SPC AC 271227
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0727 AM CDT SUN MAY 27 2007
VALID 271300Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM OH EWD ACROSS MUCH OF NY
AND PA...

...THERE IS A SLGT RISK OF SVR TSTMS PARTS OF CENTRAL/NRN HIGH
PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS PARTS OF SOUTHWEST AND SOUTH
CENTRAL MT...

...SYNOPSIS...
WESTERLIES REMAIN ACROSS NRN CONUS WITH A COUPLE MDT AMPLITUDE
TROUGHS AFFECTING THE U.S. THIS FORECAST PERIOD. UPPER SYSTEM AND
ASSOCIATED SURFACE LOW WILL TRACK EWD ACROSS SERN CANADA WITH
TRAILING COLD FRONT CURRENTLY FROM LAKE MICHIGAN SWWD TO NRN MO
MOVING EWD TO WRN NY SWWD TO VICINITY OH RIVER BY THIS EVENING.
UPSTREAM TROUGH NOW ENTERING PAC NW WILL INDUCE LEE CYCLOGENESIS
SERN MT THIS EVENING ALLOWING MOISTURE TO WORK NWD THRU WRN NEB/SD.
WEAK TROUGH SRN PLAINS AND RIDGE OVER SERN STATES CHANGE LITTLE.
NEAR SATURATED AIR MASS WILL MAINTAIN WIDESPREAD CONVECTIVE
POTENTIAL SRN PLAINS WITH LITTLE THREAT OF SEVERE STORMS GIVEN WEAK
SHEAR AND LIMITED INSTABILITY.

...UPPER OH VALLEY TO NERN STATES...
WITH PASSAGE OF TROUGH ACROSS ONTARIO INTO QUEBEC...A BAND OF
40-60KT WLYS AT MID LEVELS WILL SWEEP EWD ACROSS LOWER GREAT LAKES
INTO NY THIS AFTERNO0N AND EVENING. AHEAD OF THE COLD FRONT
MOISTURE IS SPREADING EWD FROM OH VALLEY WITH DEWPOINTS RISING INTO
THE LOW/MID 60S ACROSS WRN NY/PA BY EARLY THIS AFTERNOON. WITH MID
LEVEL LAPSE RATES AROUND 6C/KM...MLCAPES SHOULD GENERALLY RANGE
UPWARDS TO AROUND 1000-1500 J/KG WHERE SURFACE HEATING IS MAXIMIZED.
THUNDERSTORMS WILL INCREASE AHEAD OF COLD FRONT BY EARLY AFTERNOON
FROM LOWER LAKES WSWWD INTO UPPER OH VALLEY. 40-50KT OF DEEP LAYER
SHEAR SUPPORTS STORMS EVOLVING INTO SHORT LINES WHICH WILL ENHANCE
THE WIND DAMAGE POTENTIAL. LARGE HAIL POTENTIAL WILL BE SOMEWHAT
LIMITED BY AVAILABLE INSTABILITY AND WEAK LAPSE RATES. STORMS
SHOULD SPREAD E/SEWD ACROSS NY/NRN PA BY EVENING PRIOR TO WEAKENING
AFTER DARK.

...HIGH PLAINS FROM NWRN KS/ERN CO TO WRN SD...
AS LOW LEVEL MOISTURE RETURNS IN RESPONSE TO LEE TROUGHING...AIR
MASS HIGH PLAINS WILL BECOME MODERATELY UNSTABLE BY MID AFTERNOON.
WITH LAPSE RATES IN EXCESS OF 7C/KM MLCAPES WILL CLIMB TO 1500-2000
J/KG TODAY. THUNDERSTORMS WILL INITIALLY DEVELOP VICINITY THE WEAK
LEE TROUGH NERN CO TO WRN SD. WITH MARGINAL SHEAR ON THE ORDER OF
25-30 KT...STORM MODE SHOULD BE PREDOMINANTLY MULTICELLULAR WITH
ISOLATED SUPERCELLS. SEVERE THREAT SHOULD ALSO BE LIMITED TO LARGE
HAIL AND BRIEF DOWNBURSTS AS STORMS DEVELOP SLOWLY EWD DURING THE
EVENING.

...SOUTHWEST AND SOUTH CENTRAL MT...
WITH THE APPROACH OF THE STRONG TROUGH FROM PAC NW...CONDITIONS WILL
BECOME INCREASINGLY FAVORABLE FOR ORGANIZED CONVECTION BY LATER THIS
AFTERNOON SWRN MT. 40-50KT OF SHEAR AND 8C/KM LAPSE RATES SUGGEST
THAT SEVERE THUNDERSTORMS COULD OCCUR GIVEN ADEQUATE
MOISTURE/INSTABILITY. WHILE NAM MAY BE SOMEWHAT AGGRESSIVE ON
DESTABILIZATION...OBSERVED PWS FROM .6-.7 INCHES AHEAD OF TROUGH
SHOULD BE SUFFICIENT TO SUPPORT A FEW SEVERE THUNDERSTORMS BY LATE
THIS AFTERNOON SWRN MT...SPREADING ACROSS SCENTRAL MT BY EVENING.
GIVEN EXPECTED HIGH BASES...DAMAGING WINDS WOULD BE PRIMARY THREAT.
..HALES/JEWELL.. 05/27/2007