Saturday, October 25, 2008

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 250548
SWODY1
SPC AC 250545

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1245 AM CDT SAT OCT 25 2008

VALID 251200Z - 261200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
MODELS INDICATE THAT THE STRONG POLAR JET STREAK EMANATING FROM THE
PACIFIC WILL CONTINUE TO NOSE SOUTHEAST OF THE CANADIAN/NORTHERN
U.S. ROCKIES TODAY INTO EARLY SUNDAY. THIS IS PROGGED TO BE
ACCOMPANIED BY THE AMPLIFICATION OF A COLD UPPER TROUGH FROM THE
CENTRAL CANADIAN PROVINCES THROUGH THE UPPER MIDWEST AND MIDDLE
MISSISSIPPI/OHIO VALLEYS...WHICH WILL GRADUALLY OVERTAKE LINGERING
TROUGHING ASSOCIATED WITH THE CLOSED LOW NOW LIFTING INTO THE GREAT
LAKES REGION. AS AN UPPER RIDGE REMAINS STRONG OFF THE ATLANTIC
COAST...A SIGNIFICANT IMPULSE ASSOCIATED WITH THE REMNANTS OF THE
CLOSED LOW IS EXPECTED TO PIVOT ACROSS THE UPPER OHIO VALLEY AND
LOWER GREAT LAKES REGION INTO EASTERN CANADA...AROUND THE CENTER OF
A BROADER VORTEX DEVELOPING TO THE SOUTHWEST OF HUDSON BAY. AT THE
SAME TIME...ANOTHER IMPULSE DIGGING TO THE SOUTHEAST OF THE OZARK
PLATEAU WILL BECOME INCREASINGLY SHEARED AS IT APPROACHES SOUTH
ATLANTIC COASTAL AREAS LATE TONIGHT.

...MID ATLANTIC COAST STATES...
BOUNDARY LAYER MOISTENING IS EXPECTED TO ACCOMPANY A WEAK SURFACE
WAVE THROUGH PORTIONS OF THE CENTRAL/EASTERN CAROLINAS BY DAYBREAK.
THIS MAY CONTINUE NORTHWARD THROUGH PARTS OF EASTERN VIRGINIA AND
THE DELMARVA PENINSULA...EAST OF A DEVELOPING LEE SURFACE TROUGH.
BUT...MODELS SUGGEST THAT THE WAVE WILL WEAKEN EARLY IN THE PERIOD.
COUPLED WITH THE PROSPECT FOR CONSIDERABLE EARLY DAY CLOUD COVER
ACROSS MUCH OF THE REGION...FOLLOWED BY DRYING/WARMING ALOFT
ASSOCIATED WITH MID-LEVEL SUBSIDENCE... THERMODYNAMIC PROFILES ARE
NOT EXPECTED TO BE CONDUCIVE FOR VIGOROUS CONVECTIVE DEVELOPMENT
THROUGH MUCH OF THE DAY. HOWEVER...IT IS POSSIBLE THAT FORCING ON
THE TAIL END OF THE IMPULSE LIFTING THROUGH THE NORTHEAST COULD
BECOME SUFFICIENT FOR ISOLATED STORM DEVELOPMENT PRIOR TO A COLD
FRONTAL PASSAGE EARLY THIS EVENING. THE BEST CHANCE FOR THIS
APPEARS TO BE ACROSS PARTS OF NORTHEASTERN NORTH CAROLINA INTO
SOUTHEAST VIRGINIA...WHERE LINGERING INSTABILITY ASSOCIATED WITH
BETTER AFTERNOON SURFACE HEATING WILL EXIST IN THE PRESENCE OF
FAVORABLE DEEP LAYER SHEAR FOR SUPERCELLS.

...NORTHERN MID ATLANTIC COAST INTO HUDSON/CHAMPLAIN VALLEYS...
FORCING ALONG A COLD FRONT ASSOCIATED WITH THE SHORT WAVE IMPULSE
LIFTING INTO EASTERN CANADA MAY BE SUFFICIENT TO SUPPORT A NARROW
CONVECTIVE LINE...WITHIN A BROADER PRECIPITATION SHIELD...ACROSS THE
REGION DURING THE LATE AFTERNOON INTO EARLY EVENING HOURS. WITH
SOUNDINGS EXPECTED TO BE CHARACTERIZED BY WEAKLY UNSTABLE TO STABLE
LAPSE RATES AND SATURATION THROUGH A DEEP LAYER OF THE LOWER/MID
TROPOSPHERE...CONVECTION SHOULD NOT BE PARTICULARLY VIGOROUS.
BUT...IT COULD CONTRIBUTE TO THE DOWNWARD MIXING OF MOMENTUM
ASSOCIATED WITH A 50-70+ KT SOUTHERLY 850 MB JET LIFTING
NORTHEASTWARD ACROSS THE REGION...AHEAD OF THE COLD FRONT. IF THIS
OCCURS...STRONG SURFACE GUSTS AND SPORADIC WIND DAMAGE COULD
ACCOMPANY THE LINE.

...NORTHERN PLAINS...
MODELS INDICATE WEAK DESTABILIZATION SUPPORTIVE OF SCATTERED LOW
TOPPED CONVECTIVE DEVELOPMENT IN THE EXIT REGION OF A STRONG
MID/UPPER JET STREAK PROGGED TO NOSE ACROSS PARTS OF EASTERN NORTH
DAKOTA INTO NORTHWEST MINNESOTA LATE THIS AFTERNOON. WHILE UPDRAFTS
LIKELY WILL BE WEAK...A FAIRLY DEEP MIXED BOUNDARY LAYER WITH
SIZABLE TEMPERATURE/DEW POINT SPREADS...COUPLED WITH 40+ KT FLOW
JUST OFF THE SURFACE...COULD PROMOTE A FEW STRONG WIND GUSTS
APPROACHING OF BRIEFLY EXCEEDING SEVERE LIMITS AT THE SURFACE.

..KERR/GRAMS.. 10/25/2008

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