SWODY1
SPC AC 201941
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0241 PM CDT THU SEP 20 2007
VALID 202000Z - 211200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE NRN
PLAINS TO THE UPR MS VLY...
..NRN PLAINS TO THE UPR MS VLY...
MID-AFTN SFC ANALYSIS PLACED A 1004 MB LOW S OF KBIS WITH A
LEE-TROUGH SWD INTO NCNTRL NEB AND NWD INTO SERN SASK. ONGOING
ELEVATED TSTM CLUSTERS CONTINUE TO ENHANCE A BAROCLINIC ZONE SEWD
FROM THE LOW ACROSS NERN SD AND SRN MN.
REGIONAL VWPS/PROFILERS CONFIRM EARLIER GUIDANCE IN SHIFTING THE 50
KT SWLY LOW-LEVEL JET NEWD WITH TIME THIS AFTN. STG-SVR ELEVATED
TSTM CLUSTERS THAT HAVE AFFECTED CNTRL MN MOST OF THE DAY HAVE BEEN
WEAKENING AND SHIFTING NEWD IN TANDEM WITH THIS JET. ADDITIONAL
ELEVATED STORMS WILL REMAIN POSSIBLE THROUGH THE EVENING ALONG THE
SWRN FLANK OF THE MCS AS THE ENHANCED SWLY LOW-LEVEL FLOW IMPINGES
ON THE BAROCLINIC ZONE WITH THE THREAT FOR LARGE HAIL AND PERHAPS
GUSTY WINDS.
SOUTH OF THE FRONT...AIRMASS HAS HEATED CONSIDERABLY OWING TO AMPLE
INSOLATION AND MOIST BOUNDARY LAYER. THE 18Z ABR SOUNDING...
HOWEVER...SAMPLED A STOUT EML /CINH OF 138 J/KG/. ABSENCE OF
MEANINGFUL LARGE SCALE FORCING IN WAKE OF THE MORNING MID-LEVEL WAVE
SUGGESTS THAT HEATING AND CONVERGENCE ALONG THE FRONT WILL BE NEEDED
TO INITIATE SFC-BASED STORMS /CONVECTIVE TEMPERATURE OF 94 DEG F/.
GIVEN STRENGTH OF THE EML AND THE WARM TEMPERATURES
NEEDED...UNCERTAINTY HAS NOT DECREASED WITH RESPECT TO SFC-BASED
INITIATION. NONETHELESS...GUIDANCE...ESPECIALLY THE RUC/WRF...
CONTINUE TO SUGGEST THE POTENTIAL FOR SFC-BASED STORMS AND THIS OTLK
WILL REFLECT CONDITIONAL SVR PROBABILITIES. RECENT DEVELOPMENT
NEAR/NORTH OF WOOD LAKE MN CLOSER TO THE FRONT MAY BE SIGNS THAT
EARLIER GUIDANCE WILL NOT BE TOTALLY OFF-BASE. GIVEN A STORM...THE
VERTICAL SHEAR AND STEEP LAPSE RATES ENVIRONMENT WOULD SUPPORT
SUPERCELLS WITH VERY LARGE HAIL...DMGG WIND GUSTS AND ISOLD
TORNADOES.
OTHERWISE...STRONG MID-LEVEL WAVE DIGGING THROUGH ALBERTA WILL REACH
THE NRN PLAINS LATE TONIGHT. STRONG ASCENT WILL CONTRIBUTE TO A
SECONDARY ENHANCEMENT OF THE SLY LL-FLOW LATER TONIGHT AHEAD OF A
DEEPENING CYCLONE OVER ND. TSTMS SHOULD DEVELOP WITHIN THE WARM
ADVECTION REGIME WHERE LAPSE RATES ALOFT WILL REMAIN QUITE STEEP AND
BULK SHEAR STRONG. AS A RESULT...A FEW OF THESE STORMS MAY PRODUCE
LARGE HAIL AND DMGG WIND GUSTS ACROSS PARTS OF ND.
.RACY.. 09/20/2007
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