SWODY1
SPC AC 221615
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1115 AM CDT TUE JUN 22 2010
VALID 221630Z - 231200Z
...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF
NEB...SD...IA...SRN MN...SW WI...AND NRN IL...
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK
AREA...FROM THE CNTRL HI PLNS TO THE OH VLY AND MID ATLANTIC
STATES/NORTHEAST...
...SYNOPSIS...
SEVERAL UPPER S/WV TROUGHS/ENHANCED BY OVERNIGHT MCS ACTIVITY ARE
TRACKING ACROSS THE TOP OF SRN PLAINS RIDGE AS THE MAIN TROUGH OVER
THE WRN U.S. LIFTS NEWD INTO THE HIGH PLAINS BY LATER TONIGHT.
INTENSIFYING MID/UPPER WIND MAX WILL ACCOMPANY THE WRN TROUGH ACROSS
THE CENTRAL ROCKIES INTO THE PLAINS OVERNIGHT.
RESERVOIR OF VERY WARM/MOIST AND UNSTABLE AIR REMAINS AVAILABLE
ACROSS MUCH OF THE SRN CONUS E OF ROCKIES FOR FUEL OF THE CONTINUED
SERIES OF MCS/S THAT HAVE BEEN HAVE BEEN AFFECTING THE NRN U.S. FROM
THE ROCKIES TO THE OH VALLEY FOR SEVERAL DAYS.
...UPPER OH VALLEY TO THE MID ATLANTIC...
SHORTWAVE TROUGH...CURRENTLY TRACKING EWD INTO THE LOWER GREAT
LAKES/UPPER OH VALLEY PER WATER VAPOR IMAGERY...WILL MOVE EWD INTO
NY/PA AND NRN VA/MD THIS AFTERNOON. 12Z UPPER AIR DATA INDICATED 40
KT WLY MIDLEVEL FLOW WITHIN THE BASE OF THIS TROUGH OVER OH.
OBJECTIVE ANALYSIS SHOWED EFFECTIVE BULK SHEAR ALREADY INCREASING
ACROSS CENTRAL PA TO NRN VA AS THE STRONGER FLOW ALOFT SPREADS EWD.
IN THE LOW LEVELS...SURFACE FRONT ATTENDANT TO THE SHORTWAVE TROUGH
EXTENDED SSWWD FROM SWRN ONTARIO THROUGH CENTRAL OH. THIS BOUNDARY
WILL CONTINUE EWD TODAY AND MARK THE WRN EXTENT OF THE SEVERE
WEATHER THREAT.
CLOUDINESS/FILTERED SUNSHINE ACROSS PA...ASSOCIATED WITH CIRRUS AND
LEADING BAND OF ONGOING CONVECTION OVER CENTRAL PA TO THE ERN WV
PANHANDLE IS LIMITING SURFACE HEATING SOME THIS MORNING. THIS
COMBINED WITH WEAK MIDLEVEL LAPSE RATES APPEARS TO BE RESULTING IN A
SLOWER DESTABILIZATION OF THE AIR MASS THUS FAR. HOWEVER... FURTHER
DIABATIC HEATING WITHIN A MOIST AIR MASS IS EXPECTED TO SUPPORT AT
LEAST MODERATE INSTABILITY BY THIS AFTERNOON WITH MLCAPE 1000-1500
J/KG EXTENDING FROM OH INTO CENTRAL PA AND SWD TO VA/MD.
12Z WRF-HRRR SUGGESTED THE ONGOING STORMS OVER CENTRAL PA TO ERN WV
PANHANDLE WILL CONTINUE TO WEAKEN...WITH NEW TSTMS DEVELOPING OVER
WRN PA TO WV AROUND 17Z AS THE FRONT MOVES EWD. MODERATE
INSTABILITY AND EFFECTIVE BULK SHEAR UP TO 40 KT WILL SUPPORT
ORGANIZED STORMS WITH A THREAT OF HAIL...STRONG WIND GUSTS AND A
POTENTIAL TORNADO THREAT. THE TORNADO THREAT WILL BE GREATER IN ANY
LOCATION WHERE LOW LEVEL WINDS ARE MORE SLY...HENCE INCREASING LOW
LEVEL DIRECTIONAL SHEAR. GREATEST TORNADO THREAT SHOULD BE EAST OF
THE MOUNTAINS. HOWEVER...FORECAST SOUNDINGS SUGGEST SURFACE WINDS
AHEAD OF THE FRONT IN WRN PA WILL REMAIN FAVORABLY BACKED TO SUPPORT
A TORNADO THREAT WITH INITIAL ACTIVITY PRIOR TO WINDS VEERING WITH
FRONTAL PASSAGE.
...CENTRAL HIGH PLAINS TO MID/UPPER MS VALLEY...
STRONG DAYTIME HEATING SHOULD RELOAD THE INSTABILITY ACROSS MUCH OF
THE CENTRAL PLAINS NEWD INTO MID/UPPER MS VALLEY AHEAD OF THE WEAK
COLD FRONT FROM THE CENTRAL DAKOTAS SWWD TO THE CENTRAL ROCKIES.
GIVEN 40-50 KT DEEP SW TO WLY SHEAR ACROSS THE ENTIRE REGION... AND
SBCAPE RANGING FROM AOA 2500 J/KG IN THE HI PLNS TO ABOVE 4000 J/KG
IN THE MS VLY...SUSTAINED SUPERCELLS APPEAR LIKELY BY MID/LATE
AFTERNOON. IN ADDITION TO POSING A THREAT FOR VERY LARGE
HAIL...ESPECIALLY IN THE HI PLNS E INTO CNTRL NEB/SE SD...A THREAT
ALSO WILL EXIST FOR TORNADOES. THE LATTER THREAT SHOULD BE GREATEST
DURING THE EARLY STAGES OF STORM DEVELOPMENT IN THE HI PLNS...AND
INVOF WARM FRONT FROM SE SD ESE INTO IA/SRN MN.
AFTN STORMS LIKELY WILL MERGE INTO SEVERAL CLUSTERS THIS EVE...ALONG
THE COLD FRONT AND LEE TROUGH IN PARTS OF SD...WRN/NRN NEB AND NW
KS...AND ALONG WARM FRONT IN IA/MN/IL. THE POTENTIAL WILL EXIST FOR
ONE OF THESE CLUSTERS TO GROW INTO A DERECHO LATE TONIGHT/EARLY
WED....MOST LIKELY OVER NERN NEB OR SE SD...AS 50+ KT 500 MB SPEED
MAX ASSOCIATED WITH THE GRT BASIN TROUGH OVERSPREADS THE REGION.
THIS CONVECTIVE SYSTEM COULD PRODUCE A SWATH OF DMGG WIND E/ESE INTO
NRN IL/SRN WI BY 12Z WED.
..HALES/SMITH.. 06/22/2010
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