SWODY1
SPC AC 180557
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT SAT SEP 18 2010
VALID 181200Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
THE BASE OF A LARGE AND POWERFUL UPPER TROUGH WILL SHIFT EWD OUT OF
THE UPPER MS VALLEY AND INTO THE GREAT LAKES LATER TODAY. BEHIND
THIS TROUGH...GENERALLY ZONAL FLOW WILL REMAIN WITH SLIGHT UPPER
RIDGING. AT THE SURFACE...A COLD FRONT WILL STRETCH FROM ERN CO
ACROSS NERN KS AND INTO NRN IL WITH SURFACE HIGH PRESSURE CENTERED
OVER SD. A MOIST AXIS WILL EXTEND NWD ACROSS TX/OK INTO ERN KS/MO
WHERE STRONG INSTABILITY WILL INTERACT WITH THE BOUNDARY FOR
SCATTERED STORMS...SOME SEVERE.
...ERN NEB INTO THE LOWER MO/MID MS VALLEY...
CONVECTION IS LIKELY TO BE ONGOING AT THE START OF THE PERIOD...FROM
ERN NEB INTO IA AND IN A ZONE OF DEEP FRONTOGENETIC FORCING. SOME OF
THIS ACTIVITY MAY CONTAIN MARGINALLY SEVERE HAIL OWING TO COOL LAPSE
RATES ALOFT. FORCING ALONG THE FRONT WILL SHIFT EWD INTO NRN IL BY
AFTERNOON WHERE ONLY WEAK INSTABILITY WILL EXIST.
DURING THE DAY...STRONG DESTABILIZATION IS EXPECTED ACROSS THE WARM
SECTOR. SSWLY LOW LEVEL FLOW WILL IMPINGE UPON THE COLD
FRONT...AND/OR ANY EXISTING OUTFLOW BOUNDARIES FROM EARLIER
CONVECTION...WITH ADDITIONAL MAINLY ELEVATED DEVELOPMENT LIKELY.
WIND PROFILES WILL BE SUFFICIENT FOR SUPERCELLS MAINLY N OF THE
BOUNDARY...BUT LOW LEVEL SHEAR NEAR THE PRIMARY BOUNDARY/OUTFLOW MAY
BE SUFFICIENT FOR AN ISOLATED TORNADO. DEEP SHEAR DECREASES TO THE S
OVER THE WARM SECTOR. GIVEN UNCERTAINTIES WITH EVOLUTION OF
OVERNIGHT CONVECTION...AS WELL AS THE POTENTIAL FOR SHORTWAVE
RIDGING BEHIND THE EXITING UPPER TROUGH...WILL NOT ISSUE SLIGHT RISK
AT THIS TIME ALTHOUGH PORTIONS OF THE AREA MAY REQUIRE AN UPGRADE IN
SUBSEQUENT OUTLOOKS IF CONDITIONS WARRANT.
..JEWELL/GARNER.. 09/18/2010
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