Improving Forecasts for High Impact Improving Forecasts for High Impact Sub-Advisory Snow SquallsSub-Advisory Snow Squalls

David Nicosia, WCM, David Nicosia, WCM,

NOAA/National Weather Service, Binghamton, NYNOAA/National Weather Service, Binghamton, NY

Greg Devoir, Senior Forecaster, Greg Devoir, Senior Forecaster,

NOAA/National Weather Service, State College, PANOAA/National Weather Service, State College, PA

Richard Grumm, SOO, Richard Grumm, SOO,

NOAA/National Weather Service, State College, PANOAA/National Weather Service, State College, PA

James Dickey, SCEP, James Dickey, SCEP,

NOAA/National Weather Service, State College, PANOAA/National Weather Service, State College, PA

Introduction• The Problem

• Look at two deadly snow squall episodes in Pennsylvania.

– Examine the synoptic and meso-scale environments that supported these deadly squalls.

– Look at radar evolution.

• Previous Research.

• Implications for Forecasting Snow Squalls.

– Anticipating squall formation in advance by model data.

– Real-time Detection.

– Anticipating road conditions.

– Dissemination issues.

• Conclusions and Future Research

DeVoir (2004)

The Problem

Snow Squalls: Winter’s Underrated Killer• Snow squalls present a grave danger to motorists.

• In Pennsylvania, snow squalls kill more people than larger scale winter storms!

– Exceeds lightning, and tornadoes.

– Close third to flooding and thunderstorm winds.

– In a couple years, it was the number 1 killer.

Pennsylvania HighwaysPennsylvania Highways• 44thth highest interstate mileage in the United States. highest interstate mileage in the United States.

• 11stst in the eastern U.S. in the eastern U.S.

• Major travel and transport arteries from New York Major travel and transport arteries from New York City, Philadelphia and New England. City, Philadelphia and New England.

January 6, 2004: January 6, 2004: I-80 Milesburg, PAI-80 Milesburg, PA

Centre Daily Times (CDT) Michelle Klein

CDT Niki Desautels

AP Photo

CDT Niki Desautels

• 6 dead 6 dead

• 17 injured17 injured

• 20 Tractor Trailers and 17 20 Tractor Trailers and 17 Automobiles involvedAutomobiles involved

Radar evolution

Water Vapor Imagery and 300 mb Height(dam) and Tropopause Pressure (mb)

IR Imagery and 700 mb height(dam) and temperature (C)

Thermal Advection(C/12hr) and Potential Temp (K) Cross Section

Low-level destabilizationwhere snow squall formed

925 mb to 700 mb Lapse Rates (C/km)

BUFKIT Sounding Data

February 10, 2008February 10, 2008

• Hazleton, PA: I-81Hazleton, PA: I-81

– 68-vehicle pileup 68-vehicle pileup

– 1 dead, dozens injured1 dead, dozens injured

– Snow squall with arctic Snow squall with arctic front. front.

Radar evolution

Water Vapor Imagery and 300 mb Height(dam) and Tropopause Pressure (mb)

IR Imagery and 700 mb height(dam) and temperature (C)

Thermal Advection(C/12hr) and Potential Temp (K) Cross Section

Low-level destabilizationwhere snow squall formed

925 mb to 700 mb Lapse Rates (C/km)

Analogous To Summer Time Convection

• CAPE present, steep low-level lapse rates.

• Lifting mechanism.

• Forecasters can anticipate the development of wintertime convection from model data 1-2 days in advance.

• Radar detection- timing and arrival over the next 1-2 hours.

Previous Research on Winter Convection

• Lundstedt (1993)

– Steep low-level lapse rates as inferred in the NGM FOUS data. T1 minus T5 of 10 C or greater

– Boundary layer moisture (R1) > 50%

– Lifting Mechanism present. LI increases by 8 C in 12 hours indicative of a boundary.

• Pettegrew et al. 2009 documented a line of severe thunderstorms with winds greater than 50 knots, lightning and heavy snow.

– Cape present, lapse rate almost dry adiabatic to 625 mb

– Strong front as lifting mechanism.

– Wind shear present.

Other factors Important for Forecasting the Impact of Snow Squalls

• NWS is focusing on forecasting high impact events.

• Societal factors

– Travel patterns (holidays, rush hour etc.), first snow of the season.

• Road Conditions

– Mild conditions prior to cold front led to wet roads which subsequently froze and became snow covered with snow squall arrival.

– Spotter reports.

– DOT road sensor data.

– Web cams.

Road Sensor DataRoad Sensor Data

Web Cams Web Cams

Getting the Word Out: A Challenge

• High Impact Snow Squalls do not meet National Weather Service Winter Weather or Lake Effect Snow Advisory Criteria.

Dissemination Solutions

• NWS State College partnership with PENNDOT for notification on I-80 has worked.

• NWS Binghamton issues special weather statements with timing, snow squall location and highlight dangers using WarnGen.

• Need timely alerting for the public, EMs and DOTs.

– A separate short fused warning to address this hazard? Snow squall warning?

– Winter Storm Warning or Winter Weather Advisory?

• Use of “SPS” EAS/SAME code is being considered by NWS Binghamton to broaden dissemination of alerts in the meantime.

PAZ012-018-019-045-049-230045-NORTHERN CENTRE-NORTHERN CLINTON-SOUTHERN CENTRE-SOUTHERN CLINTON-UNION-749 PM EDT FRI JAN 22 2006

...A SNOW SQUALL WILL AFFECT UNION...CENTRE AND CLINTON COUNTIES...

AT 748 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SNOW SQUALL 12 MILES NORTH OF BELLEFONTE...MOVING EAST AT 30 MPH. THE SQUALL WILL BE NEAR BALD EAGLE STATE PARK...HOWARD AROUND 755 PM...BEECH CREEK AROUND 800 PM...LAMAR...MILL HALL...LOCK HAVEN AROUND 810 PM...MACKEYVILLE...REBERSBURG AROUND 815 PM...LOGANTON AROUND 830 PM AND CARROLL AROUND 835 PM.

THIS WILL IMPACT THE FOLLOWING CENTRAL PENNSYLVANIA INTERSTATES...I-80 BETWEEN MILE MARKERS 165 AND 199.

THIS WILL ALSO IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 220...STATE ROAD 45.

THIS WILL IMPACT THE FOLLOWING CENTRAL PENNSYLVANIA INTERSTATES...I-80 BETWEEN MILE MARKERS 165 AND 199.

THIS WILL ALSO IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 220...STATE ROAD 45.

THE SNOW WILL RAPIDLY DROP VISIBILITIES IN THE SQUALL TO NEAR ZERO. USE EXTREME CAUTION IF YOU MUST TRAVEL INTO OR THROUGH THIS POTENTIALLY DANGEROUS SNOW SQUALL. CONSIDER DELAYING TRAVEL UNTIL THE SQUALL PASSES YOUR LOCATION.

$$

THE SNOW WILL RAPIDLY DROP VISIBILITIES IN THE SQUALL TO NEAR ZERO. USE EXTREME CAUTION IF YOU MUST TRAVEL INTO OR THROUGH THIS POTENTIALLY DANGEROUS SNOW SQUALL. CONSIDER DELAYING TRAVEL UNTIL THE SQUALL PASSES YOUR LOCATION.

$$

Preliminary Results and Future Research

• Need to examine more cases.

• Convective signatures in model data 1-2 days in advance.

– Any CAPE present.

– Destabilization from approaching short wave.

– Low-level lapse rates > 8 C/km

– Arctic front as lifting mechanism.

• Radar detection- 1 to 2 hours in advance.

• Road sensor data and societal factors to determine the potential impact of event.

What can forecasters do? What can forecasters do?

• Mention potential in hazardous weather outlook.

• For the high impact events:

o Notify emergency management

o DOTs

o Conference calls?

• Issue special weather statements with timing, locations, interstate mile markers of impending snow squalls.

• Partnerships with DOTs, emergency management for notification.

• Use of EAS or triggering SAME feature on NOAA weather radios is worth exploring.

References References

DeVoir, G. A., 2004: High impact sub-advisory snow events: the need to effectively communicate the threat of short duration high intensity snowfall. 20th Conference on Weather Analysis and Forecasting, Seattle, WA.

Lundstedt, W.,1993: A method to forecast wintertime instability and non-lake effect snow squalls across northern New England NWS Eastern Region Technical Attachment No.93-11A.

Pettegrew, B.P.; Market, P.S; Wolf, R.A; Holle, R.L; Demetriades 2009: A Case Study of Severe Winter Convection in the Midwest. Wea. and Forecasting. 24 (1) 121-139