SWODY1
SPC AC 201543
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1043 AM CDT SUN APR 20 2008
VALID 201630Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF EASTERN VA AND
EASTERN NC...
...VA/NC...
REF MCD 669
MORNING WATER VAPOR IMAGERY SHOWS A DEEP UPPER LOW CENTERED OVER
EASTERN KY...WITH SEVERAL SMALLER SCALE VORTICITY AXES ROTATING
AROUND LOW. ONE OR MORE OF THESE SMALLER PERTURBATIONS WILL AFFECT
THE MID ATLANTIC AND CAROLINAS REGIONS TODAY. A PLUME OF RELATIVELY
DEEP MOISTURE IS PRESENT THIS MORNING FROM EASTERN NC/EASTERN VA
INTO PARTS OF MD AND CENTRAL PA. DESPITE PERSISTENT CLOUD COVER IN
THIS ZONE...RATHER COOL TEMPERATURES ALOFT AND DEWPOINTS IN THE
UPPER 50S TO LOWER 60S WILL HELP RESULT IN MLCAPE VALUES OF UP TO
500 J/KG LATER THIS AFTERNOON. FORECAST SOUNDINGS SHOW BACKED LOW
LEVEL WINDS OVER THIS AREA...PROVIDING SUFFICIENT LOW LEVEL/DEEP
LAYER VERTICAL SHEAR FOR THUNDERSTORM ORGANIZATION AND POSSIBLE
SUPERCELLS DESPITE RATHER WEAK INSTABILITY. PRESENT INDICATIONS
REMAIN THAT STRONGER CELLS ALONG AN AXIS FROM DCA-EASTERN NC WILL BE
CAPABLE OF BRIEF TORNADOES AND GUSTY WINDS THIS AFTERNOON AND EARLY
EVENING.
A FEW STRONG STORMS ARE ALSO POSSIBLE THIS AFTERNOON ACROSS PARTS OF
WV AND WESTERN VA/NC BENEATH COLD UPPER LOW. THERMODYNAMIC PROFILES
IN THIS AREA SUGGEST A RISK OF HAIL IN MORE INTENSE UPDRAFTS TODAY.
...DAKOTAS...
VIGOROUS S/WV TROUGH/MID LEVEL WIND MAX ROTATES NEWD FROM NRN
INTERMOUNTAIN REGION TO NRN HIGH PLAINS THIS EVE AND INTO SRN CANADA
BY 12Z MON. THE STRONG COLD FRONT NOW VICINITY ND/MT BORDER SWWD
INTO CENTRAL WY MOVES ONLY SLOWLY EWD THIS AFTERNOON AS SURFACE LOW
DEEPENS WRN SD.
STRONG 40-50KT SSELY LLJ AHEAD OF FRONT ACROSS DAKOTAS WILL BRING A
LITTLE LOW LEVEL MOISTURE NWD TODAY...WHICH COUPLED WITH THE VERY
STEEP LAPSE RATES WILL DEVELOP A SMALL AMOUNT OF MLCAPE ATOP A DEEP
MIXED LAYER BY LATER THIS AFTERNOON. HIGH BASED THUNDERSTORMS WILL
DEVELOP BY MID/LATE AFTERNOON ALONG AND JUST AHEAD OF SLOW MOVING
COLD FRONT AND WITH STRONG UPPER SUPPORT PRODUCE AT LEAST A
POTENTIAL FOR ISOLATED SEVERE STORMS.
WITH SUCH A VIGOROUS S/WV IMPULSE AND THE STEEP LAPSE RATES IN
EXCESS OF 8C/KM...THERE WILL BE AT A LOW END DAMAGING WIND THREAT
THIS EVENING AS STORMS WILL TEND TO LINE UP ALONG FRONTAL BOUNDARY
AS THEY MOVE NEWD ACROSS WRN ND SWD INTO SD..
..HALES/HURLBUT.. 04/20/2008
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