SWODY2
SPC AC 061724
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1224 PM CDT WED JUN 06 2007
VALID 071200Z - 081200Z
..THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF NERN MO...ERN
IA...NWRN IL...WI...EXTREME ERN MN AND THE MI U.P....
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MIDWEST/GREAT
LAKES SWWD ACROSS THE MID MS VALLEY AND INTO PORTIONS OF THE SRN
PLAINS...
..WIDESPREAD SEVERE WEATHER OUTBREAK...WITH SOME SIGNIFICANT
EVENTS...IS LIKELY FROM THE WRN/CENTRAL GREAT LAKES REGION SWWD
THROUGH THE MID MS VALLEY AND INTO PORTIONS OF THE SRN PLAINS ON
THURSDAY...
..SYNOPSIS...
AN UNSEASONABLY INTENSE UPPER LOW IS FORECAST TO LIFT NEWD FROM SD
INTO SRN ONTARIO DURING THE DAY. AN UPPER TROUGH EXTENDING SWD FROM
THIS SYSTEM...AND ACCOMPANYING COLD FRONT...IS EXPECTED TO
SWEEP EWD INTO THE WRN GREAT LAKES/MID MS VALLEY AND INTO TX/OK
PANHANDLES BY LATE AFTERNOON...WITH A DRYLINE EXTENDING FROM THE
FRONT IN EXTREME SRN KS SWD ACROSS WRN OK/TX. AS A RESULT OF THE
DEEP UPPER TROUGH AND HIGH PRESSURE SYSTEM OVER THE SERN STATES...
VERY STRONG WIND FIELDS WILL EXTEND ACROSS THE SLIGHT/MODERATE RISK
AREAS...WITH SWLY MID LEVEL WINDS FROM 60-80 KT ACROSS THE SRN
PLAINS AND 80-100 KT ACROSS THE REMAINDER OF THE AREA.
..UPPER MIDWEST/GREAT LAKES...
STORMS SHOULD BE ONGOING AT THE START OF THE PERIOD ACROSS PARTS OF
THE ND/MN...WITH MARGINAL SEVERE WEATHER POSSIBLE AS REMNANT
OVERNIGHT CONVECTION SHIFTS NEWD INTO ONTARIO.
ONCE ELEVATED CONVECTION SHIFTS EWD THROUGH WI/ERN IA/ERN MN
TODAY...REMAINDER OF RISK AREA SHOULD REMAIN MOSTLY CONVECTIVE FREE
UNTIL SOMETIME THURSDAY AFTERNOON. ALTHOUGH RICHER GULF MOISTURE/70
DEGREE DEWPOINTS/ ARE LIKELY TO ADVECT ONLY AS FAR NORTH AS
MO...LOWER TO MID 60 DEWPOINTS AND 850-500MB LAPSE RATES NEAR 7C/KM
SHOULD SUPPORT MLCAPES FROM 1500 TO 3000 J/KG. RELATIVELY WARM MID
LEVEL TEMPERATURES SHOULD INHIBIT CONVECTIVE DEVELOPMENT THROUGH
MIDDAY...WITH INCREASING LARGE SCALE ASCENT/LOW LEVEL CONVERGENCE
PROVIDE FAVORABLE ENVIRONMENT FOR NUMEROUS THUNDERSTORMS TO DEVELOP
ALONG AND AHEAD OF THE FRONT BY MID AFTERNOON. ALTHOUGH WIND
PROFILES ACROSS ERN MN/WI/U.P. ARE FORECAST TO VEER WEAKLY WITH
HEIGHT...EXTREME SPEED SHEAR IS INDICATED ON FORECAST
SOUNDINGS...RESULTING IN 60 TO 70 KT OF EFFECTIVE SHEAR. THESE
EXTREME SHEAR VALUES AND INSTABILITY WILL FAVOR RAPID SUPERCELL
GROWTH...ONCE STORMS DEVELOP. THE 20-30 KT 1KM SHEAR AND MOISTENING
BOUNDARY LAYER WOULD ALSO SUPPORT A TORNADO THREAT...SOME
STRONG...DURING THE LATE AFTERNOON/EVENING HOURS. ALTHOUGH THE
STORMS MAY EVOLVE INTO THE LINE...WHICH WOULD ENHANCE THE THREAT FOR
DAMAGING WINDS...THE AMOUNT OF SHEAR SHOULD ALSO SUPPORT EMBEDDED
TORNADIC SUPERCELLS WITHIN LINEAR SYSTEM. BY EVENING...STORMS SHOULD
EVOLVE INTO A FAST EWD MOVING LINE..WITH SEVERE WIND THREAT
SPREADING INTO THE CENTRAL GREAT LAKES OVERNIGHT.
..MID MS VALLEY SWWD INTO THE SRN PLAINS...
VERY WARM TEMPERATURES ALOFT SHOULD LIMIT CONVECTION THROUGH A
MAJORITY OF THE AFTERNOON...WHICH WILL ALLOW SURFACE TEMPERATURES TO
WARM WELL INTO THE 80S AND LOWER 90S. SRN/WRN TX SOUNDINGS THIS
MORNING AND CU FIELD...ALONG WITH LOWER 70 DEWPOINTS...INDICATE
RICHER GULF MOISTURE HAS FINALLY SHIFTED NWD FROM THE WRN GULF INTO
SRN TX. SURFACE FALLS ACROSS THE CENTRAL PORTIONS OF THE COUNTRY AND
STRENGTHENING SLY WINDS WILL ADVECT 70+ DEGREE DEWPOINTS NWD...AHEAD
OF THE FRONT AND EAST OF DRYLINE ON THURSDAY...AT LEAST AS FAR NWD
AS MO. THIS WILL RESULT IN VERY STRONG INSTABILITY THURSDAY
AFTERNOON WITH MLCAPES FROM 2500-3500 J/KG. ALTHOUGH THE FORCING
WILL NOT BE QUITE AS STRONG AS ACROSS THE GREAT LAKES
REGION...INTENSE HEATING AND CONVERGENCE ALONG THE FRONT SHOULD
SUPPORT NUMEROUS STORMS DEVELOPING ALONG AND EAST OF THE FRONT/DRY
LINE BY LATE AFTERNOON. ONCE STORMS DEVELOP...DEEP LAYER SHEAR AT
50-70 KT WILL SUPPORT NUMEROUS SUPERCELLS. THE DEGREE OF INSTABILITY
AND SHEAR CERTAINLY SUGGEST A TORNADO THREAT...THOUGH HIGHER LCL
HEIGHTS AND 1 KM SRH FROM 100-150 M2/S2 INDICATE THAT WIND DAMAGE
AND LARGE HAIL SHOULD BE THE MAIN THREATS. DUE TO THE STRONG
INSTABILITY...SCATTERED SEVERE STORMS ARE LIKELY TO PERSIST WELL
INTO THE NIGHT.
.IMY.. 06/06/2007
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