17 August 2007 Severe Weather Episode: Fingerprints of a Northwest-Flow Event

Matthew Steinbugl – NOAA/NWS/CTPMatthew Steinbugl – NOAA/NWS/CTP99thth Northeast Regional Operational Northeast Regional Operational

Workshop (NROW)Workshop (NROW)November 7-8, 2007November 7-8, 2007

17 August 2007 Severe Weather 17 August 2007 Severe Weather Episode: Fingerprints of a Episode: Fingerprints of a

Northwest-Flow Event Northwest-Flow Event

NROW November 7-8, 2007NROW November 7-8, 2007

OverviewOverview

Briefly Compare/Contrast Synoptic Patterns Briefly Compare/Contrast Synoptic Patterns and some Meteorological Parameters and some Meteorological Parameters associated with NWF eventsassociated with NWF events

Examine Large Scale Forcing/Jet DynamicsExamine Large Scale Forcing/Jet Dynamics

Thermodynamic environment/Mesoscale Thermodynamic environment/Mesoscale boundariesboundaries

Early Forecasts/Event EvolutionEarly Forecasts/Event Evolution

Display Model Data/Radar Imagery Display Model Data/Radar Imagery

Potential Near-Miss for 2007 LLWS…WHAT Potential Near-Miss for 2007 LLWS…WHAT IFsIFs


NWF Synoptic Climatology Highlights NWF Synoptic Climatology Highlights

(Johns 1984)(Johns 1984) SW flow (SWF) vs. NW flow (NWF) – seasonal SW flow (SWF) vs. NW flow (NWF) – seasonal frequencies, jet streams, baroclinicityfrequencies, jet streams, baroclinicityNWF events usually characterized by strong NWF events usually characterized by strong thermodynamic forcing in vicinity of surface thermodynamic forcing in vicinity of surface boundariesboundariesMid/Upper jet typically plays an indirect role in Mid/Upper jet typically plays an indirect role in determining outbreak locationdetermining outbreak locationInfluence of the 500mb short wave trough Influence of the 500mb short wave trough generally weakgenerally weakDifferences from the basic (composite) pattern Differences from the basic (composite) pattern occur frequentlyoccur frequentlyLarge directional and small speed contributions to Large directional and small speed contributions to the wind shear vectorthe wind shear vector


17 August 2007 Event Highlights17 August 2007 Event Highlights

Not a classic NWF case (digging short wave, Not a classic NWF case (digging short wave, anomalous cyclonically curved upper jet, location vs. anomalous cyclonically curved upper jet, location vs. composite)composite)Primary foci for vigorous ascent and rapid convective Primary foci for vigorous ascent and rapid convective development included coupled upper level jet streaks development included coupled upper level jet streaks superimposed within region of maximum PVA superimposed within region of maximum PVA (divergence) aloft(divergence) aloftRelatively “Early” event time (16-18Z) versus severe Relatively “Early” event time (16-18Z) versus severe weather climatology weather climatology Similar to NWF synoptic set-up in that outbreak Similar to NWF synoptic set-up in that outbreak occurredoccurred– In the convergence zone near a sfc low center and In the convergence zone near a sfc low center and

attendant warm front. attendant warm front. – South of the 500mb jet (anticyclonic-shear side). South of the 500mb jet (anticyclonic-shear side). – Other similarities noted as well.Other similarities noted as well.


17 17 AugustAugust 2007 Event Overview 2007 Event Overview

38/216 reports from PA38/216 reports from PA

Occurred between 12-3pmOccurred between 12-3pm

Nickel to baseball size hailNickel to baseball size hail

Rotating supercells with Rotating supercells with TVSsTVSs

Wind damage but no Wind damage but no tornadoestornadoes


500hPa event location comparison500hPa event location comparison


Anomalous 500 hPa trough and Anomalous 500 hPa trough and upper jetupper jet

250 hPa u and v winds500 hPa heights


Coupled jets and corresponding UVM

Primary Primary mechanism mechanism for rapid for rapid intensificatiointensification of n of convection by convection by enhancing enhancing 700-500mb 700-500mb UVVELsUVVELs

RUC 300mb isotachs (fill) ageostrophic wind and 700-500mb omega valid at 1700/1900 UTC. UVM increases from -6 to -12 microbars/sec.


Jet Streak Analysis/Vertical Jet Streak Analysis/Vertical CirculationsCirculations


- Vorticity Advection – An approximation of divergence aloft

X

PVA (divergence) PVA (divergence) superimposed superimposed within coupled jet within coupled jet circulation circulation induced induced significant large significant large scale ascentscale ascentThis was This was associated with associated with the explosive the explosive convection over convection over Central PACentral PA


Evolution of Surface/mesoscale Evolution of Surface/mesoscale boundaries and the release of conditional boundaries and the release of conditional

instabilityinstability

12Z

18Z

15Z

00Z


Early ForecastsEarly Forecasts

Initial slight risk/general thunder areas where south and east Initial slight risk/general thunder areas where south and east of where severe convection developed. Forecast was of where severe convection developed. Forecast was amended around 1245 pm.amended around 1245 pm.Local and Regional WFO forecasts did not indicate the Local and Regional WFO forecasts did not indicate the potential for thunderstorms. A collaboration issue serving as potential for thunderstorms. A collaboration issue serving as the primary motivation for this case study. the primary motivation for this case study.


SVR Tstorm Watch – 135pmSVR Tstorm Watch – 135pm


Certainly not Cut and Dry…Certainly not Cut and Dry…

MSLP 15Z MSLP 18Z PWAT 18Z


1700 UTC IPT LAPS Sounding1700 UTC IPT LAPS Sounding

TT = 50TT = 50FzgLvl= 11.8FzgLvl= 11.8Stm Motion = Stm Motion = 294/25kts294/25kts0-3km SRH = 223 0-3km SRH = 223 m2s2m2s2LI = -6.1LI = -6.1CAPE = 1700 J/kgCAPE = 1700 J/kgCIN = 0 J/kgCIN = 0 J/kg70-80KT midlvl 70-80KT midlvl speed maxspeed maxLolvl wnd backedLolvl wnd backed


High resolution NAM did very wellHigh resolution NAM did very well

SB CAPE Conv Pcpn

LI Showalter

SB CAPE Conv Pcpn

LI Showalter

15Z 21Z


SREF 6hr Prob of 0.05” and IPT CAPE SREF 6hr Prob of 0.05” and IPT CAPE PlumePlume

18 to 00z

Mean ~500 Jkg-1

A few members over 1000 Jkg-1


Water Vapor/300mb isotachs Loop

1515-1630Z loop1515-1630Z loop

Convection Convection develops over develops over Central PA in Central PA in coupled jetcoupled jet

““X” denotes S/W X” denotes S/W crossing Lake Erie crossing Lake Erie providing providing additional large additional large scale lift/PVAscale lift/PVA

Little to no Little to no moisture in the moisture in the mid to upper mid to upper levelslevels

X


Radar Loop 1528-1726ZRadar Loop 1528-1726Z

Rapid Rapid initiation, initiation, intensificationintensification

IPT storm IPT storm splits, right splits, right mover mover becomes storm becomes storm of interestof interest

SVR issued SVR issued 1610Z1610Z

TOR issued TOR issued 1656Z1656Z

First Hail report First Hail report approx 1700Zapprox 1700Z

IPT


Radar Loop continued 1730-1820Z Loop continued 1730-1820Z

Storm Storm continues ESE continues ESE (rightmover)(rightmover)

Several large Several large hail reportshail reports

Wind damageWind damage

No reports of No reports of tornadoestornadoes

Lancaster Lancaster county storm county storm was also severe was also severe (hail/damaging (hail/damaging winds)winds)


0.50.5° Reflectivity/SRM Close-up° Reflectivity/SRM Close-up 1652Z1652Z

70+ dBZ TVSIPT


0.5° Reflectivity/SRM Close-up 1704Z…

12 minutes later

70+ dBZ TVS


4-Panel View 1.3°, 2.4°, 3.1°, 4.0°4-Panel View 1.3°, 2.4°, 3.1°, 4.0°

Four panel displayFour panel display– 1.3 = 73dBZ, 12kft1.3 = 73dBZ, 12kft– 2.4 = 72dBZ, 19kft2.4 = 72dBZ, 19kft– 3.1 = 69dBZ, 24kft3.1 = 69dBZ, 24kft– 4.0 = 66dBZ, 4.0 = 66dBZ, 30kft30kft

Height of:Height of:

0°C = 12kft, -20°C= 0°C = 12kft, -20°C= 22kft22kft

-60-70dBZ depth of -60-70dBZ depth of

30kft30kft

- Deep Well-defined, - Deep Well-defined, persistent persistent mesocyclone (not mesocyclone (not shown)shown)

- Lost Archive Level Lost Archive Level II data feed ( NO II data feed ( NO GR2)GR2)


Storm Photos/DamageStorm Photos/Damage

Williamson


Summary and ConclusionsSummary and Conclusions

NWF event awareness – watch out!NWF event awareness – watch out!

Sometimes difficult to forecast – large forcing, subtle Sometimes difficult to forecast – large forcing, subtle features, rapid evolution = need high situational features, rapid evolution = need high situational awarenessawareness

Coupled jet circulation juxtaposed in max Coupled jet circulation juxtaposed in max PVA/divergence collocated in moist/unstable warm PVA/divergence collocated in moist/unstable warm sector = vigorous UVMsector = vigorous UVM

Favorable shear profiles INVOF sfc warm front = Favorable shear profiles INVOF sfc warm front = supercell environmentsupercell environment

Unique NWF event - but many similarities or Unique NWF event - but many similarities or “fingerprints” to synoptic climatology/parameters“fingerprints” to synoptic climatology/parameters

Near-miss worst case scenario for the 2007 LLWSNear-miss worst case scenario for the 2007 LLWS


2007 LLWS WHAT Ifs!2007 LLWS WHAT Ifs!

Pre-Event Awareness Low (SPC Convective Pre-Event Awareness Low (SPC Convective Outlook/CTP HWO) – “Sudden”Outlook/CTP HWO) – “Sudden”Had a tornado struck the stadium (capacity Had a tornado struck the stadium (capacity of around 9,000 with room for an additional of around 9,000 with room for an additional 30-35,000 on the terraced hills beyond the 30-35,000 on the terraced hills beyond the outfieldoutfieldStorm hit just prior to the first pitch of the Storm hit just prior to the first pitch of the 2007 LLWS – time for evacuations? Where? 2007 LLWS – time for evacuations? Where? Shelter for approx. 40K +?Shelter for approx. 40K +?Attendees could have been subjected to Attendees could have been subjected to large hail/damaging winds – numerous large hail/damaging winds – numerous injuries/possible fatalities?injuries/possible fatalities?Lightning safety – considering the venueLightning safety – considering the venue


QuestionsQuestions

[email protected]@noaa.govgov

http://nws.met.psu.edu/severe/http://nws.met.psu.edu/severe/2007/17Aug2007.pdf2007/17Aug2007.pdf

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17 August 2007 Severe Weather Episode: Fingerprints of a Northwest-Flow Event