SWODY1
SPC AC 201240
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0740 AM CDT MON SEP 20 2010
VALID 201300Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE WRN GREAT LAKES AND
UPPER MS VALLEY REGIONS...
...SYNOPSIS...
UPPER-LEVEL SHORTWAVE TROUGH OVER THE INTERMOUNTAIN W WILL PROGRESS
QUICKLY EWD INTO THE UPPER MS VALLEY THROUGH TONIGHT. AT THE
SURFACE...LEE LOWS OVER ERN WY AND NERN CO WILL CONSOLIDATE THIS
AFTERNOON IN SWRN NEB...THEN DEEPEN WHILE MOVING INTO SWRN MN BY
THIS EVENING AND THE UPPER GREAT LAKES BY 12Z TUESDAY. TRAILING THE
LOW...A COLD FRONT WILL SWEEP SEWD... REACHING THE RED RIVER...SERN
SD AND WRN NEB BY THIS EVENING AND THE UPPER MS VALLEY...CORN
BELT...CNTRL PLAINS REGION BY 12Z TUESDAY.
...UPPER GREAT LAKES SWWD INTO MN/IA....
A BROAD ZONE OF STRONG LLVL SLY FLOW IS EXPECTED TO BE MAINTAINED
TODAY AHEAD OF THE APPROACHING UPPER TROUGH...RESULTING IN STRONG
WAA AND MOISTURE TRANSPORT INTO THE REGION. POCKET OF 1.5 INCH
PRECIPITABLE WATER/60S SURFACE DEW POINTS WILL LIKELY BE DRAWN NWD
AS FAR N AS NRN MN/WI BY SUNSET. EXPECTATION IS FOR THE REGION TO
REMAIN CAPPED UNTIL EVENING.
THUNDERSTORM PROBABILITIES WILL BEGIN TO ESCALATE OVER NRN MN IN THE
00-03Z TIME FRAME AS LARGE-SCALE FORCING ASSOCIATED WITH THE
TROUGH/COLD FRONT BEGINS TO ARRIVE. THIS ACTIVITY WILL PROBABLY BE
MOSTLY ELEVATED AS IT QUICKLY EVOLVES ENE TOWARD THE UPPER GREAT
LAKES DURING THE NIGHT. GIVEN EXPECTED STEEP MID-LEVEL LAPSE RATES
AND FAVORABLE CLOUD-BEARING SHEAR...THREAT FOR BRIEF SUPERCELLS
EMBEDDED WITHIN STRONG CLUSTERS/BANDS WILL EXIST WITH LARGE HAIL AND
POSSIBLE DAMAGING WIND GUSTS.
MEANWHILE...AS THE COLD FRONT BEGINS TO SURGE SEWD...ACCELERATED
COOLING/MOISTENING ALOFT COINCIDENT WITH SRN FRINGE OF THE TROUGH
WILL GIVE RISE TO SCATTERED THUNDERSTORMS FROM CNTRL MN/NRN WI SWWD
TOWARD NRN IA. THESE STORMS WILL HAVE A HIGHER PROBABILITY TO BE
NEAR-SURFACE BASED. DEEP-LAYER...LARGELY UNIDIRECTIONAL WSW FLOW
REGIME OF 50+ KTS MAY YIELD A FEW ORGANIZED SMALL-SCALE BOWS CAPABLE
OF DAMAGING WINDS/HAIL AS THEY RACE ENE DURING THE NIGHT. NEGATIVES
FOR A MORE WIDESPREAD SEVERE EVENT WILL BE THE NOCTURNAL TIMING AND
UNCERTAINTY ON THE NUMBER OF STORMS.
...CENTRAL PLAINS...
COMPARATIVELY STRONGER HEATING WILL OCCUR ALONG/AHEAD OF A
PRE-FRONTAL TROUGH TODAY...ALTHOUGH AIR MASS WILL REMAIN CAPPED FOR
MOST OF THE AFTERNOON AS LLVL MOISTURE ADVECTION IS OFFSET BY
TURBULENT MIXING. BY LATE AFTERNOON...MULTI-MODEL CONSENSUS
SUGGESTS POTENTIAL FOR CONVECTIVE INITIATION NEAR THE TROUGH AS CINH
WEAKENS FROM PARTS OF ERN CO NEWD INTO SW-CENTRAL NEB. MAINLY
MULTICELL STORM MODES ARE EXPECTED WITH HIGH-BASED STORMS PRIMARILY
PRODUCING ISOLATED SEVERE WIND GUSTS/HAIL. WHILE ACTIVITY
DIMINISHES DURING THE EVENING...SOME REDEVELOPMENT MAY OCCUR
DOWNSTREAM ALONG THE PRIMARY COLD FRONT LATE AT NIGHT...PRIMARILY AT
POINTS FROM THE MO RIVER NE TOWARD THE UPPER MS VALLEY.
..RACY/SMITH.. 09/20/2010
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