SWODY2
SPC AC 180536
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT SUN SEP 18 2011
VALID 191200Z - 201200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODEL GUIDANCE IS IN REASONABLE AGREEMENT INDICATING FULL-LATITUDE
UPPER TROUGH CURRENTLY OVER THE HIGH PLAINS WILL MOVE SLOWLY EWD AND
GRADUALLY WEAKEN AS IT MOVES ACROSS THE MS VALLEY AND GREAT LAKES
REGIONS. A STRONGER MORE COMPACT UPPER TROUGH IS FORECAST TO
AMPLIFY AS IT MOVES ACROSS MT AND THE DAKOTAS.
AT THE SURFACE...A LOW WILL MOVE ACROSS THE GREAT LAKES AS A
TRAILING COLD FRONT EXTENDING SWWD FROM THE LOW MOVES ACROSS THE
GREAT LAKES/OH VALLEY/MID SOUTH AND SERN TX. A SECOND SURFACE LOW
IS EXPECTED TO CONSOLIDATE AND DEEPEN OVER ND DURING THE SECOND HALF
OF THE PERIOD...AS A STRONG COLD FRONT ACCELERATES EWD/SEWD ACROSS
THE NRN PARTS OF THE ROCKIES AND PLAINS.
...SERN MT INTO SRN ND/NRN SD...
A STRONGLY DYNAMIC UPPER TROUGH AND ASSOCIATED DIGGING MID/UPPER
LEVEL JET STREAK IS FORECAST TO MOVE FROM MT INTO THE DAKOTAS DURING
THE PERIOD. INTENSE DPVA AND UPPER LEVEL DIVERGENCE WITHIN THE LEFT
EXIT REGION OF THE JET STREAK COUPLED WITH STRONG LOW LEVEL
CONVERGENCE ALONG THE COLD FRONT WILL PROVIDE FOCUSED ASCENT WITHIN
A MARGINALLY UNSTABLE ENVIRONMENT /MAXIMUM SBCAPE OF 250-500 J PER
KG/. MODEL FORECAST SOUNDINGS EXHIBIT STEEP LOW LEVEL LAPSE RATES
WITHIN A WELL-MIXED PBL ALONG AND IMMEDIATELY IN THE WAKE OF THE
COLD FRONT...WHERE LOW-TOPPED CONVECTION IS MOST LIKELY TO DEVELOP.
THUNDERSTORMS MAY ENHANCE THE POTENTIAL FOR DOWNWARD TRANSFER OF
STRONG LOW/MID LEVEL WIND FIELDS BEHIND THE FRONT...WITH
STRONG/ISOLATED SEVERE WIND GUSTS POSSIBLE. THE PRIMARY WIND THREAT
IS EXPECTED TO DEVELOP OVER PARTS OF SERN MT DURING THE LATE
AFTERNOON/EVENING AND SPREAD EWD INTO PARTS OF THE DAKOTAS AT NIGHT.
MINIMAL INSTABILITY IS EXPECTED TO PRECLUDE A GREATER SEVERE THREAT
ATTM.
...OH VALLEY ACROSS THE LOWER MS VALLEY REGION...
WIDESPREAD CONVECTION IS EXPECTED TO BE ONGOING NEAR THE EWD MOVING
COLD FRONT WITH EXTENSIVE CLOUDS/PRECIPITATION LIKELY TO INHIBIT
DIABATIC HEATING AND SUBSEQUENT DESTABILIZATION. BREAKS IN THE
CLOUD COVER MAY DEVELOP OVER LOCALIZED AREAS WHERE MLCAPE MAY
INCREASE TO 1000-1500 J/KG...HOWEVER MODEST LAPSE RATES WITHIN A
MOIST ENVIRONMENT SHOULD LIMIT OVERALL UPDRAFT INTENSITY. ISOLATED
STRONG STORMS MAY OCCUR BUT WEAK FLOW ALOFT AND MINIMAL VERTICAL
SHEAR ARE EXPECTED TO LIMIT OVERALL SEVERE THREAT.
..WEISS.. 09/18/2011
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