SWODY3
SPC AC 040728
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0228 AM CDT SAT SEP 04 2010
VALID 061200Z - 071200Z
...SYNOPSIS...
00Z NAM/GFS/ECMWF GUIDANCE GENERALLY AGREE THAT A BASAL SHORTWAVE
PORTION OF THIS WEEKENDS NORTHWEST CONUS UPPER TROUGH WILL PIVOT
NORTHEASTWARD/TAKE ON A MORE NEGATIVE TILT FROM THE NORTHERN PLAINS
TO THE UPPER MS RIVER VALLEY ON LABOR DAY. ASSOCIATED
EAST-NORTHEASTWARD ADVANCING SURFACE LOW/COLD FRONT WILL FOCUS THE
PRIMARY DEEP CONVECTIVE POTENTIAL OVER THE UPPER MIDWEST/UPPER MS
RIVER VALLEY.
...UPPER MIDWEST/UPPER MS RIVER VALLEY...
CURRENT NUMERICAL GUIDANCE CONSENSUS SUGGESTS THAT THE BRUNT OF THE
AFOREMENTIONED UPPER TROUGH WILL BE CROSSING THE MIDDLE MO RIVER
VALLEY VICINITY MONDAY AFTERNOON...WITH APPRECIABLE LARGE SCALE
FORCING FOR ASCENT/HEIGHT FALLS FOCUSED DOWNSTREAM ACROSS PORTIONS
OF IA/MN TO THE ADJACENT UPPER MS RIVER VALLEY. THE RECENT COLD
FRONTAL PASSAGE /NOW ALONG THE GULF COAST/...AND THE RESIDUAL
INFLUENCE OF EASTERN STATES SURFACE HIGH PRESSURE/ASSOCIATED
TRAJECTORIES...WILL ONLY BE CONDUCIVE FOR A NARROW WARM MOIST SECTOR
/WITH LOWER 60S F SURFACE DEWPOINTS/ ALONG/AHEAD OF THE ADVANCING
SURFACE LOW/COLD FRONT MONDAY AFTERNOON/EVENING. CURRENT THINKING IS
THAT MODEST BOUNDARY LAYER MOISTURE AND AN EASTWARD ADVECTING
ELEVATED MIXED LAYER SHOULD GENERALLY CAP SURFACE BASED TSTM
DEVELOPMENT UNTIL LATE AFTERNOON...OR MORE LIKELY...EARLY EVENING
ALONG THE COLD FRONT. WHILE THE DEGREE OF DESTABILIZATION AND
TIMING/EXTENT OF DEEP CONVECTIVE DEVELOPMENT IS UNCERTAIN....AMPLE
LARGE SCALE FORCING ACCOMPANIED BY STEEP LAPSE RATES ALOFT AND
ROBUST WIND PROFILES /50-75 KT AT 500 MB WITH 45-50 KT AT 850 MB/
WILL LIKELY SUPPORT AT LEAST SOME SEVERE THREAT IN ASSOCIATION WITH
THE ADVANCING COLD FRONT. FORECAST STRONG BUT LARGELY UNIDIRECTIONAL
WIND PROFILES...IN CONJUNCTION WITH THE DEGREE OF/FRONTAL NATURE OF
THE FORCING...IMPLY THAT DAMAGING WINDS/PERHAPS A BRIEF TORNADO WILL
BE THE PRIMARY SEVERE CONCERNS.
IT SEEMS PROBABLE THAT A CATEGORICAL SLIGHT RISK WILL BE NEEDED IN
SUBSEQUENT OUTLOOKS FOR PORTIONS OF THE REGION...BUT AFOREMENTIONED
MODEST MOISTURE/INSTABILITY AND SOME LARGE SCALE UNCERTAINTY AT THIS
JUNCTURE PRECLUDE A SLIGHT RISK.
..GUYER.. 09/04/2010
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