ACUS02 KWNS 250552
SWODY2
SPC AC 250552
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT FRI SEP 25 2009
VALID 261200Z - 271200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS INDICATE THAT A STRENGTHENING POLAR JET STREAK...NOW OVER THE
NORTHERN PACIFIC...WILL GRADUALLY PROGRESS INLAND ACROSS THE
CANADIAN AND NORTHERN U.S. ROCKIES LATER TODAY THROUGH SATURDAY.
WITHIN THIS STREAM...A SHORT WAVE IMPULSE IS PROGGED TO DEVELOP AND
AMPLIFY TO THE LEE OF THE CANADIAN ROCKIES BY EARLY SATURDAY
...BEFORE DIGGING TOWARD THE CENTRAL INTERNATIONAL BORDER AREA
THROUGH EARLY SUNDAY. THIS FEATURE APPEARS LIKELY TO SUPPORT STRONG
SURFACE CYCLOGENESIS ACROSS THE SOUTH CENTRAL CANADIAN
PROVINCES...WHILE CONTRIBUTING TO THE EASTWARD ACCELERATION OF THE
REMNANTS OF THE UPPER CLOSED LOW NOW STILL CUT-OFF THE FROM THE
STRONGER WESTERLIES...ACROSS THE NORTH CENTRAL PLAINS. THE LATTER
FEATURE IS EXPECTED TO EVOLVE INTO A SHORT WAVE TROUGH AS IT SHIFTS
EAST OF THE MIDDLE MISSISSIPPI VALLEY TOWARD THE NORTHERN/CENTRAL
APPALACHIANS. THIS COULD SUPPORT WEAK SURFACE CYCLOGENESIS IN THE
WAKE OF A RETREATING SURFACE RIDGE ACROSS NORTH ATLANTIC COASTAL
AREAS. BUT...GUIDANCE SUGGESTS THAT THIS WILL NOT OCCUR UNTIL LATE
SATURDAY OR SATURDAY NIGHT...ALONG A RETREATING WARM FRONT TO THE
LEE OF THE SOUTH CENTRAL APPALACHIANS.
...CNTRL GULF STATES NORTHWARD THRU OHIO VALLEY...
ALTHOUGH A 50-70 KT CYCLONIC SOUTHWESTERLY 500 MB JET STREAK IS
PROGGED TO NOSE NORTHEASTWARD OUT OF THE OZARK PLATEAU THROUGH THE
OHIO VALLEY SATURDAY...MODELS INDICATE LITTLE IN THE WAY OF SURFACE
CYCLOGENESIS TO THE WEST OF THE APPALACHIANS...AND LOW-LEVEL WIND
FIELDS APPEAR LIKELY TO REMAIN GENERALLY WEAK. AN EXCEPTION MAY
EXIST WITHIN THE STRONGER GRADIENT ON THE WESTERN PERIPHERY OF THE
SURFACE RIDGE NEAR THE APPALACHIANS...BUT THIS IS EXPECTED TO BE
WITHIN GENERALLY COOLER/MORE STABLE AIR.
CONVECTIVE DEVELOPMENT MAY BE ONGOING EARLY IN THE DAY ACROSS
KENTUCKY/TENNESSEE...PERHAPS SOUTHWARD INTO PARTS OF THE LOWER
MISSISSIPPI VALLEY...IN ASSOCIATION WITH LARGE-SCALE FORCING AHEAD
OF THE UPPER TROUGH. HOWEVER...THIS MAY BE MOSTLY BASED WITHIN A
WEAKLY UNSTABLE ELEVATED WARM ADVECTION REGIME...WHICH IS EXPECTED
TO GRADUALLY SHIFT INTO/THROUGH THE CENTRAL APPALACHIANS DURING THE
DAY.
GUIDANCE IS SUGGESTIVE THAT BOUNDARY LAYER BASED DESTABILIZATION
WILL GENERALLY BE CONFINED TO PARTS OF SOUTHERN MISSISSIPPI...
ALABAMA AND CENTRAL/SOUTHERN GEORGIA DURING THE DAY. THIS
INSTABILITY...COUPLED WITH MID/UPPER FORCING...WILL PROBABLY BECOME
SUFFICIENT FOR CONSIDERABLE THUNDERSTORM ACTIVITY.
HOWEVER...DESPITE MIXED LAYER CAPE ON THE ORDER OF 1000+ J/KG...
WARM MOIST PROFILES CHARACTERIZED BY WEAK LAPSE RATES AND WEAK
LOW-LEVEL FLOW/SHEAR DO NOT APPEAR PARTICULARLY CONDUCIVE TO SEVERE
WIND OR HAIL. LOCALLY HEAVY RAINFALL SEEMS THE PRIMARY POTENTIAL
HAZARD IN THE PRESENCE OF HIGH MOISTURE CONTENT AIR WITH
PRECIPITABLE WATER UP TO 2+ INCHES.
...MIDDLE MISSISSIPPI VALLEY INTO AREAS NORTH OF THE OHIO RIVER...
STEEP MID-LEVEL LAPSE RATES AND COOL PROFILES NEAR A SIGNIFICANT
REMNANT CYCLONIC VORTICITY CENTER/MID-LEVEL COLD CORE SHIFTING EAST
NORTHEASTWARD OUT OF MISSOURI COULD CONTRIBUTE TO CONVECTIVE
POTENTIAL SATURDAY. AS THIS OVERSPREADS A BOUNDARY LAYER WARMED
BENEATH A PRECEDING MID-LEVEL DRY SLOT...THE ENVIRONMENT MAY BECOME
FAVORABLE FOR STORMS CAPABLE OF PRODUCING HAIL AND POTENTIALLY
DAMAGING WIND GUSTS...DESPITE LIMITED LOW-LEVEL MOISTURE. IF THIS
OCCURS /AND TOO MUCH UNCERTAINTY STILL EXISTS FOR SLIGHT RISK
PROBABILITIES/ THE THREAT SHOULD DIMINISH BY EARLY EVENING WITH THE
ONSET OF BOUNDARY LAYER COOLING.
...MID ATLANTIC STATES...
GIVEN THE LIKELIHOOD OF CONVECTIVE DEVELOPMENT IN THE PRESENCE OF
STRENGTHENING VERTICAL SHEAR...INCLUDING INCREASINGLY SIZABLE
CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS...NEAR THE DEVELOPING SURFACE
LOW SATURDAY NIGHT...AT LEAST LOW SEVERE PROBABILITIES APPEAR TO
EXIST ACROSS PARTS OF NORTH CAROLINA/VIRGINIA. DUE TO ANTICIPATED
WEAK MID-LEVEL LAPSE RATES...EVEN WITH CONSIDERABLE LOW-LEVEL
WARMING/MOISTENING...BOUNDARY LAYER DESTABILIZATION REMAINS THE
PRIMARY UNCERTAINTY CONCERNING THE POTENTIAL FOR TORNADOES OR
DAMAGING WIND GUSTS.
..KERR.. 09/25/2009
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