Potential Severe Weather

This is the SPC Discussion on the potential threat for severe weather. Hopefully David or I will be able to post a brief discussion this afternoon or evening after we get a chance to talk. Click on the map for a larger picture.

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0236 AM CDT TUE OCT 16 2007

...THERE IS A MDT RISK OF SVR TSTMS ACROSS MUCH OF IL AND INDIANA...SERN WI...SRN LOWER MI...AND PARTS OF WRN KY....

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE CONUS BETWEEN THE MS VALLEY AND THE APPALACHIANS...

...SYNOPSIS...

MID-LEVEL TROUGH CROSSING THE CENTRAL U.S. IS FORECAST TO INTENSIFY AND TAKE ON AN INCREASINGLY-NEGATIVE TILT WITH TIME. MEANWHILE...ASSOCIATED SURFACE LOW WILL MOVE FROM IA INTO THE UPPER GREAT LAKES REGION THROUGH THE PERIOD AS COLD FRONT SWEEPS EWD ACROSS THE MIDWEST/OH VALLEY AND SEWD ACROSS THE GULF COAST STATES THROUGH 19/12Z.

...ERN CONUS ROUGHLY FROM THE MS VALLEY EWD TO THE APPALACHIANS... WIDESPREAD/POTENTIALLY-SIGNIFICANT SEVERE WEATHER EVENT IS EVIDENT FOR DAY 3...AS LARGE UPPER TROUGH/LOW AND ASSOCIATED STRONG COLD FRONT MOVE EWD ACROSS THE MS VALLEY. AHEAD OF THE FRONT...A VERY LARGE WARM SECTOR IS ANTICIPATED...WHICH COMBINED WITH SOME DIURNAL HEATING SHOULD RESULT IN MARGINAL TO LOCALLY-MODERATE INSTABILITY.

ATOP THE MOIST/DESTABILIZING BOUNDARY LAYER...VERY STRONG DEEP TROPOSPHERIC WIND FIELD IS FORECAST TO OVERSPREAD THE FRONTAL ZONE INTO THE WARM SECTOR...WITH 60 TO 80 SSWLY FLOW AT MID-LEVELS FORECAST ATOP THE FRONT DURING THE AFTERNOON.

SCATTERED STORMS/STORM CLUSTERS SHOULD BE ONGOING ACROSS A LARGE PORTION OF THE AREA DURING THE DAY...WITH AN INCREASE IN CONVECTIVE INITIATION EXPECTED IN MULTIPLE BANDS CLUSTERS ALONG/AHEAD OF COLD FRONT AS IT CROSSES THE MS VALLEY DURING THE AFTERNOON. WHILE FLOW ROUGHLY PARALLEL TO THE FRONT DOES NOT APPEAR TO FAVOR NUMEROUS/PRIMARILY DISCRETE STORMS...STORM MODE IS IMPOSSIBLE TO DETERMINE AT THIS POINT. IT WOULD APPEAR THAT SOME COMBINATION OF ISOLATED AND LINEAR STORMS WILL BE ONGOING DURING THE AFTERNOON -- LIKELY PRODUCING HAIL/DAMAGING WINDS...AS SHEAR WILL BE STRONGLY-SUPPORTIVE OF LONG-LIVED/WELL-ORGANIZED STORMS. DEGREE OF LOW-LEVEL SHEAR AND PRESENCE OF MOIST BOUNDARY LAYER ALSO SUPPORTS A THREAT FOR TORNADOES.

ATTM...WILL INTRODUCE A MODERATE RISK ACROSS PARTS OF THE MIDWEST...WHICH MAY BE EXPANDED TO INCLUDE AREAS AS FAR S AS THE GULF COAST STATES IN LATER FORECASTS.

THREAT WILL LIKELY CONTINUE INTO THE OVERNIGHT HOURS...PERHAPS SHIFTING ACROSS THE APPALACHIANS LATE.