DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180557
SWODY1
SPC AC 180556

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT TUE SEP 18 2012

VALID 181200Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE ERN U.S. FROM
CENTRAL AND ERN NY/SRN NEW ENGLAND SSWWD ACROSS THE CAROLINAS...

...SYNOPSIS...
AN EXPANSIVE/HIGH-AMPLITUDE UPPER TROUGH WILL PROGRESS SLOWLY EWD
ACROSS THE ERN U.S. THIS PERIOD...AS A WEAKER SERN U.S. SYSTEM
BECOMES ABSORBED WITHIN THE LARGER-SCALE CYCLONIC FLOW.
MEANWHILE...A LARGE RIDGE WILL PREVAIL ACROSS THE ROCKIES/WRN CONUS.


AT THE SURFACE...A COLD FRONT ASSOCIATED WITH THE UPPER TROUGH IS
EXPECTED TO CROSS THE APPALACHIANS EARLY...STRETCHING FROM ERN NY
SSWWD ACROSS THE ATLANTIC COAST STATES BY SUNSET AND REACHING THE
ATLANTIC COAST LATE IN THE PERIOD. WIDESPREAD CONVECTION NEAR AND
AHEAD OF THIS FRONT WILL POSE A RISK FOR SEVERE WEATHER --
PARTICULARLY FROM NY/SRN NEW ENGLAND SWD ACROSS THE CAROLINAS.

...ERN U.S. ALONG AND E OF THE APPALACHIANS...
A VERY COMPLEX SCENARIO IS UNFOLDING...WITH WIDESPREAD PRECIPITATION
EXPECTED TO BE ONGOING AT THE START OF THE PERIOD WITHIN A BEND FROM
NEW YORK SWWD INTO THE CENTRAL GULF COAST REGION -- LARGELY
ASSOCIATED WITH THE WEAKENING/SRN UPPER SYSTEM. THIS WIDESPREAD
CLOUDINESS/PRECIPITATION WILL RESULT IN WEAK LAPSE RATES...AND
LITTLE POTENTIAL FOR APPRECIABLE AIRMASS DESTABILIZATION ACROSS A
LARGE PORTION OF THE RISK AREA.

HOWEVER...AS THE MAIN UPPER TROUGH EXPANDS/SHIFTS EWD WITH
TIME...STRONG FLOW ALOFT E OF THE TROUGH WILL SPREAD ACROSS THE WARM
SECTOR...RESULTING IN SHEAR PROFILES HIGHLY SUPPORTIVE OF ROTATING
STORMS. CLEARLY...THE LACK OF BUOYANCY ACROSS MANY AREAS WILL ACT
TO LIMIT SEVERE POTENTIAL...BUT THE DEGREE OF VEERING/SHEAR
ANTICIPATED WARRANTS LOW SEVERE/TORNADO PROBABILITY ACROSS THE
MAJORITY OF THE U.S. E OF THE APPALACHIAN CREST.

ATTM...IT APPEARS THAT THE GREATEST SEVERE THREAT MAY EVOLVE ACROSS
PARTS OF SERN NY/ERN PA/MD/VA AND INTO SRN NEW ENGLAND/NJ/DE. THIS
PORTION OF THE REGION MAY REMAIN E OF THE MORE EXPANSIVE ZONE OF
CLOUDS/PRECIPITATION INTO THE AFTERNOON -- POSSIBLY ALLOWING POCKETS
OF WEAK HEATING/DESTABILIZATION. THUS -- WITH SOME POSSIBILITY OF
GREATER THERMODYNAMIC SUPPORT FOR MORE VIGOROUS CONVECTION IN THIS
AREA...POTENTIAL FOR UPDRAFTS TO INTERACT WITH A VERY FAVORABLE
BACKGROUND KINEMATIC FIELD SUGGESTS POTENTIAL FOR MORE WIDESPREAD
DAMAGING WINDS AND A FEW TORNADOES.

GIVEN UNCERTAINTY...AND A GENERAL LACK OF CAPE ANTICIPATED
ATTM...THIS SCENARIO DOES NOT APPEAR TO WARRANT MDT RISK UPGRADE
ATTM. STILL...SMALL ZONES OF FAIRLY INTENSE/ROTATING CONVECTION
CAPABLE OF PRODUCING LOCALLY DAMAGING SEVERE WEATHER APPEAR LIKELY.


SEVERE THREAT SHOULD CONTINUE INTO THE EVENING/OVERNIGHT HOURS AS
STRONG SHEAR PERSISTS -- PARTICULARLY ACROSS THE NRN HALF OF THE
RISK AREA...ENDING FROM W TO E AS THE FRONT GRADUALLY
APPROACHES/REACHES THE COAST.

..GOSS/SMITH.. 09/18/2012

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