SWODY2
SPC AC 281722
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1222 PM CDT THU MAY 28 2009
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS FRI ACROSS PARTS OF THE MID
ATLANTIC STATES....
...SYNOPSIS...
AMPLIFICATION WITHIN THE MAIN BELT OF POLAR WESTERLIES NEAR THE
CANADIAN/U.S. BORDER AREA NOW APPEARS UNDERWAY...WITH A RIDGE
BUILDING ACROSS THE CANADIAN ROCKIES AND A TROUGH DEVELOPING ACROSS
THE CENTRAL CANADIAN PROVINCES INTO THE UPPER GREAT LAKES REGION.
MODELS SUGGEST THAT THE WESTERN RIDGING WILL BE SUPPRESSED FRIDAY AS
A SIGNIFICANT SHORT WAVE IMPULSE MIGRATES INLAND ACROSS THE BRITISH
COLUMBIA COAST. HOWEVER...THE EASTERN TROUGH IS PROGGED TO CONTINUE
TO AMPLIFY...AS AN INITIAL SHORT WAVE TROUGH DIGS THROUGH THE GREAT
LAKES REGION...AND THE HUDSON BAY VORTEX REFORMS SOUTHWARD ACROSS
ONTARIO IN RESPONSE TO A SIGNIFICANT IMPULSE ROTATING AROUND ITS
WESTERN/SOUTHERN PERIPHERY.
TO THE SOUTH OF THIS REGIME...MID/UPPER FLOW WILL REMAIN GENERALLY
WEAK...AND BROADLY CYCLONIC ACROSS THE WESTERN GULF STATES/LOWER
MISSISSIPPI VALLEY AND SOUTHEAST. MID/UPPER RIDGING IS EXPECTED TO
PERSIST ACROSS THE INTERMOUNTAIN WEST AND ROCKIES...WITH A LINGERING
HIGH CENTER OVER THE NORTHERN GREAT BASIN. BUT...A SUBTROPICAL LOW
IS PROGGED TO CONTINUE GRADUALLY MIGRATING INTO THE SOUTHERN
CALIFORNIA/NORTHERN BAJA VICINITY...WHILE A MUCH STRONGER LOW
REMAINS CUT-OFF FROM THE POLAR WESTERLIES...WELL WEST OF PACIFIC
COASTAL AREAS.
ASSOCIATED WITH THE EVOLVING PATTERN...AN INFLUX OF COOLER...DRIER
AIR INTO A LARGE PORTION OF THE SOUTH CENTRAL AND SOUTHEASTERN U.S.
WILL RESULT IN A CONTINUED LOWERING OF CONVECTIVE POTENTIAL INTO
FRIDAY. HOWEVER...THUNDERSTORMS ARE EXPECTED TO AGAIN BE NUMEROUS
TO THE EAST AND SOUTH OF THE FRONT...ACROSS MUCH OF THE ATLANTIC
SEABOARD...AND ACROSS THE HIGHER TERRAIN OF NORTHEAST MEXICO INTO
PARTS OF SOUTHWEST TEXAS AND THE LOWER RIO GRANDE VALLEY. ACROSS
THE WEST...WEAK LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION AND
MOISTENING WILL AID CONVECTIVE DEVELOPMENT ACROSS THE HIGHER
TERRAIN...MAINLY AROUND THE PERIPHERY OF THE UPPER HIGH CENTER.
...MID ATLANTIC STATES...
WEAK TO MODERATE DESTABILIZATION...WEAK INHIBITION AND FAVORABLE
LARGE-SCALE FORCING AHEAD OF AMPLIFYING UPPER TROUGH PROBABLY WILL
SUPPORT CONSIDERABLE THUNDERSTORM ACTIVITY FRIDAY...MAINLY ALONG/
EAST OF THE LEE SURFACE TROUGH. DESPITE THE WEAK NATURE OF THE
LOW/MID-LEVEL FLOW FIELDS...SHEAR ASSOCIATED WITH 30+ KT
SOUTHWESTERLY 500 MB FLOW MAY BE ENOUGH TO ENHANCE THE RISK FOR
HAIL/GUSTY WINDS IN STRONGER STORMS.
...N CNTRL HIGH PLAINS INTO UPR PORTIONS OF THE MID MS VALLEY...
BENEATH NORTHWESTERLY MID-LEVEL FLOW ON THE SOUTHWESTERN PERIPHERY
OF THE AMPLIFYING UPPER TROUGH...MODELS ARE SUGGESTIVE OF POTENTIAL
FOR AT LEAST ONE OR TWO SMALL ORGANIZED STORM CLUSTERS LATE FRIDAY
AFTERNOON/NIGHT. WEAK TO MODERATE DESTABILIZATION IS EXPECTED TO
DEVELOP WITHIN A PRE-FRONTAL LOWER/MID TROPOSPHERIC THERMAL RIDGE
EXTENDING EAST SOUTHEASTWARD OUT OF THE NORTH CENTRAL ROCKIES INTO
THE MIDDLE MISSISSIPPI VALLEY. FORCING ASSOCIATED WITH WARM
ADVECTION ON THE NOSE OF THIS RIDGE COULD INITIATE STORM DEVELOPMENT
ACROSS SOUTHEAST IOWA/NORTHEAST MISSOURI/WEST CENTRAL
ILLINOIS...WHILE NOCTURNAL SOUTHERLY BOUNDARY LAYER JET DEVELOPMENT
COULD ENHANCE STORMS WITHIN...OR SPREADING OFF THE HIGHER TERRAIN
INTO...THE NORTH CENTRAL PLAINS. HOWEVER...THE SPREAD AMONG THE
NCEP SREF AND DETERMINISTIC MODELS CONCERNING THIS POTENTIAL REMAINS
RATHER LARGE...AND THIS IS REFLECTED IN THE LOW SEVERE PROBABILITIES
AT THE PRESENT TIME.
..KERR.. 05/28/2009
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