# Presentation: 859146

## Verification of a Hail Warning Criteria and its Usefulness Across the Northern and Central Plains

- Rod Donavon
- National Weather Service
- Des Moines, IA  (DMX)
-                  The views expressed are those of the author and do not necessarily represent those of the National Weather Service.

## Quick Review

- _[http://www.crh.noaa.gov/fgf/science/science.shtml](http://www.crh.noaa.gov/fgf/science/science.shtml)_
- Use of All Tilts product most useful
- Radar Operator can view storm structure and make decisions before derived products become available.
- Allows Radar Operator to view all available elevation slices within the  current Volume Scan in Real Time. (Availability dependant on RPS list)
- Can give idea of updraft strength and hydrometeor potential based on reflectivity heights.

## Data Used For Study

- Storm Data
- Local and Model Soundings and NCDC Freezing Level Charts
- Archived Radar Data
- Correlated 50-55 dBZ reflectivity echo heights (AGL) with associated hail reports and FZLs (MSL)
- Heights obtained using elevation scans and not with cross sections. (Only base data used, derived data not as reliable)

## WSR-88D Build 9 Hail Detection Algorithm (HAD)

- Klimowski, B., S. Vasiloff and A. Witt, (1997)
- POH compared the top of the 45 dBZ echo to the Freezing Level.
- POH = 100% when the top of the 45 dBZ echo extended more than 18000 ft above the Freezing Level.
- The algorithm looks specifically for “elevated cores”

## Techniques for Issuing Severe Thunderstorm and Tornado Warnings with the WSR-88D Doppler Radar 

- NOAA Technical Memorandum (1997)
- The height of the 50 dBZ echo generally applies to warning criteria for hail
- Lemon suggests 50 dBZ to 27000 ft AGL is needed for severe, could be lower if weak echo region detected.
- During the summer, this may extend to 35000 ft AGL or greater

## Updraft Strength (Lemon 1977, 1980)

- In general, storm severity is determined by updraft strength.
- Updraft strength can be related to the storm’s echo top height and peak reflectivity
- This research concentrates on the 50 dBZ echo height as an updraft strength indicator and the potential for storm severity.

## FGF DATA ONLY

**FGF DATA ONLY**

## Warning Criteria Used at FGF

**             **_**FZLVL(MSL)**_**       ****	****	****     **_** Warning Criteria (AGL)**_** **
**                ****7000 ft****	****	****	****	****15000 ft****	****    ****	****        ****	**
**                ****7500 ft****	****	****	****	****16000 ft**
**                ****8000 ft****	****	****	****	****17000 ft****	****                      **
**                ****8500 ft ****	****	****	****	****18000 ft****	****	****	****      **
**                ****9000 ft****	****	****	****	****19000 ft****	****     ****	****        **
**                ****9500 ft****	****	****	****	****20000 ft****	****	****	**
**              ****10000 ft****	****	****	****	****21000 ft****	****     ****	****        ****	**
**              ****10500 ft****	****	****	****	****22000 ft****	****	****	****      **
**              ****11000 ft****	****	****	****	****23000 ft****	****     ****	****        **
**              ****11500 ft ****	****	****	****	****24500 ft****	****	****	**
**              ****12000 ft****	****	****	****	****26000 ft****	****     ****	****       **
**              ****12500 ft****	****	****	****	****28000 ft**
**              ****13000 ft****	****	****	****	****30500 ft****	****      ****	****        **
**              ****13500 ft****	****	****	****	****33000 ft****	**
**              ****14000 ft****	****	****	****	****35500 ft****	****      ****	****        **
**              ****14500 ft****	****	****	****	****37500 ft**
**              ****15000 ft****	****	****	****	****40000 ft****	****     ****	****        **
**              ****15500 ft****	****	****	****	****42000 ft****	****	****        **

## For Min Warn Criteria, want at least this strong of a 50-55 dBZ echo. 

## FZLVL = 12500 ft MSL50 dBZ echo height 28000 ft AGL

## Slide 11

## 36100 ft

**1.25” Hail**

**19900 ft**
**No Report**

## 55-60 dBZ

**34600 ft**
**2.00 “ Hail**

## 65-70 dBZ

**21600 ft**

**25400 ft**
**No Report**

## Slide 15

## 55-60 dBZ

**38000 ft**
**1.75” Hail**

## 70-75 dBZ

**13800 ft**

**65-70 dBZ**
**27300 ft**

## 33400 ft

**No Report**

**60-65 dBZ**
**31000 ft**
**2.00” Hail**

**29200 ft**
**0.75” Hail**

## 30600 ft

**0.88” Hail**

## 65-70 dBZ

**27700 ft**
**1.00” Hail**

## Verification of Warning Criteria at FGF 2003

- Worked very well
- There were 354 wind and hail events
- High Probability of Detection POD = 0.924
- Low False Alarm Rate  FAR = 0.163
- CSI = 0.783
- Average Lead Time = 20.0 minutes
- 13 missed hail events – only 3 were missed by the warning criteria

## Notes from FGF 2003

- Most Storms that met borderline criteria contained hail with a small areal coverage of severe hail (0.75 in or greater)
- The more persistent the updraft, the larger the areal coverage of severe hail.
- The majority of Pulse Storms that met criteria for only one volume scan, contained 0.75 inch hail...though over a very small area.

## Notes from FGF 2003 Cont.

- Very good chance of severe hail once severe criteria exceeded by 2000 ft, often times 1.00 inch hail was present when exceeded by 3000 ft.
- Pulse severe storms detected with a 5-10 minute lead time.  Generally a 20 minute lead time achieved with Multicells and Super Cells.
- Cells with an elevated 65 dBZ core were almost always severe.

## Evolution of a Pulse Storm with an Elevated 65 dBZ Core

## Intense updraft evident with 55 dBZ present at 26000 ft AGL

## Elevated 65 dBZ Core Present

**Appears to be weakest storm at 0.5 Degrees**

## Notice the 65 dBZ core descending though the 3.4 and 4.3 slices

## 65 dBZ core has descended to the 0.5 degree slice

**0.88 inch hail is reported 4 minutes later**

## Comparing FGF and DMX Data

- Roughly same topography and elevation across both County Warning Areas (CWA)
- Typically more elevated thunderstorms across the FGF CWA while more low level moisture available across DMX CWA
- Lower Criteria needed for the FGF CWA due to less melting taking place????????
- DMX has some outliers at Freezing Levels >13000 ft MSL.  Any reason for this???

## Topography

## These 2 had elevated 70+ dBZ cores to 13000 ft

**These 2 had elevated 70+ dBZ cores to 13000 ft**

**Elevated 65+ dBZ cores **
**> 25000 ft.**

## Slide 32

## Preliminary 50-55 dBZ Echo Heights for Severity and Size Potential

_**FZLVL(MSL)**_**       **_**Minimum Warning Criteria**_**   **_**1.25-2.0 inch**_**	****   **_**> 2.0 inch **_
**7000 ft****	****	****15000 ft****	****    ****	****        19000 ft****	**
**7500 ft****	****	****16000 ft**
**8000 ft****	****	****17000 ft****	****                       21000 ft**
**8500 ft ****	****	****18000 ft****	****	****	****      **
**9000 ft****	****	****19000 ft****	****     ****	****        23000 ft**
**9500 ft****	****	****20000 ft****	****	****	****	**
**10000 ft****	****	****21000 ft****	****     ****	****        25500 ft****	**
**10500 ft****	****	****22000 ft****	****	****	****      **
**11000 ft****	****	****23000 ft****	****     ****	****        28500 ft****	****     36000 ft**
**11500 ft ****	****	****24500 ft****	****	****	****	**
**12000 ft****	****	****26000 ft****	****     ****	****        32000 ft****	****     39000 ft**
**12500 ft****	****	****28000 ft**
**13000 ft****	****	****30500 ft****	****      ****	****        36000 ft****	****     42000 ft**
**13500 ft****	****	****33000 ft****	**
**14000 ft****	****	****35500 ft****	****      ****	****        40000 ft****	****     46000 ft**
**14500 ft****	****	****37500 ft**
**15000 ft****	****	****40000 ft****	****     ****	****        44000 ft****	****     50000 ft**
**15500 ft****	****	****42000 ft****	****	****        **
**NOTE:  Any storm exceeding Minimum Warning Criteria by 2000 ft **_**should**_** be warned for.  A small area of 0.75 in hail is likely up to this threshold.**

## Slide 34

## Freezing Level and Wet Bulb Zero Relationship

- Some affect noticed when difference greater than 1500 ft
- Most noticeable when difference exceeded 2000 ft. Especially with storms containing very large hail or when near storm environment was altered by previous storms
- In these cases, FZLVL likely lowered due to evaporative cooling through the column

## Forecast Soundings FZL >> WBZ

## FZLV >> WBZ Continued

**Good fit if FZLVL had fallen to Wet Bulb Zero Height**

## Other Updraft Strength Identifiers to Keep in Mind

- Weak Echo Region (WER)
- Strong Storm Top Divergence
- Elevated 65 dBZ echo
- Height of the 60-65 dBZ echo useful for storms close to the RDA.

## Davison Co. SD, June 24, 2003

## Slide 40

## Slide 41

## Slide 42

## Slide 43

## Slide 44

## Slide 45

## Summary

- The test warning criteria worked very well at FGF during the 2003 convective season
- A correlation is apparent between FGF and DMX hail data.
- Hail size can be estimated using this process and the 50 dBZ height is a good indicator of updraft strength.
- An elevated 65 dBZ core above 25000 ft will tend to supercede the 50-55 dBZ height criteria when FZLV > 13500 MSL.
_**Should**_** **use as a warning basis at the higher FZLVLs even when the 50-55 dBZ height is not being met.

## Summary Continued

- Be aware of the Near Storm Environment, i.e. cold pool moving in or potential for evaporative cooling through the column.
- NSE especially important when large differences exist between the Freezing Level and Wet Bulb Zero Heights.
- Often the second or third storm through an area over a short period of time, will have a lower threshold due to above processes.

## Questions or Comments???

- rodney.donavon@noaa.gov
- NWS Des Moines, IA (DMX)