SWODY2
SPC AC 171718
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1218 PM CDT WED AUG 17 2011
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS NRN PLAINS...UPPER-MS
VALLEY...CNTRL PLAINS...MID MO VALLEY AND NRN OZARKS...
...NRN PLAINS/UPPER MS VALLEY/MID MO VALLEY...
AN UPPER-LEVEL RIDGE WILL BE IN PLACE THURSDAY ACROSS THE CNTRL
ROCKIES WITH WEST TO NORTHWEST FLOW LOCATED FROM THE NRN PLAINS TO
THE MID MS VALLEY. AT THE SFC...A COLD FRONT WILL ADVANCE SEWD
ACROSS THE NRN PLAINS AND UPPER MS VALLEY. AHEAD OF THE FRONT...A
BROAD ZONE OF MODERATE TO STRONG INSTABILITY SHOULD EXIST BY MID-DAY
ON THURSDAY ACROSS THE NRN PLAINS...UPPER MS VALLEY SEWD INTO THE
OZARKS AND MID MS VALLEY. THUNDERSTORM DEVELOPMENT IS FORECAST TO BE
MOST NUMEROUS ALONG AND JUST AHEAD OF THE FRONTAL BOUNDARY THURSDAY
AFTERNOON BUT POCKETS OF SCATTERED CONVECTION SHOULD INITIATE SEWD
ACROSS THE WARM SECTOR. SEVERAL THUNDERSTORM CLUSTERS SHOULD PERSIST
INTO THE EVENING AS A FRAGMENTED LOW-LEVEL JET STRENGTHENS ACROSS
THE REGION.
FORECAST SOUNDINGS THURSDAY AFTERNOON SHOW THE STRONGEST INSTABILITY
FROM CNTRL NEB NNEWD THROUGH ERN SD INTO WRN MN WHERE MLCAPE VALUES
ARE FORECAST TO BE FROM 2500 TO 4000 J/KG. IN ADDITION...MODERATE TO
STRONG DEEP LAYER SHEAR SHOULD EXIST ACROSS THE WARM SECTOR AS
MID-LEVEL FLOW INCREASES DUE TO A SUBTLE SHORTWAVE TROUGH MOVING
ESEWD OUT OF THE TOP OF THE UPPER-LEVEL RIDGE. THE
INSTABILITY...SHEAR AND LARGE-SCALE ASCENT SHOULD BE ADEQUATE FOR A
SEVERE THREAT ACROSS MUCH OF SD AND MN EXTENDING SWD INTO THE OMAHA
AREA FROM LATE THURSDAY AFTERNOON INTO THE EVENING. ALTHOUGH THE
SHEAR ENVIRONMENT WILL BE SUPPORTIVE OF SUPERCELL DEVELOPMENT...THE
DOMINANT STORM MODE MAY DEPEND ON WHETHER STORMS LINE OUT ALONG THE
FRONTAL BOUNDARY. IF SUPERCELL STRUCTURES CAN PERSIST...THEN THE
STEEP MID-LEVEL LAPSE RATES SHOULD AID A THREAT FOR LARGE HAIL. THE
HAIL THREAT WOULD BE GREATEST IN AREAS WHERE INSTABILITY IS
MAXIMIZED. A WIND DAMAGE THREAT SHOULD ALSO EXIST ESPECIALLY WITH IF
A LINEAR MCS CAN DEVELOP AND MOVE SEWD ACROSS THE SLIGHT RISK AREA
THURSDAY EVENING. A TORNADO THREAT COULD ALSO DEVELOP BUT THIS
THREAT SHOULD BE CLOSELY TIED TO HOW MANY STORMS CAN REMAIN
DISCRETE. THE NAM AND GFS ARE IN GOOD AGREEMENT ON THE TIMING OF THE
SHORTWAVE TROUGH SUGGESTING THE GREATEST SEVERE THREAT SHOULD EXIST
FROM NCNTRL SD SEWD INTO ERN NEB AND WRN IA WHERE AN ENHANCED SEVERE
THREAT MAY BE WARRANTED IN THE OUTLOOK. ATTM...WILL DEFER AN UPGRADE
TO 30 PERCENT SEVERE PROBABILITY TO LATER OUTLOOKS. NEW MODEL RUNS
SHOULD HELP BETTER PINPOINT THE EXACT CORRIDOR OF AN ENHANCED SEVERE
THREAT.
FURTHER SOUTHEAST ACROSS THE CNTRL PLAINS...OZARKS AND MID MS
VALLEY...FORECAST SOUNDINGS AT 21Z THURSDAY SHOW MODERATE
INSTABILITY WITH 30 TO 40 KT OF DEEP LAYER SHEAR SUGGESTING THE
ENVIRONMENT SHOULD SUPPORT A SEVERE THREAT. ISOLATED LARGE HAIL AND
WIND DAMAGE MAY OCCUR ESPECIALLY IF A CONVECTIVE CLUSTER CAN
ORGANIZE AND PERSIST INTO THURSDAY EVENING.
..BROYLES.. 08/17/2011
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