SPC AC 251257
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0757 AM CDT THU JUN 25 2009
VALID 251300Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID MS VLY ENE TO THE
LWR GRT LKS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER WRN PARTS OF THE CNTRL
PLNS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF CNTRL AND NRN
MT...
...SYNOPSIS...
DOMINANT UPR RDG WILL REMAIN OVER THE SRN/CNTRL PLNS THROUGH FRI.
IN THE WAKE OF AMPLIFYING TROUGH NOW OVER THE UPR GRT LKS...AND
DOWNSTREAM FROM TROUGH NOW OVER BC/WA...EXPECT THE RDG TO
TEMPORARILY BUILD N ACROSS THE NRN PLNS. ON THE IMMEDIATE NE SIDE
OF THE RDG...WEAK IMPULSE THAT CROSSED THE DAKOTAS YESTERDAY IS NOW
OVER IA. THIS FEATURE SHOULD TURN MORE SSE TODAY AND REACH THE LWR
OH/LWR TN VLY TONIGHT. IN THE WEST...BC/WA TROUGH APPEARS TO HAVE
DISLODGED LONG-LIVED LOW OFF THE SRN CA CST. THE CA LOW SHOULD MOVE
ACROSS CNTRL/SRN CA LATER TODAY...AND SHEAR NE ACROSS THE GRT BASIN
TONIGHT/EARLY FRI.
WITH THE PRIMARY BELT OF THE WLYS REMAINING IN CANADA...FEATURES AT
LWR LVLS WILL REMAIN FAIRLY WEAK ACROSS THE U.S. TWO DIFFUSE
CONFLUENCE AXES ARE APPARENT ATTM OVER THE N CNTRL STATES...
EXTENDING FROM SRN MN/IA/WI/NRN IL ENE INTO WRN QUEBEC. THESE
FEATURES ARE LOOSELY ASSOCIATED WITH UPR GRT LKS UPR TROUGH AND
SHOULD MOVE GENERALLY ESE THROUGH THE PERIOD. THE WRN PARTS OF
THESE BOUNDARIES WILL REDEVELOP N AS A WEAK WARM FRONT ACROSS CNTRL
NEB AND THE WRN DAKOTAS LATER TODAY AS A FAIRLY WELL-DEFINED FRONTAL
SYSTEM EVOLVES OVER THE NRN RCKYS/NRN HI PLNS AHEAD OF BC/WA
IMPULSE.
...MID MS VLY ENE TO THE LWR GRT LKS...
AFOREMENTIONED LOW LVL CONFLUENCE AXES/WEAK COLD FRONTS LIKELY WILL
SERVE TO FOCUS DIURNALLY-ENHANCED STORM DEVELOPMENT. BECAUSE
CONVERGENCE ALONG THESE FEATURES WILL BE WEAK AND PARTLY DISRUPTED
BY OUTFLOW FROM PREVIOUS CONVECTIVE SYSTEMS...AND BECAUSE THE
STRONGEST LARGE SCALE FORCING FOR ASCENT WILL REMAIN IN CANADA...
STORM DEVELOPMENT MAY BEGIN SOMEWHAT HAPHAZARDLY AS SFC HEATING
IRREGULARLY DESTABILIZES THE REGION. BY MID TO LATE AFTN...HOWEVER
...EXPECT THAT SEVERAL LOOSELY-ORGANIZED CLUSTERS OF STORMS WILL
HAVE EVOLVED FROM PARTS OF ERN IA/IL AND SRN WI E INTO PARTS OF
IND...LWR MI...OH...NW PA AND WRN NY.
AMPLE INSTABILITY WILL EXIST FOR STORMS WITH SVR HAIL/WIND...
ESPECIALLY FROM IA/IL/MO INTO SRN MI/OH...WHERE SBCAPE SHOULD BE AOA
3000 J/KG. STRONGER MEAN FLOW AND FORCING FOR ASCENT SHOULD
COMPENSATE TO SUPPORT LONG-LIVED/POSSIBLY ROTATING UPDRAFTS FARTHER
N/E ACROSS MI/SRN ONTARIO AND NY.
PERSISTENT FORCING FOR ASCENT /PARTICULARLY UPR DIVERGENCE/ AND
STRENGTHENING WSWLY LOW LVL FLOW ASSOCIATED WITH AMPLIFYING UPR
TROUGH SUGGEST THAT SOME OF THE STORMS/STORM CLUSTERS WILL REMAIN
ACTIVE INTO TONIGHT OVER PARTS OF NY/PA.
FARTHER SW...A SEPARATE...MORE DIURNAL CLUSTER OF STORMS MAY EVOLVE
OVER MO...IN ASSOCIATION WITH IMPULSE NOW IN IA. WIND AND STABILITY
FIELDS SUGGEST THAT SUCH A CLUSTER...WERE IT TO FORM...SHOULD MOVE
MAINLY SSEWD. EMBEDDED STORMS COULD YIELD A FEW SPOTS OF SVR
WIND/HAIL GIVEN HI PWS AND STRONG SFC HEATING EXPECTED.
...WRN PARTS OF THE CNTRL PLNS...
LOW LVL WAA SHOULD INCREASE OVER WRN PARTS OF THE CNTRL/NRN PLNS
LATER TODAY THROUGH TONIGHT AS WEAK WARM FRONT REDEVELOPS NWD AHEAD
OF APPROACHING UPR TROUGH. CURRENT WV IMAGERY IN THE REGION
PROVIDES MIXED SIGNALS REGARDING POTENTIAL FOR SVR STORM
DEVELOPMENT. VARIOUS WEAK DISTURBANCES ARE APPARENT IN BAND OF FLOW
ON WRN FRINGE OF UPR RDG...BUT HEIGHTS MAY RISE SLIGHTLY AHEAD OF
BC/WA TROUGH.
NEVERTHELESS...GIVEN MOISTURE ALREADY PRESENT OVER REGION AND THE
LIKELIHOOD FOR STRONG SFC HEATING/DEVELOPMENT OF TERRAIN INDUCED
CIRCULATIONS TODAY...IT SEEMS THAT A CONDITIONAL RISK FOR SVR
AFTN/EVE WILL EXIST FROM NE CO/SE WY INTO WRN NEB AND PERHAPS SW SD.
GIVEN 25+ KT DEEP WLY SHEAR AND STRENGTHENING SLY LLJ...SOME OF THE
STORMS MAY EVOLVE INTO A SMALL CLUSTER OR TWO THIS EVE...MOST LIKELY
IN NEB. THIS ACTIVITY MAY YIELD A CONTINUING THREAT FOR DMGG WIND
AND POSSIBLY HAIL THROUGH EARLY FRI.
...MT...
STRENGTHENING COLD FRONT ASSOCIATED WITH BC/WA TROUGH WILL MOVE ESE
ACROSS CNTRL MT TODAY/TONIGHT. ALTHOUGH LOW LVL MOISTURE WILL BE
SPARSE...STEEP LOW TO MID LVL LAPSE RATES...INCREASING
CONVERGENCE/FRONTAL ASCENT...AND DPVA SUGGEST A GOOD CHANCE FOR
STORM DEVELOPMENT ALONG FRONT LATE THIS AFTN/EARLY TONIGHT. LARGE
TEMPERATURE-DEW POINT SPREADS AND FAIRLY STRONG BACKGROUND WIND
FIELD /40-50 KT WSW FLOW AT 500 MB/ COULD YIELD A THREAT FOR A FEW
SVR WIND GUSTS AND POSSIBLY SVR HAIL.
..CORFIDI/GRAMS.. 06/25/2009
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