SWODY1
SPC AC 200501
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1201 AM CDT TUE SEP 20 2011
VALID 201200Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A POTENT UPPER LOW AND CYCLONICALLY CURVED JET MAX WILL MOVE FROM
THE DAKOTAS INTO MN BY 00Z...BECOMING VERTICALLY STACKED WITH
SURFACE LOW. WHILE COOL ALOFT...LOW LEVEL MOISTURE WILL BE MEAGER
WITH ONLY 40S TO LOWER 50S BOUNDARY LAYER DEWPOINTS AHEAD OF THE
COLD FRONT...WHICH WILL BECOME OCCLUDED FROM ERN ND INTO NRN MN
DURING THE DAY. THIS WILL RESULT IN A HIGH SHEAR AND LOW CAPE
SITUATION...WITH ISOLATED SEVERE STORMS POSSIBLE. THE LOW CENTER
WILL DRIFT EWD OVERNIGHT INTO NRN WI/WRN MI U.P. BY 12Z WED...WITH A
WANING THUNDERSTORM THREAT OVERNIGHT.
ELSEWHERE...SCATTERED THUNDERSTORMS ARE EXPECTED OVER THE SERN
STATES...BUT WEAK SHEAR PROFILES BENEATH RISING HEIGHTS ALOFT ALONG
WITH POOR LAPSE RATE PROFILES SHOULD PRECLUDE ANY SEVERE THREAT
ASIDE FROM LOCALLY GUSTY WINDS.
...MN/WI/UPPER MI...
STRONG LIFT WILL EXIST EARLY ACROSS MUCH OF MN...IN A ZONE OF WARM
ADVECTION WITH A 40-50 KT SLY LOW LEVEL JET...AND WITH THE COLD
FRONT QUICKLY APPROACHING FROM THE W. INSTABILITY WILL BE WEAK...BUT
A ZONE OF SHOWERS AND EMBEDDED THUNDERSTORMS SHOULD BE ONGOING. THIS
ACTIVITY WILL MOVE QUICKLY EWD INTO WI BY 18Z...AND MAY POSE A
MARGINAL WIND/HAIL THREAT. STRONG SHEAR PROFILES AND WIND MAGNITUDES
DOWN LOW WOULD FAVOR WIND GUSTS...BUT TIME OF DAY MAY MITIGATE THIS
THREAT WITH POOR LAPSE RATES INITIALLY.
FARTHER N INTO THE MN ARROWHEAD NEAR THE TRIPLE POINT...CONVECTION
MAY BE BETTER TIMED WITH PEAK HEATING. SHEAR PROFILES WILL FAVOR
RELATIVELY LOW-TOPPED SUPERCELLS...CAPABLE OF MARGINALLY SEVERE
HAIL. THERE COULD BE A BRIEF WINDOW OF TIME NEAR PEAK HEATING FOR A
TORNADO...BUT ANY SUCH THREAT IS MINIMAL GIVEN POOR LAPSE RATES IN
THE LOW LEVELS AND WEAK INSTABILITY.
..JEWELL/ROGERS.. 09/20/2011
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