SPC AC 171733
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 PM CDT WED JUN 17 2009
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PART OF THE
NRN/CNTRL PLNS SEWD TO THE CAROLINAS...
....NRN PLNS INTO THE UPR MIDWEST...
POTENT UPR IMPULSE OVER AZ TODAY WILL EJECT ENE THROUGH THE CNTRL
ROCKIES TONIGHT...THEN ROUND THE PERIPHERY OF THE PLNS UPR RIDGE
INTO THE MO VLY THUR AFTN/EVE. NOCTURNAL MCS THAT EVOLVES OVER
NEB/CORN BELT TONIGHT WILL MOVE OFF INTO THE OH VLY THUR MORNING.
AIR MASS IN ITS WAKE WILL LIKELY RAPIDLY RECOVER AS SHORTWAVE
RIDGING TAKES HOLD THROUGH EARLY AFTN THUR ACROSS THE CORN BELT. BY
MID-AFTN...A NW-SE ORIENTED AXIS OF 70S SFC DEW POINTS COMBINED WITH
VERY STEEP MID-LVL LAPSE RATES WILL CONTRIBUTE TO VERY/EXTREMELY
UNSTABLE CONDITIONS FROM ERN SD SEWD TO IL.
STRONG HEATING...APCH OF THE AFOREMENTIONED DISTURBANCE AND
SUSTAINED LLVL CONVERGENCE INVOF THE RETURNING WRMFNT WILL
CONTRIBUTE TO TSTM INITIATION OVER THE CNTRL/ERN SD BY MID-AFTN.
OTHER HIGH-BASED STORMS MAY DVLP SWWD INTO NRN/ERN NEB ALONG A
LEE-TROUGH. INITIAL CELLS WILL LIKELY BE SUPERCELLS OWING TO
VERTICAL SHEAR ON THE ORDER OF 45-50 KTS. VERY LARGE HAIL AND DMGG
WINDS WILL BE LIKELY. TORNADO RISK WILL BE HIGHEST INVOF THE
WRMFNT/OUTFLOW BOUNDARY OVER ERN SD/SWRN MN/NWRN IA.
THERE IS GROWING CONCERN THAT ACTIVITY WILL EVOLVE INTO A BOWING MCS
OVERNIGHT THUR FROM SRN MN/NRN IA SEWD TOWARD EXTREME SRN WI AND
CHICAGOLAND. RICH BOUNDARY LAYER MOISTURE...INCREASING
WNWLY/LARGELY UNIDIRECTIONAL FLOW REGIME...PRESENCE OF A FORMIDABLE
BOUNDARY/FOCUSING MECHANISM WILL ALL BE CONDUCIVE FOR DMGG WIND
GUSTS/BOWS. PARTS OF THIS REGION MAY BE UPGRADED TO A MDT RISK IN
LATER OTLKS...ONCE EFFECTS FROM TONIGHT/S MCS IS BETTER KNOWN.
ATTM...WILL BOOST SVR PROBABILITIES TO ACCOUNT FOR THE ABOVE
SCENARIO.
...OH VLY TO SRN APLCNS...
MCV ASSOCD WITH EARLY DAY MCS OVER THE MID-MS VLY/LWR OH VLY WILL
PROGRESS SEWD INTO THE REGION DURING PEAK HEATING. SYSTEM WILL
BOOST WNWLY DEEP LAYER FLOW OVER THE REGION AMIDST VERY UNSTABLE
CONDITIONS INVOF A RETURNING WRMFNT. TSTMS WILL DEVELOP UPSTREAM
ACROSS SRN IND/WRN KY EARLY IN THE AFTN AS PSBL STG MULTICELLS/ISOLD
SUPERCELLS WITH LARGE HAIL...BUT THEN GROW UPSCALE INTO A BOWING
SYSTEM. ACTIVITY WILL LIKELY REACH THE SRN APLCNS DURING THE
EVENING WITH DMGG WIND GUSTS.
...MID-ATLC/CAROLINAS...
SRN PERIPHERY OF A MID-LVL WAVE...CURRENTLY MOVING ACROSS THE
GRTLKS/MIDWEST...WILL SKIRT ACROSS THE REGION ON THUR. SYSTEM WILL
BE ACCOMPANIED BY A BELT OF 35-45 KTS OF H5 FLOW...AUGMENTED BY
CONVECTIVELY-ENHANCED DISTURBANCES MOVING OUT OF THE OH VLY.
WARM SECTOR SHOULD BECOME WELL-ESTABLISHED ACROSS THE PIEDMONT/CSTL
PLAINS FROM SERN PA SWD INTO SC...WHERE PWATS SHOULD EXCEED 1.5
INCHES. THIS COMBINED WITH STEEP LLVL LAPSE RATES...SFC CONVERGENCE
INVOF A TROUGH AND DIFFERENTIAL HEATING ALONG THE HIGHER TERRAIN
SHOULD CONTRIBUTE TO TSTM INITIATION DURING THE AFTN. SOME STORMS
WILL BECOME STG TO SVR...WITH ISOLD SUPERCELLS POSSIBLE...BUT MORE
LIKELY LINE SEGMENTS THAT PRODUCE DMGG WINDS/HAIL. SVR RISKS ARE
SUFFICIENT TO ADD A SLGT RISK FOR THE REGION.
..RACY.. 06/17/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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