Wednesday, January 11, 2012

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 111301
SWODY1
SPC AC 111259

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0659 AM CST WED JAN 11 2012

VALID 111300Z - 121200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...

INTENSE MID- AND UPPER-LEVEL LOW OVER THE LOWER MS VALLEY WILL
GRADUALLY WEAKEN THROUGH THE D1 PERIOD WHILE LIFTING NEWD INTO THE
MID ATLANTIC STATES TONIGHT. DESPITE THE DE-AMPLIFICATION OF THIS
SYSTEM WITH TIME...IT WILL BE ATTENDED BY 12-HR HEIGHT FALLS AT 500
MB OF 100-150 M AND A 50-70 KT MIDLEVEL JET STREAK. IN THE LOW
LEVELS...THE PRIMARY SURFACE CYCLONE IS EXPECTED TO DEVELOP FROM
MIDDLE TN INTO CNTRL/ERN KY BY AFTERNOON...EVENTUALLY REACHING LAKE
ERIE BY 12/12Z. AS THE STRONGER DEEP-LAYER FORCING FOR ASCENT
BEGINS TO SPREAD ACROSS THE CNTRL/SRN APPALACHIANS LATER
TODAY...SECONDARY CYCLONE DEVELOPMENT WILL OCCUR OVER UPSTATE SC
WITH THIS FEATURE TRACKING NEWD INTO THE DELMARVA LATE TONIGHT INTO
THURSDAY MORNING. MEANWHILE...THE TRAILING COLD FRONT WILL CONTINUE
EWD THROUGH THE SERN AND MID ATLANTIC STATES...INCLUDING FL BY THE
END OF THE D1 PERIOD.

...GA NEWD THROUGH THE CAROLINAS AND SERN VA...

CURRENT SURFACE OBSERVATIONS INDICATE THAT A WEDGE OF HIGHER THETA-E
AIR /I.E. DEWPOINTS IN THE LOW-MID 60S/ EMANATING FROM THE NERN
G.O.M. IS RAPIDLY NARROWING OWING TO THE EWD PROGRESSION OF COLD
FRONT AND PRE-FRONTAL CONVECTIVE BAND. WHILE MOISTURE FLUX OFF THE
GULF STREAM WILL INCREASE TODAY IN RESPONSE TO THE DEVELOPMENT OF A
40-50 KT LLJ...EXPECT BOUNDARY LAYER DEWPOINTS TO REMAIN IN THE
UPPER 50S TO LOWER 60S. WHEN COUPLED WITH WEAK LOW- TO MIDLEVEL
LAPSE RATES...THERMODYNAMIC ENVIRONMENT WILL BECOME ONLY MARGINALLY
UNSTABLE WITH MLCAPE REMAINING BELOW 500 J/KG AT MOST LOCATIONS.

WHILE ISOLATED SEVERE STORMS WILL BE POSSIBLE TODAY AHEAD OF
MIGRATORY MIDLEVEL SYSTEM AND ASSOCIATED SURFACE COLD FRONT...THE
WEAK INSTABILITY IS EXPECTED TO LIMIT THE POTENTIAL FOR A MORE
ROBUST SEVERE WEATHER THREAT. THE EXCEPTION MAY BE OVER ERN NC INTO
FAR SERN VA LATER TODAY INTO TONIGHT. HERE...SLIGHTLY HIGHER
MOISTURE CONTENT /AND RESULTANT INSTABILITY/ WILL COINCIDE WITH A
STRONG LOW- AND DEEP-LAYER SHEAR AND INCREASED ISALLOBARIC FORCING
ALONG AND SE OF SECONDARY SURFACE LOW. AS SUCH...A COMPARATIVELY
GREATER RISK FOR SUPERCELLS AND/OR BOWING STRUCTURES WILL EXIST.
THIS AREA WILL CONTINUE TO BE MONITORED FOR A POSSIBLE UPGRADE TO
SLIGHT RISK IN LATER OUTLOOKS.

...FL...

PRE-FRONTAL CLUSTERS OF TSTMS ONGOING OVER THE ERN G.O.M. ARE
EXPECTED TO MOVE ONSHORE TODAY AHEAD OF COLD FRONT. HERE TOO...POOR
MIDLEVEL LAPSE RATES WILL LIMIT THE DEGREE OF INSTABILITY...THOUGH
BOUNDARY LAYER DEWPOINTS IN THE LOW-MID 60S AND BREAKS IN THE CLOUDS
WILL YIELD MLCAPE OF 500-700 J/KG. GIVEN THE PRESENCE OF 40-45 KT
OF DEEP...WLY SHEAR AND MODESTLY STRONG LOW-LEVEL SHEAR...A LOW
PROBABILITY RISK FOR DAMAGING WINDS AND PERHAPS A TORNADO WILL EXIST
THIS AFTERNOON.

...MIDDLE TN INTO SRN APPALACHIANS...

ISOLATED OCCURRENCES OF HAIL APPROACHING SEVERE LEVELS WILL BE
POSSIBLE TODAY WITH STORMS FORMING INVOF MIDLEVEL COLD CORE.

..MEAD/BOTHWELL.. 01/11/2012

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