SPC AC 120600
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT TUE MAY 12 2009
VALID 131200Z - 141200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF ILLINOIS AND
MISSOURI...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID TO
UPPER MS VALLEY...OZARKS...CNTRL PLAINS AND SRN PLAINS...
...SEVERE WEATHER OUTBREAK WITH TORNADOES POSSIBLE WEDNESDAY
AFTERNOON AND EVENING ACROSS THE MID TO UPPER MS VALLEY...
...MID TO UPPER MS VALLEY...
A PROGRESSIVE UPPER-LEVEL TROUGH AND WELL-DEFINED 75 TO 90 KT
MID-LEVEL JET WILL MOVE EWD ACROSS THE NRN PLAINS WEDNESDAY. AHEAD
OF THE SYSTEM...A BROAD LOW-LEVEL JET WILL BE IN PLACE WITH A LARGE
WARM SECTOR FROM THE SRN PLAINS NEWD ACROSS THE OZARKS INTO THE MID
TO UPPER MS VALLEY. A DEEPLY MOIST BOUNDARY LAYER...MODERATE
INSTABILITY...STRONG VERTICAL SHEAR AND IMPRESSIVE LOW-LEVEL SHEAR
PROFILES SHOULD RESULT A SIGNIFICANT SEVERE WEATHER EPISODE ACROSS
PARTS OF THE MID TO UPPER MS VALLEY. AN OUTBREAK OF SEVERE WEATHER
AND TORNADOES WILL BE POSSIBLE WEDNESDAY AFTERNOON AND EVENING.
THE LATEST CONSENSUS OF THE MODELS WEDNESDAY MORNING MOVE A CLUSTER
OF ELEVATED THUNDERSTORMS ASSOCIATED WITH THE LOW-LEVEL JET EWD
ACROSS THE OH VALLEY WEDNESDAY MORNING. THE TRACK OF THIS STORM
CLUSTER SHOULD BE IMPORTANT WITH THE MOST SUBSTANTIAL
DESTABILIZATION OCCURRING TO THE SOUTHWEST. BY THE TIME OF
INITIATION...IT APPEARS MODERATE INSTABILITY WILL BE IN PLACE FOR A
WIDESPREAD SEVERE WEATHER EVENT FROM CNTRL MO NEWD INTO WRN AND
CNTRL IL. NAMKF FORECAST SOUNDINGS OVER THIS AREA LATE WEDNESDAY
AFTERNOON SHOW 45 TO 50 KT OF VERTICAL SHEAR WITH 0-3 KM SRH VALUES
IN THE 250 TO 350 M2/S2 RANGE. THIS COMBINED WITH LOW LCL HEIGHTS
SHOULD BE FAVORABLE FOR SUPERCELLS WITH TORNADOES. FORECAST
HODOGRAPHS SUPPORT THE POTENTIAL FOR A FEW STRONG TORNADOES WITH THE
GREATEST POTENTIAL FROM CNTRL AND ERN IL SWWD ACROSS CNTRL AND ERN
MO IN THE LATE AFTERNOON OR EARLY EVENING. IN ADDITION...FORECAST
SOUNDINGS ACROSS THE MODERATE RISK AREA SHOW STEEP MID-LEVEL LAPSE
RATES WHICH SHOULD ALSO SUPPORT A THREAT FOR LARGE HAIL. DURING THE
EVENING...INCREASING LOW-LEVEL CONVERGENCE ALONG THE COLD FRONT MAY
RESULT IN A TRANSITION TO A LINEAR MODE. HOW QUICKLY THIS TRANSITION
OCCURS IS STILL IN QUESTION. IF A WELL-DEVELOPED LINEAR MCS OR
BOWING LINE SEGMENT CAN ORGANIZE...A SUBSTANTIAL WIND DAMAGE THREAT
WILL BE POSSIBLE AS WELL.
...SRN PLAINS/OZARKS...
MODEL FORECASTS MOVE THE SRN EXTENTION OF AN UPPER-LEVEL TROUGH
ACROSS THE CNTRL PLAINS WEDNESDAY. AT THE SFC...A COLD FRONT SHOULD
ADVANCE SWD ACROSS WRN MO...SE KS INTO NRN OK WITH A DEEPLY MOIST
BOUNDARY LAYER. AS A RESULT...GOOD CONFIDENCE EXISTS THAT STRONG
INSTABILITY WILL BE PRESENT ACROSS THE WARM SECTOR BY WEDNESDAY
AFTERNOON. ALTHOUGH THE GREATEST FORCING SHOULD BE TO THE
NORTHEAST...SCATTERED THUNDERSTORMS SHOULD DEVELOP AS LOW-LEVEL
CONVERGENCE INCREASES ALONG THE BOUNDARY LATE WEDNESDAY AFTERNOON.
FORECAST SOUNDINGS ACROSS NERN OK AND SW MO SHOW INCREASING VERTICAL
SHEAR TO ABOUT 45 KT BY EARLY WEDNESDAY EVENING AS THE RIGHT
ENTRANCE REGION OF THE MID-LEVEL JET AFFECTS THE AREA. THIS ALONG
WITH THE STRONG INSTABILITY AND STEEP MID-LEVEL LAPSE RATES SHOULD
SUPPORT SUPERCELL AND LARGE HAIL DEVELOPMENT. THE MORE DOMINANT
SUPERCELLS MAY HAVE THE POTENTIAL FOR VERY LARGE HAIL. FORECAST
SOUNDINGS ALSO SHOW STRONG LOW-LEVEL SHEAR PROFILES SUPPORTIVE OF
TORNADOES ESPECIALLY AS THE LOW-LEVEL JET INCREASES DURING THE EARLY
EVENING. A SIGNIFICANT SEVERE WEATHER EVENT COULD OCCUR ACROSS THE
SOUTHWEST PORTION OF THE SLIGHT RISK AREA. HOWEVER...UNCERTAINTY IS
GREATER THAN FURTHER NORTHEAST DUE TO A FURTHER PROXIMITY TO THE
UPPER-LEVEL TROUGH.
..BROYLES.. 05/12/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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