Issues with Issues with Transitioning to a New Transitioning to a New

Severe Hail CriteriaSevere Hail Criteria Presented by: Matt SteinbuglPresented by: Matt Steinbugl

Contributions from: Contributions from: Rich Grumm andRich Grumm and

John LaCorteJohn LaCorte

NOAA/NWS State College, PANOAA/NWS State College, PA

Northeast Regional Operational Workshop Northeast Regional Operational Workshop NROW XI Albany, NYNROW XI Albany, NYNovember 4-5, 2009November 4-5, 2009

We will look at…We will look at…• BackgroundBackground

– 1” hail - Why and What ??1” hail - Why and What ??

• Impacts and ImplicationsImpacts and Implications– FAR vs. Low frequencyFAR vs. Low frequency– Focus on windsFocus on winds– Implementation/OutreachImplementation/Outreach

• ClimatologyClimatology– ER, US, PAER, US, PA

• Moving ->> ForwardMoving ->> Forward– Training FocusTraining Focus– 1” Hail detection techniques1” Hail detection techniques– Dual-Polarization Dual-Polarization – Favorable environmentsFavorable environments

• SummarySummary

BackgroundBackground• Current Criteria = ¾” (penny) ; New Criteria = 1” (quarter)Current Criteria = ¾” (penny) ; New Criteria = 1” (quarter)

– Implementation - January 2010 (Eastern and Southern Region)Implementation - January 2010 (Eastern and Southern Region)– CR started in April and WR followed in June 2009CR started in April and WR followed in June 2009

• Impetus for change: Impetus for change: – Better representation of hail size that produces damage Better representation of hail size that produces damage

• Recent engineering study validates the increase in hail size Recent engineering study validates the increase in hail size threshold (Marshall et al.)threshold (Marshall et al.)

– Reduce user complacency to numerous severe thunderstorm Reduce user complacency to numerous severe thunderstorm warningswarnings

• This should add more credibility to the end userThis should add more credibility to the end user

• Surveys were mixed but research and climatology support the Surveys were mixed but research and climatology support the criteria changecriteria change– From a service improvement/operations perspective, From a service improvement/operations perspective,

implementation may be easier than previously anticipatedimplementation may be easier than previously anticipated– From a verification perspective, impact likely on FAR (at least From a verification perspective, impact likely on FAR (at least

initially) but perhaps not as much as one might thinkinitially) but perhaps not as much as one might think

Implications and Impacts Implications and Impacts • Regional performance – increased FARRegional performance – increased FAR

– ER analysis based on last two years of verification suggests potential ER analysis based on last two years of verification suggests potential FAR increase by as much as 30% FAR increase by as much as 30%

– This is most likely an artifact of the verification as penny and nickel This is most likely an artifact of the verification as penny and nickel size hail will no longer verify SVRs (whether issued for wind/hail or size hail will no longer verify SVRs (whether issued for wind/hail or both)both)

• Oct 2006 - Sept 2009 ER SVR hail distribution suggests the Oct 2006 - Sept 2009 ER SVR hail distribution suggests the frequency of 1” or greater hail is relatively frequency of 1” or greater hail is relatively lowlow (less than 50% and (less than 50% and about 35% on average)about 35% on average)– Becoming aware of regional/local hail climatology might make our Becoming aware of regional/local hail climatology might make our

jobs easier !jobs easier !

• Severe wind detection techniques now at the forefront of severe Severe wind detection techniques now at the forefront of severe weather warning decision makingweather warning decision making– Several calibrated 1” hail techniques to leverage (via CR)Several calibrated 1” hail techniques to leverage (via CR)– Training efforts will need to focus on wind signatures as Tstorm wind Training efforts will need to focus on wind signatures as Tstorm wind

gusts now become the driving factor when issuing SVRsgusts now become the driving factor when issuing SVRs

1” hail in most ER counties occurs less than 1-2 times a year if that !!!

From Salem et al.

Oct 2006- Sept 2009 Oct 2006- Sept 2009 ER SVR Hail by WFOER SVR Hail by WFO

The average frequency (%) of hail >= 1” is about 36% The average frequency (%) of hail >= 1” is about 36% of all SVR hail reports (black line) in the last 3 years of all SVR hail reports (black line) in the last 3 years

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Hail ClimatologyHail Climatology PA Hail (1950-2008) ER Oct 06 - Sept 09

Total Reports 2701 8649

Total Reports >= 1” 1190 3047

% of Reports >= 1” 44% 35%

Mean diameter 1” 0.95”

Median diameter 0.88” 0.88”

Largest Hailstone 4.50” 4.25”

Top 3 Events 6/2/98, 6/24/85, 6/16/08

6/16, 5/20, 6/22 , 2008

** Hail data might be biased toward relative sizes** Hail data might be biased toward relative sizes

Moving Forward ->>Moving Forward ->>• Short term (Now until Dual-Polarization)Short term (Now until Dual-Polarization)

– Realize and understand the low frequency of 1” hail occurrence and use Realize and understand the low frequency of 1” hail occurrence and use this to refine warning decision making/philosophythis to refine warning decision making/philosophy

– Engage in external outreach to educate and ensure a smooth transition Engage in external outreach to educate and ensure a smooth transition for our customersfor our customers

• Better understanding of wind events (MARCs, etc)Better understanding of wind events (MARCs, etc)– Suspect about 50% of verified storms were by wind aloneSuspect about 50% of verified storms were by wind alone– Few measured verification winds, mostly estimated based on damageFew measured verification winds, mostly estimated based on damage

• What really constitutes a damaging wind?What really constitutes a damaging wind?

• Leverage (1”) hail detection techniquesLeverage (1”) hail detection techniques– Need to adjust to fit environments (Eastern U.S. vs. the Plains)Need to adjust to fit environments (Eastern U.S. vs. the Plains)– Identify favorable environments Identify favorable environments

• Mid Level Lapse Rate Anomalies, >= 6.0C/km good indicatorMid Level Lapse Rate Anomalies, >= 6.0C/km good indicator

Dual-Pol Dual-Pol

• Medium term (Duel-Polarization Era)Medium term (Duel-Polarization Era)– Dual-pol to provide significant benefits in regards to 1” hail criteria Dual-pol to provide significant benefits in regards to 1” hail criteria

change change

– Polarimetric radars transmit and receive both Polarimetric radars transmit and receive both horizontal and and vertical polarization radio wave pulses. Therefore, they measure both the polarization radio wave pulses. Therefore, they measure both the horizontal and vertical dimensions of cloud and precipitation horizontal and vertical dimensions of cloud and precipitation particles. This additional information leads to improved radar particles. This additional information leads to improved radar estimation of precipitation type and rate.estimation of precipitation type and rate.

– Able to detect hailstones rather than infer their presence based on Able to detect hailstones rather than infer their presence based on current WSR-88D limitations current WSR-88D limitations

Summary and Summary and ConclusionsConclusions

• Realize and understand that 1” hail is a low probability event Realize and understand that 1” hail is a low probability event and use this information to your advantage and use this information to your advantage

• Despite potential (negative) impact in FAR, the increased Despite potential (negative) impact in FAR, the increased criteria should generally be transparent and warning criteria should generally be transparent and warning operations will likely remain “business as usual”operations will likely remain “business as usual”

• Main driver for warning issuance now becomes severe winds - Main driver for warning issuance now becomes severe winds - need to focus our efforts here and perhaps commence an need to focus our efforts here and perhaps commence an extensive damage study similar to the ones conducted for hail extensive damage study similar to the ones conducted for hail to determine new thresholdto determine new threshold

Summary and Summary and ConclusionsConclusions

• Leverage current hail detection techniques and adjust or “re-Leverage current hail detection techniques and adjust or “re-calibrate” to local environment (rather than attempting to calibrate” to local environment (rather than attempting to develop a new criterion)develop a new criterion)– There is no silver bullet !There is no silver bullet !

• Develop mid level lapse rate anomalies to identify big hail days Develop mid level lapse rate anomalies to identify big hail days (Some offices already doing this ??)(Some offices already doing this ??)

• Foresee little to no impact on the overall number of warnings Foresee little to no impact on the overall number of warnings issued (warnings largely driven by wind threat)issued (warnings largely driven by wind threat)

• Dual-polarization will provide great benefits in hail detection Dual-polarization will provide great benefits in hail detection (still a few years out)(still a few years out)

Future ResearchFuture Research

1.1. Develop better radar techniques to identify storms capable Develop better radar techniques to identify storms capable of producing damaging windsof producing damaging winds

2.2. Refine CR detection techniques to fit Eastern U.S. Refine CR detection techniques to fit Eastern U.S. environments and use big events as case studies environments and use big events as case studies

3.3. Develop a more extensive 1” hail climatology databaseDevelop a more extensive 1” hail climatology database

4. Collaborate on regional studies4. Collaborate on regional studies

Acknowledgements/Acknowledgements/ReferencesReferences

• Rich Grumm (CTP)Rich Grumm (CTP)

• John LaCorte (CTP)John LaCorte (CTP)

• Rosemary Auld (ER)Rosemary Auld (ER)

• Dave Manning (ER)Dave Manning (ER)

• Dave Radell (ER)Dave Radell (ER)

• Dave Beachler (CTP)Dave Beachler (CTP)

• See me for references (there are several)See me for references (there are several)