SWODY2
SPC AC 131729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT TUE SEP 13 2011
VALID 141200Z - 151200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
SPLIT FLOW UPPER PATTERN WILL PREVAIL THROUGH WEDNESDAY. NRN STREAM
WILL REMAIN DOMINATED BY A BROAD UPPER LOW CENTERED OVER THE HUDSON
BAY AREA. SEVERAL VORTICITY MAXIMA WILL ROTATE THROUGH THIS FEATURE
INCLUDING A SIGNIFICANT SHORTWAVE TROUGH THAT WILL MOVE SEWD INTO
THE GREAT LAKES REGION ACCOMPANIED BY A STRONG CP FRONT. THE FRONT
SHOULD EXTEND FROM A SURFACE LOW IN ONTARIO SWWD INTO THE CNTRL
PLAINS EARLY WEDNESDAY...SURGING SWD INTO THE SRN PLAINS AND LOWER
MS VALLEY BY EVENING. A SLOW MOVING UPPER LOW WILL PERSIST OVER THE
SWRN STATES WITHIN THE SRN STREAM. VORTICITY MAXIMUM LOCATED OVER
NRN NM IS FORECAST TO EJECT THROUGH KS/OK AND INTO THE LOWER MS AND
TN VALLEY WEDNESDAY.
...LOWER MS AND TN VALLEY AREA...
AN AXIS OF MID 60S BOUNDARY LAYER DEWPOINTS WILL PERSIST WEST OF
RETREATING SURFACE RIDGE IN THE PRE-FRONTAL WARM SECTOR FROM THE
LOWER MS VALLEY INTO WRN PORTIONS OF TN VALLEY. A NARROW PLUME OF
STEEPER 6.5-7 C/KM MID LEVEL LAPSE RATES WILL ADVECT EWD ABOVE THE
MOIST AXIS...RESULTING IN MODERATE INSTABILITY AS DIABATIC HEATING
COMMENCES. MODELS INDICATE ELEVATED STORMS WILL BE IN PROGRESS AT
START OF THE PERIOD WITHIN ZONE OF DEEPER POST FRONTAL ISENTROPIC
ASCENT. BOUNDARY LAYER DESTABILIZATION AND WEAKENING CAP SHOULD
PROMOTE THE DEVELOPMENT OF SURFACE BASED STORMS ALONG THE FRONT BY
AFTERNOON. EFFECTIVE SHEAR MAY INCREASE TO 35-40 KT IN ASSOCIATION
WITH PROGRESSIVE SRN STREAM IMPULSE AND AMPLIFYING NRN STREAM
TROUGH. A FEW STORMS MAY BECOME CAPABLE OF PRODUCING ISOLATED
DAMAGING WIND AND LARGE HAIL THROUGH EARLY EVENING. A PORTION OF
THIS AREA MIGHT NEED TO BE INCLUDED IN A SLIGHT RISK IN THE DAY 1
UPDATES.
...SRN PLAINS...
SCATTERED TSTMS WILL ACCOMPANY THE SOUTHWARD-MOVING COLD FRONT AND
ASSOCIATED POST-FRONTAL HIGH PLAINS UPSLOPE REGIME ACROSS PORTIONS
OF NM AND THE OK/TX PANHANDLES. FLOW ALOFT WILL REMAIN MODEST WITH
WEAK SHORTWAVE RIDGING...BUT SUFFICIENT DIRECTIONAL SHEAR WILL EXIST
NORTH OF FRONT TO SUPPORT 30-40 KT EFFECTIVE SHEAR. IT IS NOT
ENTIRELY CLEAR WHAT DEGREE OF DESTABILIZATION WILL OCCUR...BUT
STRONG HEATING ALONG/SOUTH OF THE FRONT AND A NEAR-FRONTAL CORRIDOR
OF MODEST DESTABILIZATION /UP TO 1000-1500 J PER KG SBCAPE/...ALONG
WITH SUFFICIENT VERTICAL SHEAR...MAY YIELD ISOLATED/EPISODIC SEVERE
WIND AND/OR HAIL WITH THE MORE ROBUST/SUSTAINED STORMS WEDNESDAY
AFTERNOON/EVENING.
...MID ATLANTIC...
A FEW STORMS MAY DEVELOP OVER THE HIGHER TERRAIN OF THE CNTRL
APPALACHIANS AREA WHERE THE ATMOSPHERE SHOULD BECOME MODERATELY
UNSTABLE WITH 1500 J/KG MLCAPE. WEAK VERTICAL SHEAR WILL SUPPORT
MULTICELL STORMS...BUT THE THERMODYNAMIC ENVIRONMENT WITH STEEPENING
LOW LEVEL LAPSE RATES MAY BECOME AT LEAST MARGINALLY SUPPORTIVE OF
ISOLATED STRONG WIND GUSTS DURING THE AFTERNOON.
..DIAL.. 09/13/2011
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