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

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 2009 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

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 2010-2011 Albany (ALY) SCEP Student Rihaan Gangat has been helping with the data analysis and data entry 2009-2010 ALY STEP Student Rebecca Darrow helped evaluate some of the preliminary statistical data

Data Used in the Study Examined hail reports from minor and major events from 2005-2010 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. 2010 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 2004-2005 have limited radar data, so assessing each parameter has been difficult for some of the reports

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

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

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

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

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

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

Severe vs. Non-Severe Hail 0.25-0.88” (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

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

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

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

Litchfield, CT Supercell Storm Reports First produced severe hail around 1905- 1910 UTC Additional severe hail 1944-1951 UTC Wind damage 1905- 1926 and 1950-2005 UTC Tornado from 1951- 2005 UTC in ALY area

FSI-4D Storm Investigator at 1902 UTC Volume scan just prior to first report of hail 50 dBZ reach above 31.0 kft 65 dBZ reach well above 18.7 kft CAPPI set to -20° Celsius level

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

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

KENX Cross Section at 1943 UTC 50 dBZ (red color) still well exceeding 31.0 kft 65 dBZ (dark pink color) as high as 23.0 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

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

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

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

Storm Reports from Berkshire County Storm only produced pea to half-inch size hail in Berkshire County One tree reported down at 1830 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 1.25 inches) in central Mass.

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 2011 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

Additional Conclusions ALY Hail Study is most applicable during warm season severe weather events with a freezing level between 10.0-12.0 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!

Any questions or comments? Brian.Frugis@noaa.gov Tom.Wasula@noaa.gov