SPC AC 180556
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT THU MAY 18 2006
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MID-ATLANTIC REGION...
...SYNOPSIS...
FAIRLY STAGNANT LARGE SCALE PATTERN OF WRN MEAN RIDGE AND ERN TROUGH
WILL CONTINUE TO DOMINATE CONUS THROUGH PERIOD. SHORTWAVE TROUGH --
NOW DIGGING SEWD ACROSS LM AND ADJACENT PORTIONS IL/INDIANA -- IS
FCST TO EVOLVE INTO CLOSED LOW AS IT PIVOTS EWD ACROSS LOWER
MI...OH...LE...NWRN PA AND WRN NY.
AT SFC...COLD FRONT NOW MOVING SEWD ACROSS OH VALLEY REGION SHOULD
MOVE ACROSS CENTRAL/NRN APPALACHIANS EARLY IN PERIOD AND SRN
APPALACHIANS THEREAFTER. OCCLUDED SFC LOW SHOULD CONTINUE TO
RETROGRADE TOWARD POSITION OF MID/UPPER LEVEL CYCLONE.
LEE/PREFRONTAL SFC TROUGH IS ANALYZED FROM SERN ONT LOW SWD ACROSS
CENTRAL NY AND ERN PA...THEN SWWD GENERALLY ALONG PIEDMONT THROUGH
GA AND OVER W-CENTRAL FL PANHANDLE. THIS FEATURE SHOULD REMAIN
QUASISTATIONARY UNTIL CAUGHT BY SFC COLD FRONT -- FIRST OVER
MID-ATLANTIC STATES MID-DAY INTO AFTERNOON...THEN OVER CAROLINAS/GA
DURING EVENING.
WEAK SHORTWAVE PERTURBATION IS EVIDENT IN MOISTURE CHANNEL IMAGERY
OVER CENTRAL CA. AMONG OPERATIONAL AND ENSEMBLE MODEL RUNS FROM
17/21Z-18/00Z RUNS...THIS FEATURE WAS CLEARLY EVIDENT ONLY IN
OPERATIONAL SPECTRAL MODEL...WHICH REASONABLY PROGS IT TO DRIFT NWD
ACROSS PORTIONS CENTRAL/ERN ORE DURING MUCH OF THIS PERIOD.
...NRN NY THROUGH MID-ATLANTIC STATES...
SCATTERED TSTMS ARE EXPECTED IN ONE OR TWO PRIMARY BANDS INVOF SFC
TROUGH...ESPECIALLY ONCE FRONT MERGES WITH TROUGH. MAIN THREAT WILL
BE DAMAGING GUSTS...WITH MRGLLY SEVERE HAIL POSSIBLE.
ALTHOUGH SFC HEATING SHOULD NOT BE AS INTENSE AS FARTHER
S...COMBINATION OF MAXIMIZED BOUNDARY LAYER FORCING NEAR COMBINED
FRONT/LEE TROUGH AND FAVORABLE LAPSE RATES ALOFT WILL SUPPORT
CONVECTIVE POTENTIAL OVER THIS REGION. MODIFIED WRF AND ETA-KF
SOUNDINGS SUGGEST MID 50S SFC DEW POINTS WILL SUPPORT PRECONVECTIVE
MLCAPES 800-1200 J/KG IN HUDSON VALLEY REGION. ALTHOUGH LOW LEVEL
FLOW SHOULD BE WEAK...WINDS MAY BE BACKED IN DE/HUDSON RIVER
VALLEYS...AIDING DEEP-LAYER SHEAR AND STORM-RELATIVE INFLOW.
ALSO...MIDLEVEL WINDS SHOULD STRENGTHEN WITH TIME AS CYCLONE ALOFT
APCHS. SEVERE PROBABILITIES WILL DIMINISH EWD ACROSS NEW ENGLAND
AND ERN NJ AS DIURNAL HEATING WEAKENS AND AS MORE UPSTREAM AIR
EMANATES FROM COLD MARINE TRAJECTORIES.
...SRN PIEDMONT...
POSSIBILITY EXISTS FOR WIDELY SCATTERED TO SCATTERED TSTMS IN ONE OR
TWO BANDS...DEVELOPING INVOF SRN APPALACHIANS DURING AFTERNOON AND
MOVING EWD. MAIN CONCERN IS POTENTIAL FOR DAMAGING
GUSTS...SUPPORTED BY STRENGTHENING DEEP-LAYER SHEAR -- AMIDST NEARLY
UNIDIRECTIONAL DEEP-LAYER WIND PROFILES. HOWEVER...CONVECTIVE AND
SEVERE POTENTIAL IS MORE UNCERTAIN MAINLY BECAUSE OF ANTICIPATED
WEAK LEVELS OF BOTH BUOYANCY AND CONVERGENCE. MLCAPE SHOULD BE WEAK
OVER MOST OF AREA -- LESS THAN 500 J/KG -- BECAUSE OF COMBINATION OF
WEAK MIDLEVEL LAPSE RATES AND SEASONALLY LACKING MOISTURE...WITH SFC
DEW POINTS UPPER 40S TO MID 50S DURING DIURNAL MIXING PERIOD. IF
SUSTAINED/ORGANIZED CONVECTION DOES DEVELOP...RELATIVELY DRY
SUBCLOUD LAYER MAY ENHANCE POTENTIAL FOR DAMAGING GUSTS TO REACH
SFC. RIGHT NOW THREAT APPEARS TOO CONDITIONAL FOR CATEGORICAL
OUTLOOK.
...ORE...
WIDELY SCATTERED AFTERNOON TSTMS ARE EXPECTED...INITIALLY OVER
AREAS OF STRONGLY HEATED HIGHER TERRAIN WITH POTENTIAL TO SPREAD
INTO ADJACENT VALLEYS/BASINS. STEEP LOW-MIDDLE LEVEL LAPSE RATES
ALREADY EXIST OVER THIS REGION BASED ON LATEST RAOB DATA...AND WILL
BE ENHANCED BY COMBINATION OF SFC HEATING AND SUBTLE COOLING ALOFT
AHEAD OF SHORTWAVE TROUGH EMBEDDED IN SLY FLOW ALOFT. SFC DEW
POINTS 40S/50S F -- DEPENDING ON ELEVATION -- WILL COMBINE WITH 8-9
DEG C/KM LAPSE RATES TO YIELD MLCAPES NEAR 1000 J/KG IN SOME AREAS.
MAIN LIMITING FACTOR TO STORM ORGANIZATION -- AND PRECLUDING FACTOR
FOR CATEGORICAL OUTLOOK -- IS KINEMATIC WEAKNESS FROM SFC TO
MIDLEVELS.
...OH VALLEY...
COLD MIDLEVEL AIR MASS AND SFC HEATING BEHIND INITIAL CLOUD COVER
SHOULD SUPPORT WIDELY SCATTERED TSTMS LATE MORNING INTO EARLY
AFTERNOON. MAIN POTENTIAL WILL BE FOR HAIL...AS ACTIVITY PIVOTS
SEWD THEN EWD AROUND SRN PART OF COLD-CORE CYCLONIC VORTEX ALOFT.
THREAT SHOULD END QUICKLY WITH LOSS OF AFTERNOON HEATING.
..EDWARDS.. 05/18/2006
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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