SWODY2
SPC AC 261730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT FRI JUN 26 2009
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM WRN GREAT LAKES THROUGH
LOWER MO VALLEY TO SRN KS/NRN OK...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE DAKOTAS
INTO FAR WRN MN...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS COASTAL CAROLINAS...
...SYNOPSIS...
SHORTWAVE TROUGH...CURRENTLY OVER WRN CANADA/NWRN U.S. IS FORECAST
TO AMPLIFY ESEWD ACROSS THE NRN PLAINS/UPPER MS VALLEY SATURDAY
ACCOMPANIED BY A COLD FRONT. AN IMPULSE CURRENTLY OVER THE SWRN
U.S. WILL EJECT NEWD OVER TOP OF UPPER RIDGE JUST AHEAD OF THIS
FEATURE. EARLY SATURDAY THE FRONT WILL EXTEND FROM A WEAK
SURFACE LOW IN MN SWWD THROUGH ERN NEB INTO SWRN KS THEN ADVANCE TO
A POSITION FROM MI SWWD INTO THE SRN PLAINS BY THE END OF THE
PERIOD. MEANWHILE...UPPER LOW...CURRENTLY OVER SRN ONTARIO...IS
FORECAST TO MOVE SEWD THROUGH NEW ENGLAND...DRIVING A COLD FRONT OFF
THE THE CAROLINA SEABOARD SATURDAY NIGHT. THE WRN PORTIONS OF THIS
BOUNDARY WILL LIFT NWD THROUGH THE MID MS VALLEY AS A WARM FRONT.
...WRN GREAT LAKES SWWD THRU MID MS VALLEY TO CENTRAL/SRN PLAINS...
AT 12Z SATURDAY...STORMS SHOULD BE ONGOING IN ASSOCIATION WITH LEAD
IMPULSE NORTH OF WARM FRONT WITHIN ZONE OF WARM ADVECTION AND
ISENTROPIC LIFT OVER THE UPPER MS VALLEY REGION. ACTIVITY WILL
LIKELY BE ELEVATED AND EMBEDDED WITHIN STRONG VERTICAL SHEAR...BUT
LIMITED INSTABILITY SUGGESTS ANY SEVERE THREAT SHOULD BE MINIMAL.
A RESERVOIR OF MID-UPPER 60S DEWPOINTS WILL EXIST SOUTH OF WARM
FRONT. AS THE MOIST BOUNDARY LAYER WARMS...THE ATMOSPHERE WILL
LIKELY BECOME MODERATELY UNSTABLE IN ADVANCE OF THE COLD FRONT.
PRIMARY LOW LEVEL JET IS FORECAST TO SHIFT ENEWD ACROSS THE WRN
GREAT LAKES DURING THE DAY...WITH WEAKENING AND VEERING BOUNDARY
LAYER FLOW IN WARM SECTOR. HOWEVER...STRENGTHENING MID-UPPER FLOW
IN ASSOCIATION WITH AMPLIFYING UPPER TROUGH WILL MAINTAIN 30-40 KT
BULK SHEAR OVER MID-UPPER MS VALLEY PORTION OF WARM SECTOR DESPITE
WEAKENING/VEERING LOW LEVEL WINDS. STORMS WILL REDEVELOP ALONG AND
AHEAD OF COLD FRONT AS THE BOUNDARY LAYER DESTABILIZES SATURDAY
AFTERNOON...LIKELY EVOLVING INTO SUPERCELLS AND BOWING SEGMENTS.
DAMAGING WIND AND ISOLATED HAIL WILL BE THE MAIN THREATS.
FARTHER SW /I-70 IN MO TO NRN OK/TX PANHANDLE/...MODELS SUGGEST
WEAKER MID/UPPER LEVEL FORCING FOR ASCENT ACROSS THESE AREAS AS SRN
EXTENT OF NORTH CENTRAL STATES SHORT WAVE TROUGH MOVES ESEWD AND
WEAK IMPULSES FROM SWRN STATES TRACK INTO THE CENTRAL PLAINS.
THUS...GIVEN WEAKER FORCING ALOFT...STRONGER SURFACE HEATING WILL BE
NEEDED TO WEAKEN THE CAP ALONG THE SRN EXTENT OF THE SURFACE FRONT
WITH TSTMS EXPECTED TO DEVELOP BY LATE AFTERNOON...OR MORE LIKELY BY
EARLY EVENING.
TSTMS SHOULD CONTINUE SATURDAY NIGHT AS THE FRONT MOVES S/SEWD
TOWARD THE OZARKS...RED RIVER VALLEY AND W TX...BUT WILL TEND TO
WEAKEN IN SEVERITY AS INSTABILITY WANES WITH THE ONSET OF BOUNDARY
LAYER COOLING. ACTIVITY SHOULD TEND TO BE MORE POST FRONTAL WITH
WAA REGIME ALONG NOSE OF 30 KT SLY LLJ EXTENDING INTO THE TX
PANHANDLE/WRN OK SATURDAY NIGHT SUPPORTING A GREATER LIKELIHOOD FOR
MORE SUSTAINED ELEVATED TSTMS. STRONGER EFFECTIVE SHEAR ACROSS NW
TX/WRN OK SUGGESTS ELEVATED TSTMS COULD BE ORGANIZED AT TIMES WITH A
THREAT FOR ISOLATED HAIL.
...DAKOTAS/WRN MN...
STRONG FORCING FOR ASCENT ATTENDANT TO AMPLIFYING UPPER TROUGH
ACROSS THIS REGION ON SATURDAY AND WITHIN EXIT REGION OF
ACCOMPANYING 60-70 KT MID LEVEL JET WILL SUPPORT TSTM DEVELOPMENT
ACROSS MUCH OF ND INTO NRN SD AND THEN WRN MN BY LATE AFTERNOON/
EVENING. DESPITE SURFACE HEATING AND STEEP LOW AND MID LEVEL LAPSE
RATES...SURFACE DEWPOINTS IN THE UPPER 40-MID 50S WILL TEND TO LIMIT
THE DEVELOPMENT OF STRONGER INSTABILITY. HOWEVER...THE STRONG
FORCING FOR ASCENT AND STEEP LAPSE RATE ENVIRONMENT/COOLING MID
LEVEL TEMPERATURES /-18 C AT 500 MB/ WILL SUPPORT A THREAT FOR
HAIL...SOME POSSIBLY LARGE. EFFECTIVE BULK SHEAR AROUND 25 KT
SUGGESTS ACTIVITY WILL TEND TO BE MULTICELLULAR WITH STRONG WIND
GUSTS ALSO A THREAT.
...ERN CAROLINAS...
STRONG SURFACE HEATING WITHIN A MOIST/PRE-FRONTAL AIR MASS AND WEST
OF THE SEA BREEZE IS EXPECTED TO SUPPORT A MODERATELY UNSTABLE AIR
MASS...DESPITE WEAK MID LEVEL LAPSE RATES. FORCING FOR ASCENT
SPREADING SEWD ACROSS THIS REGION BY LATE SATURDAY AFTERNOON IS
EXPECTED TO SUPPORT TSTM DEVELOPMENT...ESPECIALLY WITH LOW LEVEL
CONVERGENCE INCREASING AS THE COLD FRONT MERGES WITH THE SEA BREEZE.
INCREASING NWLY FLOW ALOFT WILL SUPPORT EFFECTIVE BULK SHEAR
SUFFICIENT FOR ORGANIZED STORMS AND A SEWD STORM MOTION. DAMAGING
WINDS AND MARGINALLY SEVERE HAIL SHOULD BE THE PRIMARY THREATS.
..PETERS.. 06/26/2009
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