SPC AC 191253
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0753 AM CDT WED AUG 19 2009
VALID 191300Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PART OF THE SRN HIGH
PLAINS INTO THE MID/UPPER MS RIVER VALLEY...
...PLAINS STATES...
UNSEASONABLY STRONG SHEAR WILL OVERSPREAD THE CENTRAL AND PARTS OF
THE NRN PLAINS ASSOCIATED WITH DEEP MID/UPPER LEVEL TROUGH
AMPLIFYING OVER THE UPPER MS RIVER VALLEY THROUGH TONIGHT. MORNING
WV IMAGERY INDICATES SEVERAL LOWER AMPLITUDE TROUGHS ROTATING AROUND
THIS BROADER TROUGH...EACH MAY FOCUS A SERIES OF CLUSTERS/MCS
DEVELOPMENT THROUGH THE PERIOD. DESPITE THE PRONOUNCED DEEP LAYER
SHEAR...SEVERE THUNDERSTORM FORECAST FOR LATER TODAY/TONIGHT REMAINS
QUITE COMPLEX AS MUCH OF THE REGION HAS BEEN IMPACTED BY PRECEEDING
CONVECTIVE COMPLEXES OVER THE PAST COUPLE DAYS. APPEARS UPGRADE IN
SEVERE PROBABILITIES MAY BE NEEDED IN LATER OUTLOOKS WITHIN THIS
BROADER SLGT RISK...ALTHOUGH TOO MANY UNCERTAINTIES REMAIN TO
CAPTURE GREATER RISK AREAS ATTM.
MORNING MCS NOW MOVING INTO NWRN MO WILL LIKELY CONTINUE INTO THE
EARLY AFTERNOON AHEAD OF SHORTWAVE TROUGH WHICH EJECTED OUT OF THE
CENTRAL ROCKIES TUESDAY NIGHT...SLOWING DESTABILIZATION OVER THE
LOWER MO/MID MS RIVER VALLEYS. ATTM...EXPECT POCKETS OF MORNING
HEATING SHOULD INCREASE SEVERE THREAT DURING THE MID TO LATE
AFTERNOON AHEAD OF THIS SYSTEM WHICH WILL LIFT STEADILY NEWD TOWARDS
THE UPPER MS RIVER VALLEY TODAY. GIVEN STRONG DEEP LAYER SHEAR AND
INCREASED LOW LEVEL SHEAR INVOF SSWLY LLJ/SFC WARM FRONT...SUPERCELL
AND POTENTIAL FOR TORNADOES SHOULD INCREASE FROM PARTS OF THE LOWER
MO INTO THE UPPER MS RIVER VALLEYS WHERE HEATING CAN SUPPORT MODEST
MLCAPE. ADDITIONAL DEVELOPMENT SHOULD OCCUR FARTHER WEST SHIFTING
ACROSS THE ERN DAKOTAS INTO ERN NEB LATER TODAY ALONG ESEWD MOVING
COLD FRONT AND IN ADVANCE OF YET ANOTHER DIGGING SHORTWAVE TROUGH
MOVING OUT OF THE NRN PLAINS. A MYRIAD OF CONVECTIVE STORM
EVOLUTIONS ACROSS THIS AREA IS EXPECTED TO SUSTAIN A RISK OF
DAMAGING WINDS AND ISOLATED LARGE HAIL INTO TONIGHT.
DEPENDING ON AMOUNT OF HEATING/RECOVERY IN WAKE OF EXTENSIVE EARLY
MORNING MCS OVER OK/KS...ISOLATED TO SCATTERED STRONG/SEVERE
THUNDERSTORM DEVELOPMENT SHOULD OCCUR INVOF RESIDUAL SURFACE OUTFLOW
BOUNDARY/FRONT EXTENDING SW-NE FROM PARTS OF WRN OK INTO WRN MO LATE
THIS AFTERNOON. VERY STEEP LAPSE RATES WILL INCREASE SEVERE
POTENTIAL AS STORMS EVOLVE AS MULTICELL CLUSTERS/LINES AND A FEW
SUPERCELLS. THUNDERSTORM POTENTIAL MAY INCREASE AFTER DARK AS DEEP
ASCENT INCREASES WITHIN STRENGTHENING LOW LEVEL WAA REGIME OVERNIGHT
ATOP SEWD MOVING SURFACE FRONT.
...MS RIVER VALLEY EWD TOWARDS THE MID ATLANTIC COAST...
BROAD AREA OF MARGINAL TO MODERATE INSTABILITY WITHIN LARGE
RESERVOIR OF DEEP MOISTURE CAN BE EXPECTED DURING THE DAY OVER THE
REGION. INSTABILITY WILL BE MORE LIMITED EAST OF THE LOWER
LAKES...HOWEVER SEWD SHIFTING SURFACE COLD FRONT MAY FOCUS
THUNDERSTORM DEVELOPMENT OVER THIS AREA. MODEST WLY LOW TO MID LEVEL
WINDS SHOULD ONCE AGAIN SUSTAIN A FEW CLUSTERS OF STRONG TO
MARGINALLY SEVERE STORMS THIS AFTERNOON AND EARLY EVENING WITH
POTENTIAL FOR WIND DAMAGE WHERE LOCAL STEEPENING OF LOW LEVEL LAPSE
RATES OCCURS.
..EVANS/JEWELL.. 08/19/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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