SWODY1
SPC AC 310555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CDT TUE AUG 31 2010
VALID 311200Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER MS VALLEY TO
THE CENTRAL PLAINS...
...SYNOPSIS...
THE LARGE SCALE FLOW PATTERN WILL DEAMPLIFY TO A DEGREE/TREND MORE
PROGRESSIVE OVER THE CONUS THROUGH THE PERIOD. THIS WILL BE
HIGHLIGHTED BY THE NORTHEASTWARD EJECTION/ADVANCEMENT OF THE NEXT
PORTION OF A CURRENT WESTERN STATES UPPER TROUGH...WHICH WILL SPREAD
FROM THE GREAT BASIN TO THE NORTH-CENTRAL ROCKIES...AND EVENTUALLY
REACH THE UPPER MIDWEST/CANADIAN PRAIRIES TONIGHT. AT THE
SURFACE...A COLD FRONT PROGRESSING EAST-SOUTHEASTWARD ACROSS THE
UPPER MS RIVER VALLEY/CENTRAL PLAINS WILL SERVE AS THE PRIMARY FOCUS
FOR DEEP CONVECTIVE POTENTIAL LATER TODAY.
...UPPER MS VALLEY TO CENTRAL PLAINS...
QUASI-LINEAR BANDS OF SHOWERS/TSTMS WILL BE ONGOING EARLY THIS
MORNING ACROSS THE UPPER MS VALLEY VICINITY. CURRENT THINKING IS
THAT ANY EARLY PERIOD SEVERE THREAT WILL BE LIMITED BY THESE STORMS
OUTRUNNING THE PRIMARY INSTABILITY AXIS...IN ADDITION TO THE PRIMARY
LEAD MID LEVEL WAVE SHIFTING NORTHEASTWARD AWAY FROM THE REGION
EARLY THIS MORNING.
THIS EARLY DAY ACTIVITY DOES SUBSEQUENTLY PUT THE DEGREE OF
NEAR/PRE-FRONTAL DESTABILIZATION ACROSS THE UPPER MS VALLEY INTO
QUESTION...PRIMARILY UNCERTAIN ACROSS EASTERN MN/WESTERN WI.
NONETHELESS...AIDED BY THE GLANCING INFLUENCE OF THE NORTHERN PLAINS
UPPER TROUGH LATE THIS AFTERNOON/EVENING...TSTMS SHOULD INCREASE
ALONG THE EXTENT OF THE COLD FRONT DURING THE AFTERNOON...ACROSS
EASTERN/SOUTHERN MN...WESTERN WI...AND ESPECIALLY PORTIONS OF IA
WHERE STRONGER HEATING/DESTABILIZATION IS EXPECTED. ADDITIONAL
STRONG/SEVERE TSTMS SHOULD DEVELOP/EXPAND SOUTHWESTWARD BY EARLY
EVENING WITHIN A MODERATELY UNSTABLE CORRIDOR ALONG THE IMMEDIATE
SURFACE FRONTAL ZONE ACROSS PORTIONS OF SOUTHEAST NEB/FAR NORTHERN
KS AND FAR NORTHWEST MO. OVERALL...DAMAGING WINDS WILL BE THE
PRIMARY CONCERN WITH A DOMINANT MULTICELLULAR MODE...AS THE GREATEST
VERTICAL SHEAR/COOLING ALOFT WILL TEND TO LAG /NORTHWEST OF/ THE
COLD FRONT/INSTABILITY AXIS. HOWEVER...SEVERE HAIL/BRIEF TORNADO
POTENTIAL MAY EXIST ACROSS THE WESTERN HALF OF IA/SOUTHEAST NEB/FAR
NORTHERN KS/NORTHWEST MO...GIVEN A GREATER RESERVOIR OF INSTABILITY
COINCIDENT WITH MODERATE NEAR-FRONTAL DEEP LAYER/LOW LEVEL SHEAR.
...CENTRAL HIGH PLAINS LATE THIS AFTERNOON/EVENING...
WITHIN A DEVELOPING POST-FRONTAL MOIST UPSLOPE REGIME...ASSORTMENT
OF NUMERICAL GUIDANCE IMPLY THAT ISOLATED TSTM DEVELOPMENT MAY OCCUR
NEAR THE NORTHERN CO FRONT RANGE AND/OR ACROSS THE ADJACENT CENTRAL
HIGH PLAINS BY EARLY EVENING. AS STORMS DEVELOP/SPREAD EASTWARD THIS
EVENING ALONG/NORTH OF THE SURFACE FRONTAL ZONE...A HIGHLY
SHEARED/STEEP LAPSE RATE ENVIRONMENT MAY YIELD SOME STORMS CAPABLE
OF SEVERE HAIL/GUSTY WINDS.
...NORTHERN MAINE TODAY...
PERHAPS AIDED BY A WEAK MID LEVEL IMPULSE CROSSING QUEBEC/NORTHERN
MAINE DURING THE DAY AMID MODERATELY STRONG NORTHWESTERLY FLOW
ALOFT...IT APPEARS THAT ISOLATED TSTMS WILL BE POSSIBLE MAINLY
ACROSS NORTHERN MAINE THIS AFTERNOON IN CLOSE PROXIMITY TO A SURFACE
FRONT. CURRENT THINKING IS THAT ANY SEVERE POTENTIAL WILL REMAIN
VERY LOW...LARGELY ATTRIBUTABLE TO WARM TEMPERATURES/WEAK LAPSE
RATES ALOFT.
..GUYER/GRAMS.. 08/31/2010
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