1. Matthew Steinbugl – NOAA/NWS/CTP 9 th Northeast Regional Operational Workshop (NROW) November 7-8, 2007 17 August 2007 Severe Weather Episode: Fingerprints of a Northwest- Flow Event

2. NROW November 7-8, 2007 Overview Briefly Compare/Contrast Synoptic Patterns and some Meteorological Parameters associated with NWF events Examine Large Scale Forcing/Jet Dynamics Thermodynamic environment/Mesoscale boundaries Early Forecasts/Event Evolution Display Model Data/Radar Imagery Potential Near-Miss for 2007 LLWS…WHAT IFs

3. NROW November 7-8, 2007 NWF Synoptic Climatology Highlights (Johns 1984) SW flow (SWF) vs. NW flow (NWF) – seasonal frequencies, jet streams, baroclinicity NWF events usually characterized by strong thermodynamic forcing in vicinity of surface boundaries Mid/Upper jet typically plays an indirect role in determining outbreak location Influence of the 500mb short wave trough generally weak Differences from the basic (composite) pattern occur frequently Large directional and small speed contributions to the wind shear vector

4. NROW November 7-8, 2007 17 August 2007 Event Highlights Not a classic NWF case (digging short wave, anomalous cyclonically curved upper jet, location vs. composite) Primary foci for vigorous ascent and rapid convective development included coupled upper level jet streaks superimposed within region of maximum PVA (divergence) aloft Relatively “Early” event time (16-18Z) versus severe weather climatology Similar to NWF synoptic set-up in that outbreak occurred – In the convergence zone near a sfc low center and attendant warm front. –South of the 500mb jet (anticyclonic-shear side). –Other similarities noted as well.

5. NROW November 7-8, 2007 17 August 2007 Event Overview 38/216 reports from PA Occurred between 12-3pm Nickel to baseball size hail Rotating supercells with TVSs Wind damage but no tornadoes

6. NROW November 7-8, 2007 500hPa event location comparison

7. NROW November 7-8, 2007 Anomalous 500 hPa trough and upper jet 250 hPa u and v winds500 hPa heights

8. NROW November 7-8, 2007 Coupled jets and corresponding UVM Primary mechanism for rapid intensification of convection by enhancing 700-500mb UVVELs RUC 300mb isotachs (fill) ageostrophic wind and 700-500mb omega valid at 1700/1900 UTC. UVM increases from -6 to -12 microbars/sec.

9. NROW November 7-8, 2007 Jet Streak Analysis/Vertical Circulations

10. NROW November 7-8, 2007 - Vorticity Advection – An approximation of divergence aloft X PVA (divergence) superimposed within coupled jet circulation induced significant large scale ascent This was associated with the explosive convection over Central PA

11. NROW November 7-8, 2007 Evolution of Surface/mesoscale boundaries and the release of conditional instability 12Z 18Z 15Z 00Z

12. NROW November 7-8, 2007 Early Forecasts Initial slight risk/general thunder areas where south and east of where severe convection developed. Forecast was amended around 1245 pm. Local and Regional WFO forecasts did not indicate the potential for thunderstorms. A collaboration issue serving as the primary motivation for this case study.

13. NROW November 7-8, 2007 SVR Tstorm Watch – 135pm

14. NROW November 7-8, 2007 Certainly not Cut and Dry… MSLP 15ZMSLP 18ZPWAT 18Z

15. NROW November 7-8, 2007 1700 UTC IPT LAPS Sounding TT = 50 FzgLvl= 11.8 Stm Motion = 294/25kts 0-3km SRH = 223 m2s2 LI = -6.1 CAPE = 1700 J/kg CIN = 0 J/kg 70-80KT midlvl speed max Lolvl wnd backed

16. NROW November 7-8, 2007 High resolution NAM did very well SB CAPE Conv Pcpn LI Showalter SB CAPEConv Pcpn LI Showalter 15Z21Z

17. NROW November 7-8, 2007 SREF 6hr Prob of 0.05” and IPT CAPE Plume 18 to 00z Mean ~500 Jkg -1 A few members over 1000 Jkg -1

18. NROW November 7-8, 2007 Water Vapor/300mb isotachs Loop 1515-1630Z loop Convection develops over Central PA in coupled jet “X” denotes S/W crossing Lake Erie providing additional large scale lift/PVA Little to no moisture in the mid to upper levels X

19. NROW November 7-8, 2007 Radar Loop 1528-1726Z Rapid initiation, intensification IPT storm splits, right mover becomes storm of interest SVR issued 1610Z TOR issued 1656Z First Hail report approx 1700Z IPT

20. NROW November 7-8, 2007 Loop continued 1730-1820Z Radar Loop continued 1730-1820Z Storm continues ESE (rightmover) Several large hail reports Wind damage No reports of tornadoes Lancaster county storm was also severe (hail/damaging winds)

21. NROW November 7-8, 2007 0.5° Reflectivity/SRM Close-up 1652Z 70+ dBZ TVS IPT

22. NROW November 7-8, 2007 0.5° Reflectivity/SRM Close-up 1704Z… 12 minutes later 70+ dBZTVS

23. NROW November 7-8, 2007 4-Panel View 1.3°, 2.4°, 3.1°, 4.0° Four panel display –1.3 = 73dBZ, 12kft –2.4 = 72dBZ, 19kft –3.1 = 69dBZ, 24kft –4.0 = 66dBZ, 30kft Height of: 0°C = 12kft, -20°C= 22kft -60-70dBZ depth of 30kft - Deep Well-defined, persistent mesocyclone (not shown) -Lost Archive Level II data feed ( NO GR2)

24. NROW November 7-8, 2007 Storm Photos/Damage Williamson

25. NROW November 7-8, 2007 Summary and Conclusions NWF event awareness – watch out! Sometimes difficult to forecast – large forcing, subtle features, rapid evolution = need high situational awareness Coupled jet circulation juxtaposed in max PVA/divergence collocated in moist/unstable warm sector = vigorous UVM Favorable shear profiles INVOF sfc warm front = supercell environment Unique NWF event - but many similarities or “fingerprints” to synoptic climatology/parameters Near-miss worst case scenario for the 2007 LLWS

26. NROW November 7-8, 2007 2007 LLWS WHAT Ifs! Pre-Event Awareness Low (SPC Convective Outlook/CTP HWO) – “Sudden” Had a tornado struck the stadium (capacity of around 9,000 with room for an additional 30- 35,000 on the terraced hills beyond the outfield Storm hit just prior to the first pitch of the 2007 LLWS – time for evacuations? Where? Shelter for approx. 40K +? Attendees could have been subjected to large hail/damaging winds – numerous injuries/possible fatalities? Lightning safety – considering the venue

27. NROW November 7-8, 2007 Questions Questions Matthew.Steinbugl@noaa.gov http://nws.met.psu.edu/severe/2007/17Aug2007.pdf