bulk shear, 0-1km SRH)
- “Effective” shear which accounts for ***sounding dependent*** inflow layer through CAPE and CIN constraints.  (Large sample testing suggests that “effective layer” is best defined by _>_100 J kg-1 CAPE and _<_250 J kg-1 CIN. (Thompson et al, 2004a & b))
- Low level curvature can determine if right-movers, left-movers, or both kinds of splits are favored.

## Storm Type:  Ordinary Cells

- Dominant Type in Weak Shear Environments
- Pulse Type Severe Storms.

## Storm Type:  Multicells

- Moderate to strong shear is confined mainly to the lower levels (0 to 3 km AGL)

## Organized Multicells

- >40kt 0-6 km shear
- >30kt 700-500mb wind
- Dry (low theta-e) midlevel air (strong cold)
- Downshear SBCAPE max
- System relative convergence acting downshear to enhance forward propagation

## Storm Type:  Supercells

-  A storm that possesses a persistent mesocyclone that can be sustained on the order of tens of minutes.
-  90% of this type associated with some kind of severe weather (Burgess and Lemon, 1991)

## 0-6 km Shear Magnitude

- General deep layer shear “thresholds”:
**40+ kt** suggests:  if storms develop -- supercells are likely (provided convective mode favors cellular activity)
**30-40 kt**:  supercells also possible if environment is very or extremely unstable as storm can augment local shear (>5,000 J/kg (Burgess (2003))
- About **15-20 kt:****  **shear needed for organized convection (multicell or supercell) with mid level winds at least 25 kt
- While 0-6km shear is a good discriminator between cell types, it isn’t a good tornado forecast tool (Thompson et al, 2002).

## 0-6 km Shear Magnitude

- Supercells
- Non-Supercells

- From Thompson et al (2002)

## BRN Shear

- (Weisman and Klemp (1982), and Thompson (2000 &2002)

- BRN Shear is the vector difference between the density weighted mean winds in the lowest 6 km and the lowest 500 m above ground level.   BRN shear can be a used as a good predictor of storm type and severity.

- Supercells
- Non-Supercells

- From Thompson et al (2002)

- 40 m2/s2
- 35 m2/s2

## Supercell Composite Parameter (Thompson et al, 2003)

- The Supercell Composite Parameter (SCP) is a multi-parameter index that includes 0-3 km SRH, CAPE, and BRN Shear. Each parameter is normalized to supercell “threshold” values.
- SCP = (muCAPE/1000 J/kg) * (0-3km SRH/100 m**2/s**2) * (BRNShear/40 m**2/s**2)
- Computed every hour on the SPC Mesoanalysis Page.

## Supercell Composite Parameter (Thompson et al, 2003)

- May 4th, 2003

## What Causes Supercell Type

- Rasmussen and Straka (1998) found in an observational study of 43 isolated supercells that supercell type is much more dependent precipitation efficiency based on its ingestion of hydrometeors.

## Classic Supercells

- The real “value” of a CL supercell is that it appears to be the most efficient of the three types to produce significant tornadoes.
- Can occur nearly anywhere in U.S. when NSE supports them.

## High Precipitation (HP) Supercells

## High Precipitation (HP) Supercells

- Lower mid-level and anvil-relative flow.
- Interactions with other storms – “seeding”, more storms can occur with weak caps.
- Typically associated with weaker tornadoes, but can produce significant tornadoes (Plainfield IL).
- More of a severe wind (Pakwash), hail, and flash flooding threat.
- Are the more-common supercell type east of the Mississippi owing to NSE conditions there (weaker caps, etc.), and may be the most common type everywhere in the U.S.

## Supercell Dimensions

- Burgess (2003)

## Supercell Movement

- Bunkers et al (2000)

- A physically based, shear-relative, and Galilean invariant method based on 290 supercell hodographs.

## Supercell Movement

- Bunkers and Zeitler (2000)

- There are some caveats to this method:
- Stronger deep-layer vertical wind shear (0-6 km) leads to a stronger mesocyclone and thus to greater deviation from the mean wind.
- Weaker mid-level storm-relative winds allow for a stronger cold pool, and thus a tendency for the supercell to move rapidly downshear.
- Depth of thunderstorms need to be considered.
- Supercell motion can be altered by wind shear from boundaries and orography.

## Storm Coverage and Mode

- What’s the Problem?
- Evans (2003) noted Strong Forcing Derechoes and discrete, significant tornadic supercells (F2-F5) can occur in similar environments.
- Unfortunately, differences can be very subtle and difficult to diagnose operationally.

## What Controls Storm Coverage?(Thompson, 2004)

- Widespread coverage expected with:
- Rich moisture influx and steep lapse rates
- Combination of Q-G and mesoscale ascent
- (Differential CVA and WAA with surface frontogenesis)
- Little CIN  (Everything goes up.)
- Isolated (or no) storms with:
- Marginal moisture and lapse rates (weak CAPE)
- Neutral to subsident large-scale environment (Rely on small-scale/shallow processes for initiation)
- Large CIN (Confine storms to “strongly forced” or in  areas of most persistent ascent)

## What Causes Convective Mode?

- _Discrete_                          _Squall Line_

- weaker
- more
- weaker
- more perpendicular

- stronger and/or deeper (or confined near boundary)
-  less
- greater
- more parallel

- Strength and Depth of Boundary Forcing
- Amount of CIN compared to Boundary Forcing
- Potential for Cold Pool Shear Vector w.r.t. Boundary Orientation

## Initiating Boundary w.r.t. Deep Layer Flow (Bluestein and Weisman, 2000; Dial and Racy, 2004)

- Parallel: (lines dominate, with end supercells)
- 45o:  (discrete supercells, little storm interaction)
- 90o: (colliding storm splits, but depends on storm spacing and hodograph shape)

## Progressive Trough

- 0-6 km shear across dryline, and storm motion faster than boundary motion

- From Rich Thompson, SPC

- May 4th 2003 Tornado Outbreak, Progressive Flow Aloft

## High Amplitude Trough

- 0-6 km shear largely parallel to
- dryline, and storm motion slower than boundary motion

- From Rich Thompson, SPC

- April 6th 2001 Great Plains “High Risk” Squall Line

## Derechoes or Tornadoes?

- Anvil SR Winds may show some discrimination (Evans 2003).

## Surface Pressure Changes

- 1-2 hourly pressure changes help identify:
- Mesolow /mesohigh couplets and boundaries
*Concentrated fall/rise couplet enhance low- level convergence/shear by backing surface winds (enhancing tornado threat)*
- Clouds associated with surface pressure falls may be linked to a dynamical feature
- Implications on thermal advection
- Rise/Fall couplets may indicate severe wind threat in marginal CAPE environments

## Convective Severity

|  | Dmg winds | Hail | Tornado | FF |
| --- | --- | --- | --- | --- |
| Ordinary cell
(0-6km shear <15 m/s) | Steep LL lapse rates
High LCL, dry midlevels, high DCAPE
Intense elevated core
Descending core bottom
Elevated radial convergence | Cold temps aloft
Large buoyancy ~
-20 C
Intense elevated core ~ -20 C and colder
High VIL density, TBSS | No CIN, steep LL lapse rates
Sharp boundary with LL vertical vorticity
Rapidly growing and new CBs  | high RH in deep layer; deep warm cloud; small mean wind 
Slow storm motion 
Large storm core |
| Super-cell
(0-6km shear > 15 – 20 m/s) | Similar environ as above except for shear and high CAPE & DCAPE, strong 0-1 km shear can assist
In addition to above, LL mesocyclogenesis; developing hook, deep convergence zone | Large buoyancy @-20 C level, strong 0-6 km shear, stg mid- upper SR flow; 
WER BWER, intense elevated core,
mesocyclone,
TBSS, high VIL density | Strong 0-1km shear in addition to 0-6 km shear; low LCL; low CIN
LL TVS, meso, inflow notch; sign of a hook, strong LL convergence below mesocyclone; BWER | High RH in deep layer; deep warm cloud; small SR anvil flow
Low supercell motion
Not an LP storm |
| Multicell
(organized group of ordinary/supercells) | >40kt 0-6km shear
Strong >30kt 700-500 wind;
Stg leading  Gradient;
Bookend vortex pair;
MARC, deep convergence zone, rear inflow notch | Separated cores; cells exposed to favorable environment | Similar to supercells?  
Mostly left of rear inflow notches along leading edge of core, front inflow notch with WER and vert vorticity | Slow MBE motion; triple pt anchoring; upwind instability, LL jet, high PW, high mean RH
Intrastorm seeding
Echo training, slow motion |

- From DLOC “Hazards Assessment”

## Tornado Parameters

- Mesocyclonic Tornadoes
- Low Level Shear Vector and Storm Relative Helicity
- Low Level Thermodynamic Profile
- Height of LCL
- Height of LFC
- Low Level CAPE and CIN
- Boundaries
- Non-Mesocyclonic Tornadoes

## 0-1km Shear Vector

- Brooks and Craven (2002)

- Supercells associated with significant tornadoes
- Non-Tornadic

- 20 kts
- 15kts

- Markowski et al (2002) states this is a measure of the amount of horizontal vorticity available near the earth’s surface.
- The shear magnitude in the lowest 1 km discriminates well between tornadic and non-tornadic supercells, and is a good proxy for 0-1km helicity (Thompson et al, 2002).
- Does not require knowledge of storm motion.

## 0-1km Storm Relative Helicity

- Supercells associated with significant tornadoes
- Non-Tornadic

- Thompson et al (2002)

- SRH can vary up to two orders of magnitude within 100km and 3 hrs.
- No good threshold, but 100 m2/s2 is considered a good lower number with increasing threat as the numbers grow. Outbreaks 200-300 m2/s2. (Rasmussen and Blanchard, 1998 and Thompson et al, 2002).

## 0-1km Storm Relative Helicity

- From Banacos (2003)

- May 4th, 2003

- April 22nd, 2004

- From Jon Davies Webpage

## Height of the LCL (Mean Layer)

- Markowski (2000) speculates that lower LCL heights mean high boundary layer RH and increased buoyancy in the RFD.

## Height of the MLLCL

- From Brooks and Craven (2002)

- From Thompson et al (2002)

## Let’s Take a Look

- Classic supercells which produced several strong tornadoes.

## Height of the LFC

- Why is this important?
- Lower LFC’s (below 2km or 750mb) have more instability above the LFC and less CIN above that higher LFC’s.
- Lower LFC’s require less lift for the parcel to reach convective initiation
- In a study of over 300 soundings associated with supercells, most tornadoes are found with LFCs below ~6,600 ft, though may occur as high as ~7900 ft with large amounts of vertical shear. (Davies, 2002)
- Rasmussen and Blanchard (1998) found that 75% of tornadic classic supercell environments had CIN <25-50 J/kg) and 60% of non- tornadic supercell environments had values greater than this

## Let’s Take a Look

- Several supercells, one producing a F3 tornado.

## Let’s Take a Look

- Several classic supercells along I-44, including a F3.

## Let’s Take a Look

- Several supercells in central MO, producing F2 tornadoes.

## What About Boundaries?

- Boundaries serve two important functions:
- Local forcing mechanisms for convective initiation.
- As a source of vorticity augmentation in mesocyclones.
- Significant tornadoes usually require higher quantities of SRH than is normally provided.  They often require augmentation from boundaries.  (Markowski et al (1998a))

## Forward Flank Downdraft

- Streamwise vorticity occurs along the boundaries of the FFD.
- Parcels generally only acquire 0.001 s–1 shear because of small residence times.
- For FFD boundaries to be the primary source of streamwise vorticity, it is speculated that the environment must be highly helical (I.e. SRH > 500 m2 s–2 or 0-10 km shear of ~100 kts per Markowski et al (1998b).

## Outflow From External Thunderstorms

- Rasmussen (2000)

_**“**__**Cool”**__** side of outflow boundaries:**_
-  Look for modified outflow (>6 hrs old) where there’s sunshine and growing CAPE (a.k.a. “cooked” outflow), and surface dewpoints are great than the warm sector.   .

## Boundaries

- Markowski et. al. (1998b)

- Tornadic development most likely from 10 km on warm side of boundary to 30 km on cool side of boundary.

## Local Example

- May 6, 2003

## Local Example

- April 21, 2002

- From of  Fred Glass

## Anvil Boundaries 

-   Requires limited cloud coverage around periphery of storm.
-   May be more important than the FFD because of much long parcel residence times in the boundary depending on the inflow vector.

- Preferred direction for longer parcel residence times.

## Significant Tornado Parameter (Thompson et al, 2003)

- The Significant Tornado Parameter is a multi-parameter index that includes 0-6-km shear magnitude, 0-1km storm-relative helicity, 100-mb mean parcel CAPE, and 100-mb mean parcel LCL height.
- SCP =(mlCAPE/1000 J/kg) * ((2000 -mlLCL)/1500 m) * (SRH1/100 m**2/s**2) * (SHR6/20 m/s)
- Computed every hour on the SPC Mesoanalysis Page.

## Significant Tornado Parameter (Thompson et al, 2003)

- May 4th, 2003

## Non-Supercell Tornadoes

- Typically associated with ordinary cells
- No CIN
- Steep low level lapse rates
- Sharp boundary with low level vertical vorticity.
- Rapidly developing CBs

## Non-Supercell Tornadoes

- From Wakimoto and Wilson (1989)

- May 25, 1997

## Wind Parameters

- Microbursts
- Bow Echoes and Derechoes

## Microbursts

- Atkins and Wakimoto (1991) found “wet” microbursts occurred on days when the delta theta-e between the surface and mid-levels is _>_20K.   Null days occurred when this value is _<_13K.
- Dry microburst tend to occur with high LCLs and steep low level lapse rates.

## Bow Echoes and Derechoes

- 	Bow echoes and derechoes are associated with moderate to strong shear in the low levels (Przybylinski, 2001):
- <23 kts:  Weak Shear (Bow echoes less likely)
- 22-37 kts:  Moderate Shear (Bow echoes likely with the greatest threat of damaging winds)
- >37 kts:  Strong Shear (Bow echoes likely with strongest winds remaining above the surface.

## Bow Echoes...Typical Morphologies

**Bow Echoes...Typical Morphologies**

**Bow Echo**

**Squall Line Bow Echo**
**(LEWP)**

**Cell Bow Echo**

**Bow Echo Complex**

**Bow Echo**

**Supercell**

**Notes:**
Many different shapes and sizes to bows
Main Question is....how did these storms come about?
	Why did this squall line develop bowing structures at these two specific places?
	Is the predictability of one type of bow greater than another?

## Forward Propagating MCS 

## Forward Propagating MCS 

- Low Level Boundary

## Back-building and Quasi-Stationary MCSs

## ‘Classic’ Bow EchoWind Shear Profiles (Hodographs)

## Elevated Hail Storms

- Steep mid level lapse rates (850 –500 mb lapse rates 7 deg C/km or greater)
- MUCAPE > 1000 J/kg
- Large CAPE in the -10 to -30oC /-20 to -40oC range on a sounding
- Strong deep shear (through mean cloud layer wind)
- Minimized melting effects (lower Freezing levels , WBZ < 10K ft)

## Surface Based Storms

- Mid level updraft rotation (need enough deep shear > 35 kts  between 0-6 km AGL)
- Need steep lapse rates , sufficient low-level moisture, sufficient lifting mechanism (related to CAPE in hail growth zone)
- Note: in absence of 1., greater dependence on 2.)

## Supercell Hail Forecasting

- Large CAPE in the layer from -20 to-40oC (-10 to -30oC) favors rapid hail growth.
- 0-6-km shear in excess of 30-40 knots supports supercells with persistent updrafts that contribute to large hail production
- Lower freezing level heights suggest a greater probability of hail reaching the surface prior to melting

## Hail Forecasting Parameters

- “Hail Parameters” depicts three forecasting parameters used to predict hail. They are CAPE in the layer from -20 to -40oC, 0-6-km shear vector, and the freezing level height.
- The Sig. Hail Parameter (SHIP) was developed using a large database of surface-modified, observed severe hail proximity soundings to determine the potential of hail _>_2" diameter.
- 	SHIP = [(MUCAPE j/kg) * (Mixing Ratio of MU PARCEL 	g/kg) * (700-500mb LAPSE RATE c/km) * (-500mb 	TEMP C) * (0-6km Shear m/s) ] / 44,000,000
- Both are computed every hour on the SPC Mesoanalysis Page.

## Summary

- Steps for severe weather forecasting:
- Will I have TSRA?  (Moisture, Instability, and Forcing)
- What will be my primary convective mode and coverage?  (Instability, Shear, and Forcing)
- What kind of severe weather will I have?   (Tornadoes, Hail, Winds)

## References

- 	Atkins, N.T. and R.M. Wakimoto, 1991:  Wet Microburst Activity over the Southeastern US:  Implications for Forecasting. Wea.  Forecasting, **6**, 470-482.
- 	COMET Forecaster’s Multimedia Library, 1996:  Anticipating convective storm structure and evolution.
- 	Bluestein, H.B. and M.L. Weisman, 2000:  The interaction of numerically simulated supercells initiated along lines.  Mon. Wea. Rev., **128**, 3128-3149.
- 	Banacos, P.C., 2003: **Severe Weather Threat Assessment.  Presentation at the, *****WDTB Severe Weather/Flash Flood Workshop Course 03-4, *****Boulder, CO.**
- 	Brooks, H. E., and J. P. Craven, 2002: A database of proximity soundings for significant severe thunderstorms, 1957-1993. *Preprints*, 21st Conference on Severe Local Storms, San Antonio, Texas, American Meteorological Society, 639-642.

## References

- Burgess, D.W., 2003: Supercells.  Presentation at the COMAP Course, Boulder, CO.** **
- Burgess, D.W. and L.R. Lemon, 1991:  Characteristics of Mesocyclones Detected During a NEXRAD Test.  Preprints, 25th Int. Conf. On Radar Meteorology, Paris, France, AMS, 39-42.
- Craven, J. P., 2000:  A Preliminary Look at Deep Layer Shear and Middle Level Lapse Rates Associated with Major Tornado Outbreaks. Preprints, 20th Conference on SLS, Orlando, FL, AMS, 547-550.
- Davies, J. L., 2004:  Tornadoes in a Deceptively Small CAPE Setting:  The "Surprise" 4/20/04 Outbreak in Illinois and Indianahttp://members.cox.net/jondavies3/042004ilin/042004ilin.htm
- Davies, J. L., 2002:  A Primer on Low-level Buoyancy Parameters When Assessing Supercell Tornado Environments. http://home.kscable.com/davies1/LLbuoyprimer/LLbuoyprimer.htm

## References

- Dial, G.L. and J.P. Racy, 2004: Forecasting Short Term Convective Mode and Evolution For Severe Storms Initiated Along Synoptic Boundaries. Preprints, 22nd Conference on SLS, Hyannis, MA, Amer. Meteor. Soc..
- Evans, J. and C. Doswell, 2003:  Presentation given to WFO Tulsa Staff.http://www.spc.noaa.gov/staff/evans/talk4/talk4_frame.htm
- Edwards, R., 2000:  Personal Communication.
- Edwards, R. and R. L Thompson, 2000:  RUC-2 Supercell Proximity Soundings, Part II:  An Independent Assessment of Supercell Forecast Parameters. Preprints, 20th Conference on SLS, Orlando, FL, AMS, 236-239.
- Klimoski, Brian A. and R. W. Przybylinski, 2003:  Observations of, and Forecasting the Formation and Early Evolution of Bow Echoes.  Presentation at the COMAP Course, Boulder, CO.
- Lanicci, J. and T. Warner, 1991: A synoptic climatology of the elevated mixed- layer inversion of the southern plains.  Part I: Structure, dynamics, and seasonal evolution.  Wea.  Forecasting, **6**, 181-197.

## References

- Markowski, P. M., C. Hannon, J. Frame, E. Lancaster, A. Pietrycha, R. Edwards, and R Thompson, 2002:  Characteristics of RUC Vertical Wind Profiles Near Supercells. Preprints, 21st Conference on SLS, San Antonio, TX, AMS, 599-602.
- Markowski, P. M., E. N. Rasmussen, and J. M. Straka, 1998a: The occurrence of tornadoes in supercells interacting with boundaries during VORTEX-95.  Wea.  Forecasting, **13**, 852-859.
- Markowski, Paul M., E. N. Rasmussen, J. M. Straka, D. C. Dowell, 1998b: Observations of Low-Level Baroclinity Generated by Anvil Shadows. Monthly Weather Review: Vol. 126, No. **11**, pp. 2942–2958.
- Markowski, P. M., E. N. Rasmussen, and J. M. Straka, 2000:  Surface Thermodynamic Characteristics of RFDs as Measured by a Mobile Mesonet. Preprints, 20th Conference on SLS, Orlando, FL, AMS, 251-254.

## References

- Przybylinski, R.W., 2001:  Personal Communication.
- Rasmussen, E. N., and D. O. Blanchard, 1998: A Baseline Climatology of Sounding-Derived Supercell and Tornado Forecast Parameters.  Wea.  Forecasting, **13**, 1148-1164.
- Rasmussen, E.N., S. Richardson, J.M. Straka, P. M. Markowski, and D. O. Blanchard, 2000: The association of significant tornadoes with a baroclinic boundary on 2 June 1995.  Mon. Wea.  Rev., **128**, 174-191.

## References

- Rasmussen, E.N, and J. M. Straka, 1998: Variations in supercell morphology.  Part I: Observations of the role of upper-level storm relative flow.  Mon. Wea. Rev., **126**, 2406-2421.
- Thompson, R. L., 1998: Eta model storm-relative winds associated with tornadic and nontornadic supercells.  Wea.  Forecasting, **13**, 125-137.
- Thompson, R.L., 2000:  Personal Communication.
- Thompson, R.L., R. Edwards, and J.A. Hart, 2002:  An Assessment of Supercell and Tornado Parameters with RUC-2 Model Close Proximity Soundings. 21st Conference on SLS, San Antonio, TX, AMS, 595-598.
- Thompson, R. L., 2004.  Presentation: Forecasting Thunderstorm Coverage and Configuration

## References

- Thompson, R.L., C.M. Mead, and R. Edwards, 2004: Effective Bulk Shear in Supercell Thunderstorm Environments. *Preprints*, 22nd Conf. Severe Local Storms, Hyannis MA
- Thompson, R.L., R. Edwards, and C.M. Mead, 2004: Effective Storm-Relative Helicity in Supercell Thunderstorm Environments. *Preprints*, 22nd Conf. Severe Local Storms, Hyannis
- Thompson, R. L., R. Edwards, J. A. Hart, K. L. Elmore, and P. Markowski, 2003:  Close proximity soundings within supercell environments obtained from the Rapid Update Cycle. *Wea. Forecasting, ***18**, 1234-1261*.*
- Wakimoto, R.M., and J.W. Wilson, 1989: Non-Supercell Tornadoes. *Mon. Weather Rev.*, **117**, 1113-1140.
- Weisman, M. L., and J. B. Klemp, 1982: The Dependence of Numerically Simulated Convective Storms on Vertical Wind Shear and Buoyancy.  Mon.  Wea.  Rev., **110**, 504-520.