SWODY1
SPC AC 271630
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT FRI APR 27 2007
VALID 271630Z - 281200Z
..THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON FROM THE ERN
CAROLINAS INTO THE LOWER CHESAPEAKE REGION...
..MID ATLANTIC REGION THIS AFTERNOON...
MORNING WATER VAPOR IMAGERY SHOWS A COMPLEX MID LEVEL LOW OVER THE
GREAT LAKES...WITH SEVERAL SMALLER SCALE SPEED MAXIMA ROTATING
AROUND THE S/SE PERIPHERY OF THE LOW. ONE SUCH IMPULSE WILL MOVE
FROM N GA ACROSS THE CAROLINAS TO SE VA BY THIS EVENING...AS A WEAK
SURFACE COLD FRONT AND PRE-FRONTAL TROUGH MOVE EWD TO THE COAST BY
LATER TONIGHT. THESE SURFACE BOUNDARIES AND THE APPROACHING MID
LEVEL WAVE WILL PROVIDE A FAVORABLE ENVIRONMENT FOR THUNDERSTORM
DEVELOPMENT FROM THE CAROLINAS INTO VA THIS AFTERNOON.
REGIONAL 12Z SOUNDINGS REVEALED THE POTENTIAL FOR MODEST INSTABILITY
WITH DAYTIME HEATING /AFTERNOON MLCAPE VALUES OF 500-1000 J/KG BASED
ON SURFACE TEMPERATURES NEAR 80 F WITH MID 60S DEWPOINTS/...AND A
CAP NEAR 700 MB THAT SHOULD ERODE GRADUALLY WITH LOW-LEVEL MIXING
AND LOW-MID LEVEL ASCENT. IT APPEARS THAT THE WIDESPREAD CLOUDS AND
EARLY CONVECTIVE DEVELOPMENT IN SE VA SHOULD LIMIT THE NWD EXTENT OF
THE INSTABILITY THIS AFTERNOON. MEANWHILE...WARM SECTOR WIND
PROFILES SHOULD BE CHARACTERIZED BY LARGELY UNIDIRECTIONAL FLOW WITH
MODEST SPEED SHEAR THROUGH THE LOW-MID LEVELS...WHICH SHOULD SUPPORT
A FEW SUPERCELLS AND/OR SHORT BOWING SEGMENTS CAPABLE OF PRODUCING
DAMAGING WINDS AND PERHAPS A TORNADO OR TWO. OTHERWISE...MARGINALLY
SEVERE HAIL MAY ACCOMPANY THE MORE INTENSE STORMS THIS AFTERNOON.
..W TX/OK AREA THIS AFTERNOON/EVENING...
A PRONOUNCED MID LEVEL SHORTWAVE OVER SRN NEB/NRN KS WILL PROGRESS
SEWD TO MO/NRN AR BY EARLY TONIGHT. THE STRONGEST FORCING FOR
ASCENT WILL GENERALLY BE CONFINED TO AREAS FROM ERN KS/NE OK
NEWD...WHILE A BELT OF WAA FROM THE WSW SPREADS SEWD ACROSS OK
DURING THE DAY. REGIONAL 12Z SOUNDINGS SHOW ONLY LIMITED POTENTIAL
FOR INSTABILITY WITH THE RICHER LOW-LEVEL MOISTURE AND STEEPER MID
LEVEL LAPSE RATES CONFINED TO AREAS OF S AND W TX. MEAN BOUNDARY
LAYER DEWPOINTS ARE UNLIKELY TO EXCEED THE LOW-MID 50S FROM CENTRAL
TX INTO OK...AND ONLY WEAK INSTABILITY IS EXPECTED WITH AFTERNOON
SURFACE TEMPERATURES OF 75-80 F FROM SW OK INTO NW TX. IF SURFACE
HEATING/MIXING CAN SUFFICIENTLY WEAKEN THE CAP ALONG THE SURFACE
BOUNDARY AND IN THE WAKE OF THE EARLY ELEVATED STORMS...ISOLATED
HIGH-BASED SUPERCELLS WILL BE POSSIBLE. HOWEVER...CONFIDENCE IN
SURFACE-BASED DEVELOPMENT IS LOW AND THE OVERALL SEVERE THREAT
APPEARS TOO MARGINAL TO WARRANT MORE THAN LOW SEVERE PROBABILITIES.
FARTHER SW...STRONGER HEATING/DEEPER MIXING MAY ALLOW THE CAP TO
ERODE SUFFICIENTLY FOR ISOLATED THUNDERSTORM DEVELOPMENT THIS
AFTERNOON ALONG THE WEAK INVERTED TROUGH/COLD FRONT INTO W TX.
LIMITED MOISTURE AND WEAKER VERTICAL SHEAR COMPARED TO AREAS FARTHER
N SUGGEST THAT ANY SEVERE STORM THREAT IN THIS AREA WILL ALSO REMAIN
ISOLATED/MARGINAL.
.THOMPSON/GRAMS.. 04/27/2007
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