SPC AC 081954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT THU APR 08 2010
VALID 082000Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE LOWER GREAT
LAKES INTO GA AND THE FL PNHDL...
...UPSTATE NY...
TORNADO PROBABILITIES HAVE BEEN INCREASED TO FIVE PERCENT INVOF OF
RETREATING WARM FRONT AND IN ADVANCE OF WEAK SURFACE LOW WHICH WILL
DEVELOP EWD INTO CNTRL NY BY EARLY EVENING.
WHILE PARTLY CLOUDY SKIES HAVE ALLOWED FOR TEMPERATURES TO WARM INTO
THE 70S AND 80S...DEEPER BOUNDARY LAYER MIXING IS RESULTING IN
DECREASING MOISTURE CONTENT WHICH WILL EFFECTIVELY LIMIT MLCAPE TO
LESS THAN 500-1000 J/KG. THE MIXING OF BOUNDARY LAYER MOISTURE MAY
BE SOMEWHAT MORE SHELTERED ALONG WARM FRONT WHERE LOW-LEVEL SHEAR
WILL REMAIN LOCALLY ENHANCED DUE TO BACKED NEAR-SURFACE WINDS. AS
SUCH...SOME POTENTIAL FOR A TORNADO OR TWO WILL EXIST WITH ANY
ROTATING STORMS THAT CAN INTERACT WITH THE FAVORABLE ENVIRONMENT.
OTHERWISE...EXPECT THAT DAMAGING WINDS WILL REMAIN THE PRIMARY
SEVERE WEATHER HAZARD WITH STORMS DEVELOPING ALONG AND AHEAD OF COLD
FRONT THIS AFTERNOON INTO EVENING.
...PIEDMONT REGION FROM THE DELMARVA INTO N-CNTRL SC...
WIND PROBABILITIES HAVE BEEN LOWERED TO 15 PERCENT ACROSS THE
REGION.
STEEP LOW-LEVEL LAPSE RATES HAVE DEVELOPED ACROSS THE PIEDMONT AND
COASTAL PLAINS THIS AFTERNOON IN CONJUNCTION WITH STRONG DIABATIC
HEATING THAT HAS OCCURRED SO FAR TODAY. HOWEVER SIMILAR TO PREVIOUS
SECTION...DEEPER BOUNDARY LAYER MIXING IS RESULTING IN DECREASING
MOISTURE CONTENT...AND THIS SHOULD LIMIT MLCAPE TO 500-1000 J/KG
THROUGH THE REMAINDER OF THE DIURNAL HEATING CYCLE. SCATTERED TSTMS
STILL APPEAR LIKELY TO DEVELOP ALONG COLD FRONT EMERGING FROM THE
BLUE RIDGE THIS AFTERNOON. AND GIVEN THE INCREASING...DEEP SWLY
WIND FIELD AND DEEPENING...DRYING BOUNDARY LAYER...DAMAGING WINDS
WILL REMAIN POSSIBLE WITH THE MOST INTENSE STORMS INTO THIS EVENING.
...FL PNHDL/GA INTO CNTRL SC...
HIGHER TORNADO PROBABILITIES HAVE BEEN EXTENDED NEWD INTO CNTRL SC.
PRE-FRONTAL AIR MASS REMAINS MORE MOIST ACROSS THIS AREA WHERE
DEWPOINTS REMAIN IN THE 60S. THIS MOIST...UNCAPPED ENVIRONMENT...IN
CONCERT WITH INCREASED FORCING FOR ASCENT ASSOCIATED WITH VORTICITY
MAXIMUM CURRENTLY MOVING THROUGH THE CNTRL GULF COAST STATES ARE
SERVING TO MAINTAIN ONGOING CLUSTERS OF TSTMS...SOME OF WHICH HAVE
EXHIBITED SUPERCELL CHARACTERISTICS.
REGIONAL VWPS INDICATE SUFFICIENT LOW AND DEEP-LAYER SHEAR TO
SUPPORT A CONTINUED THREAT FOR UPDRAFT ROTATION. THIS STRONGER
LOW-LEVEL SHEAR WILL TEND TO WEAKEN FROM SW-NE ACROSS THE REGION
WITH THE NEWD MIGRATION OF 40-50 KT LLJ. AS SUCH...EXPECT THE
THREAT FOR ISOLATED TORNADOES TO BEGIN TO DECREASE OVER SWRN GA AND
THE FL PNHDL BY LATE AFTERNOON/EARLY EVENING. OVER PARTS OF
CNTRL/NERN GA INTO CNTRL SC...THIS THREAT WILL LIKELY CONTINUE
THROUGH THE EVENING HOURS.
..MEAD.. 04/08/2010
.PREV DISCUSSION... /ISSUED 1250 PM CDT THU APR 08 2010/
AMENDED TO INCREASE TORNADO PROBABILITIES FROM THE FL PANHANDLE INTO
SWRN GA
...FL PANHANDLE INTO THE CAROLINAS...MID ATLANTIC AND NERN STATES...
SYNOPTIC SCALE UPPER TROUGH FROM THE GREAT LAKES SWD THROUGH THE TN
AND LOWER MS VALLEYS WILL MOVE SLOWLY EAST TODAY. SURFACE LOW OVER
THE GREAT LAKES WILL LIFT INTO SERN ONTARIO IN ASSOCIATION WITH A
VORT MAX EJECTING NNEWD ALONG ERN PERIPHERY OF THE UPPER TROUGH.
TRAILING COLD FRONT WILL CONTINUE EWD THROUGH THE OH AND TN VALLEYS
AND SERN STATES...REACHING THE ATLANTIC SEABOARD TOWARD THE END OF
THE PERIOD. A WARM FRONT EXTENDING EWD FROM THE LOW WILL LIFT NWD
THROUGH MUCH OF NY.
EARLY THIS AFTERNOON AN EXTENSIVE BAND OF PRE-FRONTAL CONVECTION
PERSISTS FROM ERN OH SWD THROUGH ERN TN INTO SERN GA. MODIFIED CP
AIR WITH MOSTLY 50S DEWPOINTS HAS ADVECTED NWD THROUGH WARM SECTOR
BENEATH 7 C/KM 700-500 MB LAPSE RATES ACROSS THE CAROLINAS...MID
ATLANTIC AND NERN STATES. LOW 60S DEWPOINTS EXIST FARTHER SOUTH
ACROSS THE FL PANHANDLE...SRN GA AND THE COASTAL CAROLINAS. CLEAR TO
PARTLY CLOUDY SKIES EAST OF THE ONGOING CONVECTION WILL ALLOW FOR
STRONG DIABATIC WARMING...BUT LIMITED BOUNDARY LAYER MOISTURE WILL
RESULT IN MLCAPE AOB 500 J/KG OVER MUCH OF SLIGHT RISK AREA...EXCEPT
NEAR 1000 J/KG ACROSS PARTS OF SRN GA AND THE FL PANHANDLE.
STORMS WILL CONTINUE DEVELOPING ALONG AND JUST AHEAD OF PRE-FRONTAL
CONVECTIVE BOUNDARIES AS THE ATMOSPHERE DESTABILIZES DOWNSTREAM.
STRONGER SWLY LOW LEVEL JET IS FORECAST TO DEVELOP NEWD THROUGH THE
CAROLINAS AND MID ATLANTIC THROUGH THE DAY. HOWEVER...WITH THE
EXCEPTION OF PROXIMITY TO WARM FRONT OVER NY...NEAR SURFACE WINDS
SHOULD REMAIN SLIGHTLY VEERED TO SSWLY WHICH WILL TEND TO LIMIT 0-1
KM HODOGRAPH SIZE. STRONG SWLY MID-UPPER FLOW AHEAD OF THE
PROGRESSIVE UPPER TROUGH WILL CONTRIBUTE TO 40-50 KT DEEP LAYER
SHEAR IN MUCH OF THE WARM SECTOR. ORGANIZED STORMS INCLUDING BOWING
LINE SEGMENTS AND SUPERCELLS WILL BE POSSIBLE. WHILE LIMITED
MOISTURE WILL REDUCE MAGNITUDE OF EXPECTED INSTABILITY...THE DRIER
BOUNDARY LAYERS MAY ENHANCE POTENTIAL FOR DAMAGING WIND AS STORMS
INCREASE DURING THE AFTERNOON. THE DAMAGING WIND THREAT MAY BE
SOMEWHAT HIGHER FROM THE CAROLINAS INTO THE MID-ATLANTIC WHERE THE
STRONGEST LOW LEVEL JET IS FORECAST TO EXIST DURING PEAK HEATING.
WHILE PRIMARY THREAT APPEARS TO BE DAMAGING WIND...AN ISOLATED
TORNADO OR TWO CANNOT BE RULED OUT...ESPECIALLY OVER SRN PARTS OF
THE SLIGHT RISK AREA WHERE GREATER BOUNDARY LAYER MOISTURE EXISTS.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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