SWODY1
SPC AC 050558
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT FRI OCT 05 2007
VALID 051200Z - 061200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS UPPER MIDWEST...
..SYNOPSIS...
DOMINANT UPPER AIR FEATURE FOR UPCOMING PERIOD WILL REMAIN
STRENGTHENING TROUGH OVER WRN CONUS...WITH OPERATIONAL SPECTRAL/WRF
AND MANY SREF MEMBERS PREDICTING CLOSED LOW OVER NV BY 6/00Z.
DOWNSTREAM...HEIGHTS GENERALLY ARE FCST TO RISE THROUGHOUT MOST OF
PERIOD ACROSS MID/UPPER MS VALLEY AND DAKOTAS...AS SYNOPTIC RIDGE
BUILDS DOWNSTREAM FROM DEEPENING WRN TROUGH.
SFC CYCLOGENESIS IS EXPECTED INVOF CENTRAL/NERN WY...WITH LEE
TROUGHING SSEWD ACROSS ERN CO. WARM FRONT WILL CONTINUE TO BECOME
BETTER DEFINED ACROSS NRN PLAINS...EXTENDING FROM WY LOW EWD ACROSS
SD AND SRN MN -- NEAR I-90 -- BETWEEN 6/00Z-6/06Z TIME FRAME.
..N-CENTRAL CONUS...
TWO PRIMARY EPISODES OF CONVECTION ARE MOST PROBABLE DURING PERIOD
IN THIS REGION...
1. MORNING PLUME CARRYING OVER FROM PREVIOUS PERIOD...AND MOVING
NEWD FROM NERN NEB/NWRN IA/SERN SD AREA ACROSS ERN MN/WRN WI. THIS
ACTIVITY MAY PRODUCE ISOLATED HAIL...SOME OF WHICH MAY REACH SVR
LIMITS. ENVIRONMENT SHOULD BE CHARACTERIZED BY 30-40 KT EFFECTIVE
BULK SHEAR...AND MRGLLY UNSTABLE MIDLEVEL LAPSE RATES SUPPORTING
500-1000 J/KG ELEVATED MUCAPE.
2. CONDITIONAL SLGT RISK FOR SVR ASSOCIATED WITH POTENTIAL FOR
AFTERNOON DEVELOPMENT ALONG OUTFLOW AND/OR DIFFERENTIAL HEATING
BOUNDARIES ASSOCIATED WITH MORNING ACTIVITY...ESPECIALLY INVOF ANY
INTERSECTION WITH SYNOPTIC WARM FRONT. STRONG LOW-LEVEL SHEAR IS
LIKELY ALONG THESE BOUNDARIES...WITH 35-45 KT 850 MB SSWLYS
SUPERIMPOSED ATOP BACKED SFC WINDS. FCST LOW LEVEL HODOGRAPHS
ACROSS CATEGORICAL SLGT RISK AREA YIELD 0-1 KM SRH TO NEAR 200
J/KG...0-3 KM SRH 300-400 J/KG...ALTHOUGH WEAKNESSES IN 3-6 KM AGL
FLOW WILL LIMIT DEEP LAYER SHEAR.
EXPECT STEEPENING LAPSE RATES ALOFT WITH WWD EXTENT...WHICH WILL
COMBINE WITH 60S/ISOLATED 70 F SFC DEW POINTS TO YIELD MLCAPES
1500-2000 J/KG. EXPECT PROGRESSIVELY MORE SBCINH INVOF WARM FRONT
WITH WWD EXTENT ALSO. NEGATIVE FACTORS INCLUDE POTENTIAL FOR
CAPPING TO SIGNIFICANTLY LIMIT OR MAYBE ELIMINATE DIURNAL
DEVELOPMENT...AND LACK OF SIGNIFICANT LARGE SCALE FORCING BENEATH
AMPLIFYING MID-UPPER RIDGE. ANY ACTIVITY THAT DOES DEVELOP BEFORE
DARK NEAR FRONT MAY PRODUCE DAMAGING GUSTS AND LARGE HAIL.
ADDITIONAL DEVELOPMENT MAY OCCUR AFTER DARK NEAR NOSE OF
STRENGTHENING LLJ....ACROSS ERN DAKOTAS/MN...WITH LARGE HAIL BEING
MAIN THREAT.
..W-CENTRAL/INTERMOUNTAIN...
CONDITIONAL DAMAGING WIND POTENTIAL EXISTS IN ELONGATED SWATH AHEAD
OF DEEP UPPER TROUGH...CORRESPONDING CLOSELY BOTH TO AXIS OF 50-75
KT 500 MB JET AND REASONABLY PROGGED CONVECTIVE PRECIP IN SEVERAL
MODELS. VERY FAST STORM MOTIONS ARE LIKELY GIVEN INTENSITY OF FCST
MID-UPPER WINDS. BUNKERS ET AL. ALGORITHM APPLIED TO PROGGED
HODOGRAPHS YIELDS NE MOTIONS 50-60 KT FOR ANY SUSTAINED/DISCRETE
CELLS...WHICH SHOULD BE SFC-BASED FOR MUCH OF MID-LATE AFTERNOON.
EVEN MODEST CONVECTIVE GUSTS MAY BECOME DAMAGING WHEN SUPERIMPOSED
UPON GRADIENT FLOW THAT BY ITSELF MAY APCH CONVECTIVE SVR CRITERIA
IN HIGHER ELEVATIONS. WHILE STG DEEP-LAYER SPEED SHEAR ASSOCIATED
WITH SUCH INTENSE AMBIENT WINDS ABOVE SFC SEEMINGLY WOULD FAVOR SVR
POTENTIAL...MRGL BUOYANCY MAY BE IMPORTANT LIMITING FACTOR...GIVEN
ASSOCIATED DIFFICULTY MAINTAINING UPRIGHT CONVECTIVE PLUMES.
MLCAPES GENERALLY SHOULD REMAIN AOB 300 J/KG IN MOST AREAS...EVEN
DURING PEAK LATE AFTERNOON SFC TEMPS.
..NRN HIGH PLAINS...
INTERMOUNTAIN REGIME WILL TRANSITION/EXTEND NWD OVER NRN HIGH PLAINS
LATER IN PERIOD...WITH SOME ENHANCED/ELEVATED BUOYANCY RELATED TO
STRONG LOW LEVEL WAA/MOIST ADVECTION REGIME. ASSOCIATED STEEPENING
OF LOW-MIDDLE LEVEL LAPSE RATES ABOVE BOUNDARY LAYER WILL SUPPORT
MUCAPES 1000-1500 J/KG...AMIDST EFFECTIVE SHEAR IN 50-60 KT RANGE.
ALTHOUGH NOCTURNAL BOUNDARY LAYER STABILIZATION WILL MITIGATE
DAMAGING WIND POTENTIAL...TSTMS OVER ERN MT/WRN DAKOTAS MAY PRODUCE
OCCASIONAL HAIL.
.EDWARDS/CROSBIE.. 10/05/2007
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