SWODY2
SPC AC 181720
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1220 PM CDT SUN SEP 18 2011
VALID 191200Z - 201200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODEL GUIDANCE REMAINS IN AGREEMENT INDICATING THE FULL-LATITUDE
UPPER TROUGH CURRENTLY MOVING OVER THE CENTRAL U.S. WILL GRADUALLY
WEAKEN AS IT PROGRESSES E OF THE MS VALLEY REGION ON MONDAY.
MEANWHILE...A STRONGER MORE COMPACT UPPER TROUGH IS FORECAST TO
AMPLIFY AS IT TRACKS ESEWD ACROSS MT INTO THE NRN PLAINS ON
MONDAY/MONDAY NIGHT.
AT THE SURFACE...A LOW WILL MOVE ACROSS THE GREAT LAKES AS A
TRAILING COLD FRONT EXTENDING SWWD FROM THE LOW UNDERGOES
FRONTOLYSIS...ADVANCING ACROSS THE GREAT LAKES/OH VALLEY/MID SOUTH
AND SERN TX. A SECOND SURFACE LOW IS EXPECTED TO CONSOLIDATE AND
DEEPEN OVER SRN MANITOBA/ND DURING THE SECOND HALF OF THE PERIOD...
AS A STRONG COLD FRONT ACCELERATES EWD/SEWD FROM NRN PARTS OF THE
ROCKIES TO THE NRN AND CENTRAL PLAINS.
...SERN MT INTO SRN ND/NRN SD...
A STRONGLY DYNAMIC UPPER TROUGH AND ASSOCIATED DIGGING MID/UPPER
LEVEL JET STREAK ARE 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.
MODELS MAINTAIN THESE SYNOPTIC/MESOSCALE FORECAST DETAILS WITH THE
POTENTIAL FOR TSTMS TO ENHANCE THE DOWNWARD TRANSFER OF STRONG
LOW/MID LEVEL WIND FIELDS BEHIND THE FRONT...SUCH THAT STRONG/
ISOLATED SEVERE WIND GUSTS ARE 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 WILL PRECLUDE A GREATER SEVERE THREAT...AND THUS THIS
OUTLOOK WILL MAINTAIN LOW SEVERE PROBABILITIES PRIMARILY FOR AN
ISOLATED SEVERE WIND GUST THREAT.
...OH VALLEY INTO 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 COULD
INCREASE TO 1000-1500 J/KG. HOWEVER...MODEST LAPSE RATES WITHIN A
MOIST ENVIRONMENT SHOULD LIMIT OVERALL UPDRAFT INTENSITIES.
ISOLATED STRONG STORMS MAY OCCUR BUT WEAKENING FLOW ALOFT AND
MINIMAL VERTICAL SHEAR ARE EXPECTED TO LIMIT OVERALL SEVERE THREAT.
..PETERS.. 09/18/2011
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