SWODY2
SPC AC 251723
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1223 PM CDT WED APR 25 2007
VALID 261200Z - 271200Z
..THERE IS A SLGT RISK OF SVR TSTMS THU/THU EVE ACROSS PARTS OF THE
ERN GULF STATES...OH VALLEY...NRN/CNTRL APPALACHIANS AND MID
ATLANTIC COAST STATES....
..SYNOPSIS...
AMPLIFICATION IN THE UPPER FLOW PATTERN NOW APPEARS UNDERWAY ACROSS
THE EASTERN PACIFIC...AND MODELS INDICATE THAT AN UPPER RIDGE WILL
CONTINUE TO BUILD NORTHEASTWARD INTO THE PACIFIC COAST
STATES/NORTHERN INTERMOUNTAIN REGION THURSDAY/THURSDAY NIGHT. AS
THIS OCCURS...UPPER TROUGH NOW PROGRESSING INTO THE PACIFIC COAST IS
FORECAST TO SPLIT...WITH ONE IMPULSE DIGGING INTO THE SOUTHERN
PLATEAU/BAJA REGION...AND ANOTHER ACROSS THE NORTH CENTRAL ROCKIES.
A THIRD IMPULSE IS PROGGED TO CONTINUE EASTWARD WITHIN STRONGER
NORTHERN BRANCH OF THE WESTERLIES...ACROSS THE CANADIAN PROVINCES.
AND...THE BROAD DOWNSTREAM SOUTHERN BRANCH CLOSED LOW IS PROGGED TO
ACCELERATE NORTHEASTWARD OUT OF THE MIDDLE/LOWER MISSISSIPPI VALLEY
REGION.
A SIGNIFICANT SURFACE LOW ACCOMPANYING THE LATTER FEATURE APPEARS
LIKELY TO MIGRATE FROM THE MIDDLE MISSISSIPPI/LOWER OHIO VALLEY
THROUGH THE GREAT LAKES REGION...WITH THE PRIMARY SURFACE COLD FRONT
ADVANCING TO ITS SOUTH/EAST...TOWARD THE APPALACHIANS. MODELS
INDICATE THAT A SURFACE FRONT...STALLING TO THE LEE OF THE CENTRAL
APPALACHIANS TODAY...WILL RETREAT NORTHWARD THROUGH THE NORTHERN MID
ATLANTIC COAST STATES...BUT THIS MAY NOT OCCUR UNTIL LATE THURSDAY
OR THURSDAY NIGHT.
..EASTERN STATES...
AN INFLUX OF 60F+ SURFACE DEW POINTS OFF THE GULF OF MEXICO IS
ANTICIPATED AHEAD OF THE COLD FRONT TO THE WEST OF THE
APPALACHIANS...WITH AN INCREASE IN MOISTURE ALSO EXPECTED ON
SOUTHERLY FLOW OFF THE WESTERN ATLANTIC INTO THE LEE OF THE
APPALACHIANS. HOWEVER...DESTABILIZATION SEEMS LIKELY TO BE LIMITED
BY CONSIDERABLE CLOUD COVER/CONVECTION...WHICH MAY BE ONGOING AT 12Z
THURSDAY...PARTICULARLY TO THE WEST OF THE APPALACHIANS.
THE MOST SIGNIFICANT OF THE EARLY MORNING CONVECTION PROBABLY WILL
BE OCCURRING IN PRE-FRONTAL CONFLUENT BAND NEAR A 30-50 KT SOUTHERLY
LOW-LEVEL JET AXIS...ACROSS SOUTHEAST MISSISSIPPI THROUGH CENTRAL
ALABAMA. LARGE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS WILL SUPPORT
RISK OF SUPERCELLS WITH TORNADOES...IN A WEAKLY UNSTABLE BUT DEEP
MOIST BOUNDARY LAYER. DAMAGING WIND GUSTS MAY ALSO ACCOMPANY A
BROKEN SQUALL LINE AS IT SLOWLY ADVANCES EASTWARD THROUGH
NORTHERN/WESTERN GEORGIA DURING THE DAYTIME HOURS.
STRONGER MID/UPPER FORCING ASSOCIATED WITH EVOLVING LARGE-SCALE
PATTERN WILL SPREAD NORTHEAST OF THE LOWER OHIO/TENNESSEE VALLEYS
EARLY THURSDAY. AND...THIS IS EXPECTED TO CONTRIBUTE TO
CONSIDERABLE...PERHAPS VIGOROUS...THUNDERSTORM ACTIVITY THURSDAY
AFTERNOON INTO THURSDAY NIGHT. THE BEST CHANCE FOR APPRECIABLE
SURFACE HEATING/BOUNDARY LAYER DESTABILIZATION SEEMS TO BE IN FAIRLY
CLOSE PROXIMITY TO THE WESTERN SLOPES OF THE APPALACHIANS ...AND IN
A SURFACE TROUGH TO THE IMMEDIATE LEE OF THE SOUTH CENTRAL
APPALACHIANS...ACROSS NORTH CAROLINA INTO THE VICINITY OF WARM
FRONTAL ZONE ACROSS SOUTHWEST VIRGINIA. 50-70KT SOUTHWESTERLY 500
MB FLOW TO THE EAST OF UPPER TROUGH ACROSS THE CENTRAL APPALACHIANS
WILL CONTRIBUTE TO FAVORABLE DEEP LAYER SHEAR FOR SUPERCELLS.
AS 30-50 KT SOUTHERLY LOW-LEVEL JET DEVELOPS NORTHEASTWARD ACROSS
EASTERN KENTUCKY INTO PARTS OF SOUTHEAST OHIO/WESTERN WEST VIRGINIA
AND WESTERN PENNSYLVANIA DURING THE LATE AFTERNOON... LOW-LEVEL
HODOGRAPHS WILL BECOME SUFFICIENTLY ENLARGED TO ENHANCE A RISK FOR
TORNADOES...IN ADDITION TO DAMAGING WINDS/MARGINAL SEVERE HAIL.
MODELS ARE SUGGESTIVE THAT THIS BELT OF STRONGER LOW-LEVEL FLOW WILL
DEVELOP TO THE LEE OF THE CENTRAL APPALACHIANS CLOSER TO/SHORTLY
AFTER 27/00Z. AND...A LINGERING SOUTHEASTERLY COMPONENT TO THE
SURFACE FLOW IS EXPECTED TO CONTRIBUTE TO LARGE CLOCKWISE CURVED
HODOGRAPHS...WITH POTENTIAL FOR AT LEAST ISOLATED TORNADOES
INCREASING DURING THE EVENING HOURS.
.KERR.. 04/25/2007
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