SWODY1
SPC AC 211945
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0245 PM CDT THU JUN 21 2007
VALID 212000Z - 221200Z
..THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF ERN IA...
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PART OF THE
NRN/CENTRAL HIGH PLAINS EWD INTO THE OH VALLEY AND NORTHEAST...
..NRN HIGH PLAINS SEWD INTO IL...
STRONG/SEVERE CLUSTER OF STORMS WAS MOVING THROUGH NWRN IA...
REFERENCE WW 434...AND SHOULD CONTINUE TO MOVE SEWD JUST SOUTH OF A
WARM FRONT...THAT AT MID AFTERNOON STRETCHED FROM NEAR THE MN/IA
BORDER SEWD INTO NRN IL. DAYTIME HEATING HAS RESULTED IN THE AIR
MASS TO BECOME STRONGLY UNSTABLE AHEAD OF STORMS...WITH MLCAPE
VALUES AROUND 3000 J/KG. THE COMBINATION OF AN EXPECTED COLD POOL
DEVELOPMENT LATER THIS AFTERNOON AND 30 KT MID LEVEL NWLY WINDS
SHOULD INCREASE THE DAMAGING WIND THREAT...AS THE STORMS BEGIN TO
ACCELERATE SEWD INTO ERN IA. VEERING LOW LEVEL JET AND INCREASING
INSTABILITY TONIGHT SHOULD PROPEL STORMS SEWD ALONG THE FRONT INTO
CENTRAL IL...AND POSSIBLY INTO CENTRAL/SRN INDIANA LATE
TONIGHT...WITH A CONTINUED DAMAGING WIND THREAT.
AS CONVERGENCE INCREASES AND WEAKENS THE CAP ACROSS NEB NEAR SURFACE
LOW AND ALONG STATIONARY FRONT LOCATED IN NRN NEB... THUNDERSTORMS
SHOULD DEVELOP LATER THIS AFTERNOON. VERY STRONG INSTABILITY...
MLCAPES NEAR 4000 J/KG...AND 30 KT DEEP LAYER SHEAR WILL BE MORE
THAN ADEQUATE FOR SEVERE STORMS WITH LARGE HAIL. STRENGTHENING LOW
LEVEL JET AND SURFACE BOUNDARY MAY RESULT IN STORMS EVOLVING INTO AN
EWD MOVING MCS TONIGHT...WHICH WOULD INCREASE THE WIND THREAT.
ALTHOUGH THE NRN PLAINS ARE NORTH OF SURFACE FRONT...LARGE SCALE
LIFT AND HEATING OF RELATIVELY MOIST BOUNDARY LAYER SHOULD RESULT IN
ADDITIONAL STRONG/SEVERE STORM CLUSTERS TO DEVELOP ACROSS PORTIONS
OF FAR ERN MT/NERN WY/ND/SD THIS AFTERNOON/EVENING. THE COMBINATION
OF MODERATE INSTABILITY AND SELY BOUNDARY LAYER WINDS ...VEERING TO
NWLY AT 30-40 IN THE MID LEVELS...WILL BE SUFFICIENT FOR SUPERCELLS
AND ORGANIZED MCS CLUSTERS TO SPREAD SEWD ACROSS THE AREA LATER
TODAY AND TONIGHT.
..UPPER OH VALLEY EWD INTO THE NORTHEAST...
THE COMBINATION OF A SEWD MOVING COLD FRONT...THAT STRETCHED FROM
SWRN ONTARIO SWWD TO NEAR THE LOWER MI/OH/INDIANA BORDER...AND LIFT
ASSOCIATED WITH 50-60 KT NWLY MID LEVEL JET HAS RESULTED IN
SCATTERED TO NUMEROUS THUNDERSTORMS TO DEVELOP ACROSS THE REGION.
DESPITE WEAK INSTABILITY...STRONG ENVIRONMENTAL WIND FIELDS AND
STEEP LOW LEVEL LAPSE RATES WILL SUPPORT A SEVERE WIND THREAT...AND
SOME HAIL...GIVEN THE RELATIVELY COLD TEMPERATURES ALOFT.
.IMY.. 06/21/2007
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