SWODY2
SPC AC 180539
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT FRI MAY 18 2007
VALID 191200Z - 201200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF MT...NRN WY
AND EXTREME SWRN SD...
..SYNOPSIS...
STRONG UPPER TROUGH WILL MOVE ACROSS THE PACIFIC NW ON SATURDAY...
WITH HEIGHT FALLS SPREADING EWD INTO THE NRN ROCKIES. AHEAD OF THIS
SYSTEM...A CANADIAN COLD FRONT WILL MOVE SWD THROUGH THE GREAT
LAKES/NRN PLAINS AND EDGE TOWARD THE DIVIDE IN MT. THIS BOUNDARY IS
FORECAST TO STRETCH FROM CENTRAL MT SEWD TO THE SD/NEB BORDER...AND
THEN EWD INTO LOWER MI BY LATE SATURDAY AFTERNOON.
ELSEWHERE...A SLOW MOVING COLD UPPER TROUGH OVER THE MID ATLANTIC
STATES WILL MAINTAIN SURFACE HIGH PRESSURE ACROSS MOST OF THE
SRN/ERN PORTIONS OF THE COUNTRY AND INHIBIT RICHER GULF MOISTURE
FROM RETURNING NWD INTO THE STATES DURING THIS PERIOD.
..MT...
APPROACHING UPPER TROUGH SHOULD RESULT IN LARGE SCALE LIFTING ACROSS
THE AREA...WITH STATIONARY FRONT PROVIDING FOCUS FOR THUNDERSTORMS
ACROSS WRN/CENTRAL MT BY LATE AFTERNOON. ALTHOUGH DEWPOINTS ARE
EXPECTED TO BE ONLY IN THE LOWER 50S...THESE DEWPOINTS COMBINED WITH
STEEP LAPSE RATES AND AFTERNOON TEMPERATURES IN THE 70S ARE EXPECTED
TO RESULT IN MLCAPES FROM 1500-2000 J/KG. WEAK ELY BOUNDARY LAYER
WINDS...VEERING TO WSWLY WITH HEIGHT...SHOULD PROVIDE SUFFICIENT
SHEAR FOR SUPERCELLS. THE RELATIVELY DRY BOUNDARY LAYER INDICATES
THAT HAIL AND WIND DAMAGE SHOULD BE THE MAIN THREATS.
THE STORMS ARE LIKELY TO SPREAD EWD INTO ERN MT/WRN ND OVERNIGHT AS
SLY LOW LEVEL JET DEVELOPS ACROSS WRN ND. HOWEVER...THESE STORMS
WILL BECOME PROGRESSIVELY MORE ELEVATED AND WEAKEN AS THEY SHIFT EWD
INTO THE DEEPER AND COOLER BOUNDARY LAYER LOCATED NORTH OF THE COLD
FRONT.
..NERN WY AND EXTREME SWRN SD...
FORCING AND SHEAR WILL BE WEAKER ACROSS THIS REGION THAN IN MT...
THOUGH STRONG HEATING ALONG THE FRONT SHOULD PROVIDE ENOUGH LIFT FOR
STORMS TO DEVELOP LATE IN THE DAY. ONCE STORMS DEVELOP... MODERATE
INSTABILITY AND STEEP LAPSE RATES WILL SUPPORT A FEW STORMS WITH A
SEVERE HAIL AND WIND DAMAGE POTENTIAL. WITH LOSS OF DAYTIME
HEATING/INSTABILITY...THESE STORMS SHOULD DIMINISH BY MID/LATE
EVENING.
..CENTRAL PLAINS/UPPER MS VALLEY...
DESPITE LACK OF LARGE SCALE FORCING AND RELATIVELY WEAK CONVERGENCE
ALONG COLD FRONT IN A CAPPED ENVIRONMENT...DIURNAL HEATING MAY BE
SUFFICIENT FOR A FEW STORMS TO DEVELOP ALONG THE FRONT LATE SATURDAY
AFTERNOON. THE STEEP LAPSE RATES...ESPECIALLY ACROSS SD/NEB...WILL
RESULT IN MODERATE INSTABILITY...SO ANY STORMS THAT DEVELOP WILL
HAVE THE POTENTIAL TO PRODUCE SEVERE WEATHER. SINCE UNCERTAINTY
EXISTS REGARDING HOW MANY STORMS WILL DEVELOP...ONLY LOW
PROBABILITIES ARE FORECAST ATTM.
..SRN FL PENINSULA...
SURFACE BOUNDARY IS FORECAST TO BE LOCATED ACROSS THE AREA AND GIVEN
MOIST ENVIRONMENT AND MLCAPES AROUND 1500 J/KG...SCATTERED
THUNDERSTORMS ARE EXPECTED. DEEP LAYER SHEAR MAY BE STRONG ENOUGH
FOR ISOLATED SEVERE STORMS DUE TO WLY WINDS ALOFT LOCATED ABOVE
RELATIVELY DEEP ELY BOUNDARY LAYER WINDS.
.IMY.. 05/18/2007
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