ACUS02 KWNS 300548
SWODY2
SPC AC 300545
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1245 AM CDT TUE SEP 30 2008
VALID 011200Z - 021200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
DOWNSTREAM OF A STRONG ZONAL JET NOSING ACROSS THE MID LATITUDE
PACIFIC...MODELS CONTINUE TO SUGGEST THAT THE CLOSED LOW WITHIN THE
SOUTHERN PORTION OF THE AMPLIFIED EASTERN PACIFIC TROUGH WILL
ACCELERATE NORTHEASTWARD WEDNESDAY. THE CIRCULATION IS PROGGED TO
DEFORM INTO AN INCREASINGLY SHEARED UPPER TROUGH APPROACHING THE
BRITISH COLUMBIA/PACIFIC NORTHWEST COAST BY 12Z THURSDAY...
CONTRIBUTING TO WEAKENING OF THE LARGE SCALE RIDGE OVER THE
INTERMOUNTAIN WEST AND U.S. ROCKIES. BUT...SHORT WAVE RIDGING IS
EXPECTED TO REMAIN STRONG TO THE LEE OF THE CANADIAN ROCKIES...AND
THE DOWNSTREAM LARGE-SCALE TROUGH AMPLIFIED ACROSS MUCH OF EASTERN
NORTH AMERICA.
WITHIN THE SHARP CYCLONIC FLOW REGIME IN THE EAST...MODEL GUIDANCE
HAS EXHIBITED CONSIDERABLE SPREAD CONCERNING SMALLER SCALE
FEATURES...INCLUDING AN INITIAL CLOSED LOW EXPECTED OVER THE GREAT
LAKES EARLY IN THE PERIOD...AND AT LEAST A COUPLE OF ASSOCIATED
SHORT WAVE IMPULSES...ONE PIVOTING AROUND ITS NORTHEASTERN
PERIPHERY...ANOTHER AROUND ITS SOUTHWESTERN/SOUTHERN PERIPHERY. IN
CONJUNCTION WITH THIS UNCERTAINTY...THE TIMING OF THE ADVANCEMENT OF
THE ASSOCIATED SURFACE COLD FRONT ACROSS ATLANTIC COASTAL AREAS IS
STILL UNCLEAR...AS IS THE EXTENT OF THE CONVECTIVE POTENTIAL.
...SRN MID ATLANTIC COAST INTO SOUTHERN NEW ENGLAND...
LATEST MODEL GUIDANCE APPEARS SUGGESTIVE OF AT LEAST A SLIGHTLY
SLOWER FRONTAL PASSAGE THAN EARLIER EXPECTED ACROSS COASTAL AREAS
WEDNESDAY. IF THIS OCCURS...OPPORTUNITY FOR MORE SIGNIFICANT
BOUNDARY LAYER DESTABILIZATION WILL BE GREATER...PARTICULARLY ALONG
A PRE-FRONTAL SURFACE TROUGH ACROSS PARTS OF EASTERN NORTH CAROLINA
INTO THE SOUTHERN DELMARVA.
FARTHER NORTH...NEAR A POSSIBLE WEAK FRONTAL WAVE ADVANCING ACROSS
NORTHERN MID ATLANTIC COASTAL AREAS INTO SOUTHERN NEW
ENGLAND...CLOUD COVER PROBABLY WILL BE A LIMITING FACTOR WITH REGARD
TO DESTABILIZATION. BUT...MID LEVEL FORCING/SHEAR IN THE EXIT
REGION OF A 50-70 KT 500 MB JET STREAK NOSING ACROSS THE MID
ATLANTIC COAST STATES WILL PROVIDE AT LEAST LOW POTENTIAL FOR
ISOLATED STRONG/SEVERE CONVECTIVE DEVELOPMENT.
POTENTIAL FOR MID/HIGH LEVEL SUBSIDENCE PRIOR TO THE FRONTAL PASSAGE
ACROSS SOUTHERN MID ATLANTIC COASTAL AREAS IS STILL A CONCERN.
BUT...GIVEN CURRENT MODEL FORECASTS OF POSSIBLE 1000- 2000 J/KG
MIXED LAYER CAPE...IF FORCING FOR UPWARD VERTICAL MOTION DEVELOPS
EARLIER THAN CURRENTLY SEEMS MOST PROBABLE... DEEP LAYER SHEAR WILL
BE SUFFICIENT FOR SEVERE STORMS CAPABLE OF PRODUCING LARGE
HAIL/DAMAGING WIND GUSTS. A NARROW LINE OF STORMS COULD FORM ACROSS
EASTERN NORTH CAROLINA COASTAL AREAS AND THE OUTER BANKS BEFORE
ADVANCING OFFSHORE WEDNESDAY AFTERNOON.
...NORTHERN INTERMOUNTAIN REGION INTO CENTRAL ROCKIES...
THE LARGE-SCALE PATTERN...COUPLED WITH OROGRAPHY...WILL SUPPORT
CONVECTIVE POTENTIAL WEDNESDAY OVER A FAIRLY BROAD AREA. BUT... THE
COVERAGE OF STORM DEVELOPMENT SHOULD REMAIN SPARSE DUE TO LIMITED
MOISTURE.
..KERR.. 09/30/2008
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