Transcript Issues with Transitioning to a New Severe Hail Criteria Presented by: Matt Steinbugl Contributions from: Rich Grumm and John LaCorte NOAA/NWS State College, PA Northeast Regional Operational.

Issues with Transitioning to
a New Severe Hail Criteria
Presented by: Matt Steinbugl
Contributions from:
Rich Grumm and
John LaCorte
NOAA/NWS State College, PA
Northeast Regional Operational Workshop
NROW XI Albany, NY
November 4-5, 2009
We will look at…
• Background
– 1” hail - Why and What ??
• Impacts and Implications
– FAR vs. Low frequency
– Focus on winds
– Implementation/Outreach
• Climatology
– ER, US, PA
• Moving ->> Forward
– Training Focus
– 1” Hail detection techniques
– Dual-Polarization
– Favorable environments
• Summary
Background
• Current Criteria = ¾” (penny) ; New Criteria = 1” (quarter)
– Implementation - January 2010 (Eastern and Southern Region)
– CR started in April and WR followed in June 2009
• Impetus for change:
– Better representation of hail size that produces damage
• Recent engineering study validates the increase in hail size
threshold (Marshall et al.)
– Reduce user complacency to numerous severe thunderstorm
warnings
• This should add more credibility to the end user
• Surveys were mixed but research and climatology support the
criteria change
– From a service improvement/operations perspective,
implementation may be easier than previously anticipated
– From a verification perspective, impact likely on FAR (at least
initially) but perhaps not as much as one might think
Implications and Impacts
• Regional performance – increased FAR
– ER analysis based on last two years of verification suggests
potential FAR increase by as much as 30%
– 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 both)
• Oct 2006 - Sept 2009 ER SVR hail distribution suggests the
frequency of 1” or greater hail is relatively low (less than 50%
and about 35% on average)
– Becoming aware of regional/local hail climatology might make
our jobs easier !
• Severe wind detection techniques now at the forefront of
severe weather warning decision making
– Several calibrated 1” hail techniques to leverage (via CR)
– Training efforts will need to focus on wind signatures as Tstorm
wind gusts now become the driving factor when issuing SVRs
From Salem et al.
1” hail in most ER counties occurs less than 1-2 times a year if that !!!
Oct 2006- Sept 2009
ER SVR Hail by WFO
Severe Hail by WFO
800
0.60
700
0.50
400
0.30
300
0.20
200
0.10
100
WFO
The average frequency (%) of hail >= 1” is about 36%
of all SVR hail reports (black line) in the last 3 years
RNK
RLX
RAH
PHI
PBZ
OKX
MHX
LWX
ILN
ILM
GYX
GSP
CTP
CLE
CHS
CAR
CAE
BUF
BTV
BOX
BGM
0.00
ALY
0
Percentage >= 1"
0.40
500
AKQ
Total # of Events
600
Hail 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
Moving Forward ->>
• Short term (Now until Dual-Polarization)
– Realize and understand the low frequency of 1” hail occurrence
and use this to refine warning decision making/philosophy
– Engage in external outreach to educate and ensure a smooth
transition for our customers
• Better understanding of wind events (MARCs, etc)
– Suspect about 50% of verified storms were by wind alone
– Few measured verification winds, mostly estimated based on
damage
• What really constitutes a damaging wind?
• Leverage (1”) hail detection techniques
– Need to adjust to fit environments (Eastern U.S. vs. the Plains)
– Identify favorable environments
• Mid Level Lapse Rate Anomalies, >= 6.0C/km good indicator
Dual-Pol
• Medium term (Duel-Polarization Era)
– Dual-pol to provide significant benefits in regards to 1” hail criteria
change
– Polarimetric radars transmit and receive both horizontal and
vertical polarization radio wave pulses. Therefore, they measure
both the horizontal and vertical dimensions of cloud and
precipitation particles. This additional information leads to
improved radar estimation of precipitation type and rate.
– Able to detect hailstones rather than infer their presence based on
current WSR-88D limitations
Summary and Conclusions
• Realize and understand that 1” hail is a low probability event
and use this information to your advantage
• Despite potential (negative) impact in FAR, the increased
criteria should generally be transparent and warning operations
will likely remain “business as usual”
• Main driver for warning issuance now becomes severe winds need to focus our efforts here and perhaps commence an
extensive damage study similar to the ones conducted for hail
to determine new threshold
Summary and Conclusions
• Leverage current hail detection techniques and adjust or “recalibrate” to local environment (rather than attempting to
develop a new criterion)
– There is no silver bullet !
• Develop mid level lapse rate anomalies to identify big hail days
(Some offices already doing this ??)
• Foresee little to no impact on the overall number of warnings
issued (warnings largely driven by wind threat)
• Dual-polarization will provide great benefits in hail detection
(still a few years out)
Future Research
1. Develop better radar techniques to identify storms capable
of producing damaging winds
2. Refine CR detection techniques to fit Eastern U.S.
environments and use big events as case studies
3. Develop a more extensive 1” hail climatology database
4. Collaborate on regional studies
Acknowledgements/References
•
•
•
•
•
•
•
Rich Grumm (CTP)
John LaCorte (CTP)
Rosemary Auld (ER)
Dave Manning (ER)
Dave Radell (ER)
Dave Beachler (CTP)
See me for references (there are several)