SPC AC 241257
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0757 AM CDT WED JUN 24 2009
VALID 241300Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE NRN PLNS ESE
INTO THE UPR/MID MS VLYS...
...SYNOPSIS...
DOMINANT CNTRL/SRN PLNS UPR RDG WILL REMAIN MORE OR LESS STNRY THIS
PERIOD...BETWEEN UPR LOWS OFF THE MID ATLANTIC AND SRN CA CSTS. THE
WLYS WILL REMAIN CONFINED TO THE PACIFIC NW...NRN RCKYS...NRN
PLNS...AND UPR GRT LKS. WITHIN THE WLYS...SATELLITE SHOWS A WEAK
IMPULSE NOW OVER ERN MT THAT WILL CONTINUE SLOWLY E ACROSS ND/SD
TODAY. THE DISTURBANCE SHOULD TURN ESE TOWARD NRN IL BY THE END OF
THE PERIOD AS UPSTREAM SHORTWAVE RIDGE AMPLIFIES OVER AB/SK AHEAD OF
STRONGER TROUGH NOW APPROACHING VANCOUVER ISLAND.
AT LWR LVLS...PATTERN WILL REMAIN WEAK. WITH TIME...HOWEVER...A
DIFFUSE W-E FRONT NOW EXTENDING E FROM THE SD/NEB BORDER INTO WI
/PARTLY MASKED BY CONVECTIVE OUTFLOW/ WILL BECOME BETTER DEFINED.
IT SHOULD BEGIN TO DRIFT SE AS A WEAK COLD FRONT EARLY THU AS MT UPR
IMPULSE AMPLIFIES ESEWD. FARTHER SW...A WEAK LEE/THERMAL LOW WILL
LINGER OVER THE CNTRL HI PLNS. OUTFLOW BOUNDARIES E OF THE LOW OVER
NEB REGION SHOULD FURTHER WEAKEN TODAY.
...SD/NEB ESE INTO IA AND PARTS OF MN/WI/IL...
TSTMS NOW FORMING OVER NW SD/SW ND LIKELY ARE ELEVATED AND APPEAR TO
BE RELATED TO ASCENT WITH MT UPR IMPULSE. THE STORMS SHOULD DEVELOP
SLOWLY ESE ACROSS THE REMAINDER OF SD THROUGH THE DAY...
AND MAY POSE A THREAT FOR SVR HAIL AND PERHAPS LOCALLY DMGG WIND
WITH TIME AS AMPLE CLOUD LAYER SHEAR/INSTABILITY WILL EXIST FOR
SUSTAINED UPDRAFTS /REF MCD 1298/.
COMBINATION OF SFC HEATING AND PERSISTENT UVV WITH UPR IMPULSE
SUGGESTS THAT THE SD STORMS WILL BECOME SFC-BASED OR NEARLY SO BY
EARLY TO MID AFTN...ESPECIALLY INVOF AFOREMENTIONED FRONT.
PROXIMITY OF WLY MID LVL JET /40 KT DEEP WLY SHEAR/ AND MODERATE
INSTABILITY /SBCAPE AOA 2000 J PER KG/ SHOULD SUPPORT SCTD SUSTAINED
STORMS/SUPERCELLS WITH LARGE HAIL/HIGH WIND. AVAILABILITY OF FAIRLY
RICH LOW LVL MOISTURE AND WEAKLY-BACKED FLOW NEAR/N OF FRONT FURTHER
SUGGEST POTENTIAL FOR A FEW TORNADOES WITH ANY DISCRETE OR
SEMI-DISCRETE STORMS. THE ACTIVITY MAY MERGE INTO A
LOOSELY-ORGANIZED CLUSTER EARLY TONIGHT. THIS CLUSTER SHOULD
MOVE/DEVELOP GENERALLY E ACROSS IA/SRN MN AS MODEST BUT MOIST LLJ
SLIGHTLY STRENGTHENS AND VEERS AHEAD OF AMPLIFYING UPR TROUGH.
FARTHER E AND S...STORM CLUSTERS NOW OVER SE SD...SW MN...AND NW IA
LIKELY ARE BEING SUPPORTED BY ISENTROPIC ASCENT ATOP EARLIER MCS
OUTFLOW...WITH ASCENT ENHANCED BY WEAK WAVE IN SUBTROPICAL BRANCH OF
FLOW /NOW CENTERED OVER ERN NEB/. WHILE MUCH OF THE REGION WAS
CONVECTIVELY OVERTURNED YESTERDAY...SUFFICIENT RECOVERY WILL OCCUR
WITH SFC HEATING TODAY TO SUPPORT INTENSIFICATION OF EXISTING STORMS
AND/OR DEVELOPMENT OF ADDITIONAL ACTIVITY ON OUTFLOW LEFT BY CURRENT
STORMS. WITH AFTN SBCAPE EXPECTED TO BE AOA 3000 J/KG AND PW
REMAINING RATHER HIGH...SOME OF THE STORMS WILL PRODUCE WET
MICROBURSTS AND SVR HAIL DESPITE WEAK SHEAR. SHEAR VECTORS ARE
QUITE VARIABLE ACROSS THE REGION. THUS...STORM CLUSTER MOTION WILL
BE VARIED...BUT SHOULD BE MAINLY E OR ESE INTO PARTS OF SRN MN/SRN
WI/IL...AND PERHAPS S OR SW INTO MO.
...CNTRL GULF CST INTO W CNTRL/S FL...
SCTD DIURNALLY-ENHANCED TSTMS EXPECTED TO STRENGTHEN/REDEVELOP ALONG
WEAK CONFLUENCE AXIS MARKING SW FRINGE OF UPR LOW OFF THE MID
ATLANTIC CST. DESTABILIZATION BENEATH A BELT OF MODEST... LARGELY
UNIDIRECTIONAL NLY/ENELY FLOW MAY SUPPORT ORGANIZATION OF ACTIVITY
INTO SMALL MULTICELL CLUSTERS. THESE COULD YIELD ISOLD LOCALLY DMGG
WIND AND PERHAPS A SPOT OR TWO OF HAIL THROUGH EARLY THIS EVE.
..CORFIDI/GRAMS.. 06/24/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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