1. Use of the ALY Hail Study to Predict Large Hail During the 21 July 2010 Severe Weather Event
Brian J. Frugis and
Thomas A. Wasula
NOAA/NWS Albany, New York
NROW XII
3-5 November 2010

2. 1” Hail Project Motivation and Evolution
The minimum criteria for severe hail was raised from 0.75 in. (1.9 cm) to 1.00 in. (2.5 cm) on 5 January 2010
Continuation of a project that began in the Fall of to focus on warning strategies using this new criteria
Was presented at the 11th Northeast Regional Operational Workshop (NROW) at UAlbany in November 2009, The Eastern Region Severe Weather and Radar Workshop in June 2010 in Virginia, and the 3rd Tri State Weather Conference in October 2010 in Danbury, CT

3. 1” Hail Project Collaborators
Is a CSTAR IV sub-project under the Deep Convection and Severe Weather Research Topic
Data analysis done by Tom Wasula and Brian Frugis
Albany (ALY) SCEP Student Rihaan Gangat has been helping with the data analysis and data entry
ALY STEP Student Rebecca Darrow helped evaluate some of the preliminary statistical data

4. Data Used in the Study
Examined hail reports from minor and major events from
Used data from LSR reports that were entered into StormData
Original NROW XI study had only 70 hail reports in database
Database as of Sept contained 336 hail reports
Hope to have all hail reports from the ALY area from the advent of the 8 bit radar data in the database by the end of 2010
Some of the earlier archives from have limited radar data, so assessing each parameter has been difficult for some of the reports

5. Events Used for Hail Study
2010
2009
2008
2007
2006
2005
TOTAL
July 17-18
June 15
June 10
May 10
May 30-31
June 6
July 21-22
June 26
June 16
May 31
June 1
July 7
June 22-24
June 5
June 29
July 16
July 26-27
June 19
Sept 9
July 26
Aug 7
Aug 3
Total Severe Reports 14 52 57 32 4
163
Total Hail Reports 27
101
115 9
336

6. Parameters Examined for Each Hail Report
50, 55, 60 and 65 dBZ Echo Top (ET)
The height of the 50 dBZ above the -20° C isotherm was also calculated
Gridded VIL and Storm Echo Top
VIL Density was also calculated using the above values
Wind Damage?
Assigned a Y/N Flag to whether wind damage was also associated with this storm cell
SCAN program calculations
Cell-based VIL and maximum hail size
Storm type
Multi-cellular, pulse or supercell
Freezing Level and -20° C Height
Based on most recent KALB sounding or closest adjacent site if KALB was unavailable

7. Other Data from Events Freezing Levels ranged from 8.9 – 14.3 kft
-20° C Heights ranged from 18.5 – 25.6 kft
Hail sizes were from 0.25” to 2.60”
The county with the most hail reports was Albany (57 reports)
The county with the least hail reports was Warren (3 reports)
76% of storms were multi-cellular
22% were supercell and 2% pulse

8. Methodology for Determining dBZ ET Values
Use of the FSI 4D Storm Investigator was used extensively
The Vertical Slice Image was used to get an idea where the ETs for the various dBZ level would be and the CAPPI was utilized to find specific values
A severe storm in Litchfield County, CT during the July 19, 2009 event

9. Methodology for Determining Gridded VIL and Storm ET Values
Used the highest VIL/Echo Top value over the location of the storm report within +/- 1 volume scan of report time
Midpoint value for VIL or ET square was used
Except when specific value was known due to being maximum value on screen
High VIL Values from a storm near Lake George from August 25, 2007

10. Severe vs. Non-Severe Hail
0.25”- 0.88” (Nickel or smaller) Hail
1.00”+ (Quarter or Larger) Hail
Difference
Avg Height of 50 dBZ Echo Top
27.7 kft
31.2 kft
3.5 kft
Avg Height of 50 dBZ Echo Top above -20° C Isotherm
5.7 kft
9.0 kft
3.3 kft
Avg Gridded VIL
(kg/m2)
45 kg/m2
51 kg/m2
6 kg/m2
Avg VIL Density (g/m3)
3.82 g/m3
4.08 g/m3
0.26 g/m3

11. Severe vs. Non-Severe Hail
” (Nickel or smaller) Hail
1.00”+ (Quarter or Larger) Hail
Difference
Avg Height of 55 dBZ Echo Top
23.6 kft
27.7 kft
4.1 kft
Avg Height of 60 dBZ Echo Top
18.4 kft
23.4 kft
5.0 kft
Avg Height of 65 dBZ Echo Top
13.4 kft
18.6 kft
5.2 kft

13. Critical dBZ Echo Tops using Median Values for Warning for Severe Hail (severe = 1” or greater)
50 dBZ Echo Top reaching over 31.0 kft
55 dBZ Echo Top reaching over 28.1 kft
60 dBZ Echo Top reaching over 24.2 kft
65 dBZ Echo Top reaching over 18.7 kft
These median values are also very close to the mean (average) values for each respective level
25th percentile numbers can also be used as a “cautionary value” for warning purposes
50 dBZ = 27.0 kft, 55 dBZ = 23.4 kft,
60 dBZ = 18.0 kft, 65 dBZ = 11.8 kft

14. Overview of 21 Jul 2010 for ALY CWA
9 severe hail reports
Largest was 1.75” in Litchfield County, CT
34 wind damage reports
EF0-EF1 Tornado Damage (in Litchfield County, CT)
KALB 18 UTC Sounding
FZL level =13.2 kft
WBZ level = 11.2 kft
-20° C level =23.2 kft

15. Regional Radar Mosaic from 21 July 2010
Imagery courtesy of Neil Stuart, NWS Albany

16. Litchfield, CT Supercell Storm Reports
First produced severe hail around UTC
Additional severe hail UTC
Wind damage and UTC
Tornado from UTC in ALY area

17. FSI-4D Storm Investigator at 1902 UTC
Volume scan just prior to first report of hail
50 dBZ reach above kft
65 dBZ reach well above kft
CAPPI set to -20° Celsius level

18. KENX VIL and Echo Top Images at 1902 UTC
Max VIL value of 61 kg/m2 and Max ET value of 47 kft
VIL Density computed to be 4.26 g/m3
Hail Study Average values are a VIL of 51 kg/m2 and a VIL Density of 4.08 g/m3

19. Other Indications of Severe Hail
SCAN software shows max hail size of 2.75 inches and VIL over critical value of 51 at 1934Z just prior to second burst of severe hail
SCAN correctly predicted severe hail 75% of the time in the ALY hail study
Hail spike located at several levels on KENX radar at 1943Z

20. KENX Cross Section at 1943 UTC
50 dBZ (red color) still well exceeding 31.0 kft
65 dBZ (dark pink color) as high as kft
70+ dBZ (dark purple color) over 20.o kft
Hail core appears to be reaching surface
Several reports of golf ball sized hail shortly after this time in eastern Litchfield County

21. Berkshire County Supercell
Produced one report of wind damage (two trees down) in Pittstown, NY (north-central Rensselaer County) at 1754Z
Storm showing supercell characteristics but not overly tall
Must make warning decision as storm approaches Berkshire County around 1816 UTC

22. FSI 4D Storm Investigator at 1824 UTC
Volume scan just when storm was entering Berkshire County
50 dBZ (red) only reached 25 kft (not even “cautionary value” in the study)
60 dBZ (white) only reached 18 kft
These values would decrease confidence for warning for severe hail
ALY Hail Study average top of 50 dBZ for severe hail

23. VIL and Echo Top at 1816 UTC Max ET values of 40-45 kft
VIL Density = 3.28 g/m3
Max VIL values kg/m2
Hail study avg. severe VIL = 51 kg/m2
Hail study avg. severe VIL Density = 4.08 g/m3

24. Storm Reports from Berkshire County
Storm only produced pea to half-inch size hail in Berkshire County
One tree reported down at UTC
Gust to 43 mph at KAQW
Severe warning did not verify for Berkshire County
Supercell held together across central Massachusetts and prompted a tornado warning from BOX
Storm produced wind damage and severe hail (up to inches) in central Mass.

25. Applications of Study and Future Work
The hail study is best applied as a tool to increase confidence when used with other warning strategies
Values are only reliable for hail, not wind
2010 Convective Season wasn’t quite as active as previous few years, but ALY hail research was still applied during the season
ALY warning forecasters had a severe thunderstorm warning out for every hail report of 1.00” or greater in 2010 (POD = 1.00)
22 reports of hail 1.00” or greater in 2010 (43 total hail reports 0.75” or greater)
The advent of Dual-Pol radar products will have an even greater impact on warning for severe hail
However, this won’t be implemented in the ALY CWA until April 2012
An ER Tech Attachment or similar paper will be written in regarding this study
A new “VIL of the Day” Program may be created for the ALY CWA in the near future using 1.00” criteria

26. Additional Conclusions
ALY Hail Study is most applicable during warm season severe weather events with a freezing level between kft
Warning threshold values may be too high during low freezing level events or too low during very warm air masses
Data has shown supercell thunderstorms produce both severe hail and wind more often as compared to pulse or multi-cellular events
Although 21 July case showed that not every supercell will produce severe hail in our area!

27. Any questions or comments?