SPC AC 020552
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT THU APR 02 2009
VALID 031200Z - 041200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
LARGE SCALE UPPER AIR PATTERN WILL CONTINUE TO CONTAIN MEAN/LONGWAVE
TROUGHING OVER CENTRAL CONUS AND RIDGING OVER NERN PACIFIC.
PROGRESSIVE SERIES OF STG SHORTWAVE TROUGHS WILL CONTINUE TO TRACK
SEWD FROM NERN PACIFIC AND NEWD OUT OF CENTRAL CONUS RIDGE. ONE OF
THESE TROUGHS IS DEVELOPING SMALL/COMPACT/CLOSED LOW ATTM OVER NERN
NM/TX PANHANDLE REGION. THIS FEATURE IS FCST INVOF SRN OH/ERN
KY/SWRN WV AT START OF PERIOD...LIFTING NEWD TO ERN NY OR NEW
ENGLAND BY 4/12Z. ASSOCIATED SFC COLD FRONT SHOULD MOVE OFFSHORE
CAROLINAS/GA BETWEEN END OF DAY-1 PERIOD AND ABOUT 03/15Z.
IMPORTANT MESOSCALE VARIATIONS LINGER IN PROGS REGARDING TIMING OF
FROPA ALONG COASTLINE...WITH SPECTRAL/UKMET FASTER...BUT WITH
OPERATIONAL NAM AND STG SREF CONSENSUS A FEW HOURS SLOWER. TRAILING
PORTION OF THIS FRONT IS FCST TO MOVE SWD ACROSS NRN/CENTRAL FL BUT
DECELERATE AND WEAKEN THROUGH PERIOD...AS STRONGEST DEEP-LAYER
FORCING MOVES NEWD WELL AWAY FROM THIS AREA. NRN PORTION OF FRONT
SHOULD MOVE ENEWD-NEWD OVER DELMARVA/MID-ATLANTIC REGION THROUGH
MID-DAY INTO AFTERNOON...LIKELY AS OCCLUDED BOUNDARY.
MEANWHILE...MID-UPPER LEVEL SHORTWAVE TROUGHS -- NOW EVIDENT IN
MOISTURE CHANNEL IMAGERY OFFSHORE PACIFIC NW AND OVER GULF OF AK --
ARE EXPECTED TO COMBINE TO YIELD STG TROUGH AND EMBEDDED/CLOSED 500
MB LOW OVER GREAT BASIN BY 4/00Z. RESULTING MID-UPPER LEVEL LOW
THEN SHOULD DIG ACROSS 4-CORNERS/SWRN CO AREA AND MOVE TO VICINITY
SERN CO/SWRN KS BY END OF PERIOD. LARGE SCALE ASCENT WITH STG
COOLING ALOFT...OVER MRGL LOW-MIDLEVEL MOISTURE...WILL SUPPORT GEN
TSTM POTENTIAL OVER BROAD SWATH OF W-CENTRAL CONUS AND GREAT BASIN
REGION. STG LOW LEVEL WAA IS EXPECTED OVER GREAT PLAINS IN ADVANCE
OF THIS FEATURE...AND VERY ELEVATED TSTMS MAY DEVELOP NEAR END OF
PERIOD ACROSS PORTIONS CENTRAL PLAINS AS STG/DEEP ISENTROPIC ASCENT
RAISES PARCELS TO LFC...WITH MINIMAL CAPE. MOISTURE SHOULD REMAIN
TOO SCANT TO SUPPORT ORGANIZED SVR THREAT UNTIL AFTER END OF PERIOD.
...COASTAL CAROLINAS...EARLY PERIOD...
STG DEEP-LAYER SPEED SHEAR AND AT LEAST MARGINAL SFC-BASED BUOYANCY
ARE EXPECTED AHEAD OF COLD FRONT...IN SUPPORT OF CONDITIONAL
POTENTIAL FOR SVR. CONSIDERABLE UNCERTAINTIES REMAIN ABOUT NOT ONLY
FRONTAL POSITION/TIMING ON MESOSCALE OVER THIS REGION...BUT
ALSO...POTENTIAL FOR PREFERENTIAL CONVECTIVE DEVELOPMENT OFFSHORE
INSTEAD OF ALONG IMMEDIATE FRONT. PREFRONTAL CONVERGENCE BAND MAY
DEVELOP OVER ADJOINING PORTIONS ATLANTIC...ATOP BOUNDARY LAYER
THETAE PLUME ENRICHED BY AIR/SEA THERMODYNAMIC FLUXES...PERHAPS
REDUCING INLAND POTENTIAL.
...DELMARVA/ERN VA TO MID-ATLANTIC...DIURNAL...
NARROW/LOW-TOPPED BAND OF CONVECTION MAY DEVELOP ALONG COLD/OCCLUDED
FRONT AND LIFT NEWD ACROSS THIS REGION WITH POTENTIAL FOR STG-SVR
GUSTS IN SOME LOCALES. WARM/COLD FRONTAL TRIPLE POINT -- AND
THEREFORE MOST FAVORABLY BUOYANT WARM SECTOR -- CURRENTLY ARE
PROGGED TO REMAIN OFFSHORE. HOWEVER...FCST SOUNDINGS SUGGEST SOME
POTENTIAL FOR DIABATIC HEATING OF AT LEAST MRGLLY MOIST/UNSTABLE
AMBIENT AIR MASS OVER DELMARVA...PERHAPS WWD INTO ERN VA AND NWD UP
DE VALLEY DEPENDING ON AMBIENT CLOUD COVER AND PRECIP PATTERNS.
ACTIVITY MAY BEGIN EARLY IN PERIOD...IN NEUTRALLY TO VERY WEAKLY
UNSTABLE AIR MASS...THEN MOVE EWD INTO POCKETS OF MORE BUOYANT AIR
DURING AFTERNOON. VERY STG BUT NEARLY UNIDIRECTIONAL DEEP-LAYER
WINDS INDICATE POTENTIAL FOR LINEAR MODE WITH CONVECTIVE GUSTS BEING
MAIN CONCERN. POTENTIAL APPEARS TOO CONDITIONAL ON MESOSCALE
FACTORS FOR CATEGORICAL RISK ATTM...BUT WILL INTRODUCE MRGL SVR
PROBABILITIES FOR NOW.
...FL...DIURNAL...
BAND OF CONVECTION MAY BE ONGOING ALONG OR JUST AHEAD OF COLD FRONT
AT BEGINNING OF PERIOD...OVER PORTIONS NRN/CENTRAL FL. FAVORABLE
DEEP-LAYER SHEAR -- MAINLY SPEED SHEAR GIVEN WLY PREFRONTAL WIND
COMPONENT -- IS EXPECTED BETWEEN 3/12Z AND 3/18Z. STRONGEST WIND
FIELDS WILL COINCIDE WITH MORNING MIN OF BOUNDARY LAYER
INSTABILITY...BUT MAY REMAIN FAVORABLE FOR SVR INTO AFTERNOON
DESPITE GEN DECREASING TREND WITH TIME. FOREGOING AIR MASS IS FCST
TO UNDERGO STG DIABATIC SFC HEATING ...BUT COINCIDENT WITH WEAKENING
OF BOTH FRONTAL CONVERGENCE AND LOW LEVEL SHEAR. PORTIONS CENTRAL
FL MAY REQUIRE UPGRADE ONCE RELATIVE BALANCE OF THESE OFFSETTING
TRENDS BECOMES MORE CERTAIN.
..EDWARDS.. 04/02/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
|
