DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 220543
SWODY1
SPC AC 220541

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1141 PM CST WED NOV 21 2012

VALID 221200Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
IN THE MID/UPPER LEVELS...A STRONG SHORTWAVE TROUGH WILL PROGRESS
EWD FROM THE NRN PLAINS TO THE WRN GREAT LAKES WHILE AMPLIFYING. A
DISORGANIZED CLUSTER OF VORTICITY MAXIMA WILL BE ADVECTED NEWD FROM
THE SRN PLAINS TO THE ERN GREAT LAKES IN ADVANCE OF THE SHORTWAVE
TROUGH. TO THE E OF THESE FEATURES...A RIDGE AXIS WILL SHIFT EWD
TOWARD THE E COAST THROUGH THE PERIOD WHILE A CYCLONE MOVES ENEWD
OVER THE ATLANTIC WATERS OFF THE MID ATLANTIC/SERN U.S. COAST.

AT THE SFC...AN EXTENSIVE COLD FRONT ACCOMPANYING THE STRONG
SHORTWAVE TROUGH WILL TRACK EWD/SWD ACROSS PARTS OF THE CNTRL U.S.
AND LIE FROM THE LOWER GREAT LAKES TO THE SRN PLAINS BY EARLY FRI
MORNING. ANTICYCLONIC FLOW OVER MUCH OF THE GULF OF MEXICO...
COMBINED WITH DEEP/SUBSIDENT NWLY/NLY FLOW BETWEEN THE ERN U.S.
RIDGE AXIS AND THE WRN ATLANTIC CYCLONE...WILL LARGELY HINDER
BOUNDARY-LAYER MOISTURE RETURN IN ADVANCE OF THE FRONT.

...MID MS VALLEY TO THE GREAT LAKES THIS AFTERNOON AND TONIGHT...
MEAGER LOW-LEVEL MOISTURE WITH SFC DEWPOINTS FROM THE 40S TO THE
LOWER 50S WILL CHARACTERIZE A NARROW ZONE LEADING THE FRONT. WITHIN
THIS ZONE...FORECAST SOUNDINGS SUGGEST THAT VERY LITTLE...IF
ANY...SURFACE-BASED INSTABILITY WILL DEVELOP...WITH AROUND
100-800 J/KG OF ELEVATED CAPE FOR PARCELS LIFTED WITHIN THE
850-750-MB LAYER. HOWEVER...INTENSE LARGE-SCALE ASCENT ACCOMPANYING
THE SHORTWAVE TROUGH...WITH 500-MB HEIGHT FALLS FROM 100 TO OVER 200
GEOPOTENTIAL METERS PER 12 HOURS...COUPLED WITH THE DEEP FRONTAL
CIRCULATION...MAY PROMOTE THE DEVELOPMENT OF LOW-TOPPED CONVECTIVE
BANDS WITH INFREQUENT LIGHTNING INVOF THE FRONT.

THE STRENGTH OF THE SYNOPTIC-SCALE ASCENT AND DEEP SHEAR...ALONG
WITH A 40-50-KT 925-850-MB JET MAXIMUM OVERLAYING THE ELEVATED WARM
SECTOR...OFFER SOME CONCERN THAT THE CONVECTIVE BANDS MAY PRODUCE
STRONG TO POTENTIALLY ISOLATED INSTANCES OF SVR WIND GUSTS. THE
STRONG/SVR-WIND THREAT MAY ALSO BE ENHANCED BY MODEST
TEMPERATURE-DEWPOINT SPREADS NEAR THE SFC DURING THE AFTERNOON. THE
AREA OF GREATEST CONCERN FOR THESE CONVECTIVE WINDS LIES FROM CNTRL
MO NEWD TO SRN LOWER MI.

HOWEVER...WITH FORECAST SOUNDINGS DEPICTING STRONG BOUNDARY-LAYER
STABILITY -- INCLUDING ONE OR MORE LOW-LEVEL INVERSION LAYERS --
BENEATH THE ELEVATED CAPE LAYER...THERE IS LARGE UNCERTAINTY IN THE
POTENTIAL FOR THE STRONG FLOW ALOFT TO BECOME MANIFESTED AT THE SFC
AS SVR WIND GUSTS. CLOUDINESS AND SHOWERS IN ASSOCIATION WITH ASCENT
ACCOMPANYING THE CLUSTER OF VORTICITY MAXIMA MAY FURTHER MITIGATE
ANY PRE-FRONTAL DESTABILIZATION ALONG WITH ANY SVR THREAT.
ACCORDINGLY...SVR-WIND PROBABILITIES HAVE NOT BEEN INTRODUCED
ATTM...BUT MAY EVENTUALLY BE NEEDED IF DESTABILIZATION BECOMES A
GREATER CONCERN AHEAD OF THE FRONT.

...SRN PLAINS TO WRN PARTS OF THE LOWER MS VALLEY THIS AFTERNOON AND
TONIGHT...
MODESTLY RICHER MOISTURE WITHIN A PARTIALLY MODIFIED AIR MASS WILL
BE FOUND AHEAD OF THE SRN EXTENT OF THE FRONT...WITH SFC DEWPOINTS
INTO THE MIDDLE 50S ASSOCIATED WITH RELATIVELY GREATER
INSTABILITY -- ALBEIT LIMITED. HOWEVER...WITH THE STRONGER DEEP
FLOW / FORCING FOR ASCENT BEING FOCUSED FARTHER NORTH IN CLOSER
PROXIMITY TO THE STRONG SHORTWAVE TROUGH...ORGANIZED/SVR CONVECTION
WILL BE UNLIKELY. STORMS MAY ALSO HAVE A TENDENCY TO BECOME UNDERCUT
BY THE SEWD/SWD-SURGING FRONT...LIMITING CONVECTIVE INTENSITY.

..COHEN/DARROW.. 11/22/2012

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