SPC AC 140600
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT TUE JUL 14 2009
VALID 141200Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER
MIDWEST...MID-MO VALLEY...CNTRL AND NRN PLAINS...
...UPPER MIDWEST/MID-MO VALLEY/CNTRL AND NRN PLAINS...
A WELL-DEVELOPED UPPER-LEVEL TROUGH WILL MOVE ACROSS THE NRN PLAINS
TODAY. AHEAD OF THE APPROACHING TROUGH...A 40 TO 50 KT LOW-LEVEL JET
WILL SET UP FROM NRN MO EXTENDING NWD ACROSS IA AND MN. AN MCS WITH
MARGINALLY SEVERE STORMS SHOULD BE ONGOING WEST OF THE LOW-LEVEL JET
THIS MORNING. THE MCS IS EXPECTED TO GRADUALLY WEAKEN THROUGH MIDDAY
WITH REDEVELOPMENT OCCURRING TO THE WEST ALONG AN AXIS OF MODERATE
TO STRONG INSTABILITY THIS AFTERNOON. THE MODELS PRESENT SEVERAL
DIFFERENT SCENARIOS. ATTM...AM FAVORING A COMPROMISE BETWEEN THE GFS
AND NAMKF WITH STORMS INITIATING IN THE ERN DAKOTAS EARLY THIS
AFTERNOON AND A SQUALL-LINE DEVELOPING IN MN AND IA DURING THE LATE
AFTERNOON AND EARLY EVENING. SOUTH OF THE SQUALL-LINE IN THE MID-MO
VALLEY...CONVECTION SHOULD BE MORE SCATTERED IN COVERAGE. A LARGE
MCS IS EXPECTED TO ORGANIZE AND MOVE QUICKLY ESEWD ACROSS ERN
MN...ERN IA INTO WI...NRN IL AND NRN MO DURING THE OVERNIGHT PERIOD.
CONCERNING THE SEVERE POTENTIAL...MODEL FORECASTS AGAIN FORECAST
SUBSTANTIAL DESTABILIZATION TODAY WITH A POCKET OF STRONG
INSTABILITY IN THE MID-MO VALLEY. A BROAD CORRIDOR OF MODERATE
INSTABILITY IS FORECAST FROM ERN NEB AND IA NWD TO THE MN-CANADIAN
BORDER. THE AMOUNT OF INSTABILITY COMBINED WITH LIFT AHEAD OF THE
APPROACHING UPPER-LEVEL TROUGH SUGGESTS A POTENTIAL FOR STRONG
UPDRAFTS WILL EXIST ACROSS A BROAD AREA. A 50-60 KT MID-LEVEL JET
ASSOCIATED WITH THE UPPER-LEVEL TROUGH WILL OVERSPREAD THE
INSTABILITY AXIS THIS AFTERNOON CREATING STRONG VERTICAL SHEAR
SUFFICIENT FOR SUPERCELLS. HOWEVER...WHETHER SUPERCELLS CAN REMAIN
THE DOMINANT MODE REMAINS QUESTIONABLE. THE CURRENT THINKING IN THE
UPPER MIDWEST IS THAT SUPERCELLS WITH LARGE HAIL AND TORNADO
POTENTIAL WILL BE FAVORED EARLY WITH A FAIRLY QUICK TRANSITION TO A
SQUALL-LINE. THE GREATEST TORNADO THREAT SHOULD OCCUR FROM SRN MN
SWD ACROSS WRN IA INTO NW MO PRIOR TO SQUALL-LINE DEVELOPMENT WHEN
INSTABILITY AND LOW-LEVEL SHEAR SHOULD BE MAXIMIZED. FURTHER SOUTH
IN THE MID-MO VALLEY WHERE STRONG INSTABILITY IS FORECAST AND TEMPS
ALOFT WILL BE WARMER...THE STORMS MAY TEND REMAIN DISCRETE LONGER.
SUPERCELLS IN THE STRONGLY UNSTABLE ENVIRONMENT ACROSS NE KS...NW MO
AND WRN IA MAY PRODUCE ISOLATED VERY LARGE HAIL. EVENTUALLY...THE
STORMS ACROSS THE MID-MO VALLEY MAY ALSO CONGEAL INTO AN MCS OR
LARGE CONVECTIVE CLUSTER. A WIND DAMAGE THREAT SHOULD EXIST WITH ANY
CONVECTIVE CLUSTER OR MCS THAN CAN PERSIST DURING THE OVERNIGHT
PERIOD. HOWEVER...THE SEVERE THREAT SHOULD BECOME INCREASINGLY
MARGINAL DUE TO WEAKENING INSTABILITY WITH EWD EXTENT.
..BROYLES/JEWELL.. 07/14/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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