SPC AC 091256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT WED JUL 09 2008
VALID 091300Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE TN VLY/SRN APLCNS INTO
NC/VA...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NERN
STATES...
...SYNOPSIS...
SUMMER PATTERN WITH MAIN BELT OF WLYS CONFINED TO THE NRN TIER OF
STATES WILL PERSIST THROUGH THURSDAY. PROGRESSIVE TROUGH NOW OVER
ERN LK SUPERIOR/CNTRL ONT WILL MOVE E INTO WRN QUE BY THE END OF THE
PERIOD AS UPSTREAM DISTURBANCE NOW TAKING SHAPE OVER CNTRL MB
ACCELERATES SE ACROSS SW ONT TO THE MN ARROWHEAD/WRN LK SUPERIOR.
FARTHER S...FLAT SUB-TROPICAL HIGH WILL SPAN THE SRN STATES...WITH
CENTERS OVER THE WRN GRT BASIN AND THE CNTRL GULF CST.
AT THE SFC...COLD FRONT ASSOCIATED WITH LEAD IMPULSE WILL MOVE SE
INTO WRN NY AND THE UPR OH VLY BY EVENING. A MORE DIFFUSE
BOUNDARY...REPRESENTING COMPOSITE OUTFLOW FROM MCSS IN RECENT DAYS
...WILL PERSIST FROM DELMARVA/NC WSW INTO THE SRN PLNS. MEANWHILE
...EXPECT WRN END OF MAIN SYNOPTIC FRONT TO REDEVELOP N ACROSS THE
NRN PLNS AND UPR MS VLY LATER TODAY/TONIGHT AS STRONG SPEED MAX NOW
APPROACHING THE BC CST CONTINUES E INTO SRN AB/SK.
...TN VLY TO NC/VA THIS AFTN/EVE...
SATELLITE AND VWP DATA SHOW A WEAK IMPULSE OVER WRN IL...ALONG
WEAKNESS SEPARATING THE TWO SUB-TROPICAL HIGH CENTERS. THE
DISTURBANCE APPEARS TO HAVE ASSISTED IN THE OVERNIGHT MAINTENANCE OF
STORMS NOW IN WRN KY/TN. SFC HEATING SHOULD BOOST SBCAPE AHEAD OF
THE STORMS TO AOA 2500 J/KG OVER THE CUMBERLAND PLATEAU AND THE SRN
APLCNS. AREA VWPS SUGGEST THAT 25-30 KT UNIDIRECTIONAL WLY MID LVL
FLOW LIKELY WILL EXIST ACROSS REGION THIS AFTN. COUPLED WITH WEAK
FORCING FOR ASCENT PROVIDED BY UPR DISTURBANCE...AND UPSLOPE
COMPONENT TO FLOW...EXISTING STORMS COULD INCREASE IN
STRENGTH/ORGANIZATION. OTHER STORMS MAY FORM ALONG AND JUST E OF
THE MOUNTAINS IN NV/VA AS EXISTING CLOUDS CLEAR FROM THE W.
FORWARD-PROPAGATING SEGMENTS THROUGHOUT THE REGION COULD PRODUCE
DMGG WIND AND MARGINALLY SVR HAIL...MAINLY THIS AFTN THROUGH EARLY
TONIGHT.
...NERN U.S THIS AFTN/EVE...
VERY MOIST AIR MASS WILL PERSIST OVER THE NERN STATES AHEAD OF UPR
SYSTEM NOW CROSSING THE UPR GRT LKS. RADAR/SATELLITE LOOPS SHOW
WIDESPREAD CLOUDS/SHOWERS THAT WILL LIMIT SFC HEATING OVER MUCH OF
PA/NY TODAY. STRONGER HEATING WILL...HOWEVER...OCCUR FARTHER E OVER
INTERIOR PARTS OF NEW ENG. IF HEATING CAN OVERCOME WARM LYR AROUND
500 MB /PER AREA RAOBS/...TSTMS SHOULD FORM ALONG TERRAIN-INDUCED
CONVERGENCE ZONES IN HEATED AREA OF FAR ERN NY/INTERIOR NEW ENGLAND
TOWARD MIDDAY. MODEST UNIDIRECTIONAL WSWLY MID LVL FLOW MAY SUPPORT
DEVELOPMENT OF BROKEN LINES...WITH SMALL BOWING SEGMENTS POSSIBLY
PRODUCING LOCALLY DMGG GUSTS THIS AFTN/EARLY EVE.
...CNTRL HI PLNS TO LWR MO VLY THIS AFTN/EVE...
FAIRLY RICH MOISTURE WILL EXIST ALONG THE WRN PART OF PREVIOUSLY-
MENTIONED SYNOPTIC FRONT FROM SE NEB WNW INTO THE NEB PANHANDLE/ ERN
WY...WITH PWS RANGING FROM 1.00 TO NEAR 1.50 INCHES. A FEW STRONG
PULSE STORMS TSTMS MAY FORM NEAR THE BOUNDARY OVER ERN NEB AND WRN
IA THIS AFTN AS SBCAPE APPROACHES 2500 J/KG. OTHER STORMS LIKELY
WILL FORM OVER THE HIGHER TERRAIN OF CNTRL/ERN WY AND MOVE
ESE ALONG FRONTAL ZONE INTO THE LWR PLNS LATER IN THE DAY. THIS
AREA WILL BE ON SRN FRINGE OF THE WLYS...WITH 25-30 KT WNWLY MID LVL
FLOW ATOP ESELY LOW LVL WINDS. COUPLED WITH STEEP MID LVL LAPSE
RATES...SETUP COULD YIELD ISOLD HYBRID MULTI/SUPERCELL STORMS WITH
HAIL/LOCALLY DMGG WIND.
...ND/MN TODAY AND TONIGHT...
WDLY SCTD STORMS MAY FORM THIS AFTN IN NRN MN AND POSSIBLY NRN/ERN
ND IN MODERATE TO STRONG/DEEP CYCLONIC FLOW ON SRN EDGE OF MB UPR
DISTURBANCE. WITH COOL MID LVL TEMPERATURES /MINUS MID TEENS AT
500 MB/...50 F SFC DEWPOINTS...AND 30+ KT MEAN LWR TROPOSPHERIC
FLOW...STORMS COULD PRODUCE ISOLD DMGG WIND AND MARGINALLY SVR HAIL.
LATE TONIGHT AND EARLY THURSDAY...ELEVATED STORMS FORMING IN
STRENGTHENING WAA ZONE ACROSS SRN SK/MB MAY MOVE/DEVELOP ESE INTO
NRN/ERN ND AND NW MN. WHILE SPARSE MOISTURE WILL CONTINUE TO LIMIT
CAPE...MODERATE CLOUD LYR SHEAR AND COOL CLOUD TOP TEMPERATURES
COULD YIELD A THREAT FOR ISOLD SVR HAIL.
...S CNTRL/SE AZ THIS AFTN AND EVE...
NRN SONORA UPR LOW EXPECTED TO DRIFT/WOBBLE MAINLY WNW THROUGH EARLY
THURSDAY. LONG-TERM SATELLITE LOOPS SUGGEST THAT PWS SHOULD
CONTINUE TO SLOWLY INCREASE...OWING TO BOTH WEAK LOW LVL SURGE FROM
THE GULF OF CA AND TO DEEP MOISTENING WITH ADVANCE OF UPR LOW.
EXPECT THAT CONVECTIVE COVERAGE WILL BE MORE WIDESPREAD AND EXTEND
FARTHER WNW THAN YESTERDAY...DESPITE RESIDUAL CLOUDINESS THAT WILL
HINDER LOW LVL DESTABILIZATION. DEGREE OF SVR THREAT WILL DEPEND
LARGELY ON HOW MUCH SFC HEATING OCCURS. GIVEN MODEST UNIDIRECTIONAL
ELY STEERING FLOW...PRIND THAT STORM OUTFLOWS WILL ASSUME SOME
DEGREE OF ORGANIZATION. THUS STORMS COULD POSE A RISK FOR AT LEAST
ISOLD DMGG WIND GUSTS AS THEY PROPAGATE GENERALLY WSW...IN ADDITION
TO HEAVY RAIN.
..CORFIDI.. 07/09/2008
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