SWODY1
SPC AC 091250
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT MON MAY 09 2011
VALID 091300Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF ERN WY...NWRN
NEB INTO PARTS OF THE DAKOTAS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE MID MS AND OH
VALLEYS...
...NRN HIGH PLAINS...
MIDLEVEL VORTICITY MAXIMUM AND ASSOCIATED JET STEAK CURRENTLY
ROUNDING LARGE-SCALE TROUGH BASE OVER THE LOWER CO VALLEY WILL
TRANSLATE NNEWD THROUGH THE CNTRL ROCKIES TODAY INTO THE NRN HIGH
PLAINS BY TONIGHT. IN THE LOW LEVELS...SURFACE LOW CURRENTLY OVER
WRN NEB MAY DRIFT INTO N-CNTRL NEB BY AFTERNOON WITH SECONDARY
CYCLONE DEVELOPMENT FORECAST OVER NERN CO. THIS SECONDARY LOW WILL
THEN DEVELOP NEWD TO CNTRL OR ERN SD BY 10/12Z WHILE ASSOCIATED WARM
FRONT SLOWLY PIVOTS NWD/NEWD THROUGH THE MID MO VALLEY.
WHILE SURFACE DEWPOINTS WILL INCREASE ALONG AND IMMEDIATELY N OF
WARM FRONT OVER CNTRL/ERN SD...A RELATIVELY COOL AND COMPARATIVELY
DRIER BOUNDARY LAYER WILL BE MAINTAINED ON BACKSIDE OF PRIMARY
SURFACE LOW OVER ERN WY/WRN SD. NONETHELESS...THE PRESENCE OF STEEP
MIDLEVEL LAPSE RATES /SEE 12Z RAP SOUNDING/ AND 850 MB DEWPOINTS OF
10-12 C WRAPPING AROUND SURFACE LOW WILL SUPPORT MODERATE ELEVATED
INSTABILITY LATER TODAY WITH MUCAPE VALUES APPROACHING 1000-2000
J/KG.
LOW-LEVEL UPSLOPE FLOW COUPLED WITH INCREASING DCVA IN ADVANCE OF
MIDLEVEL IMPULSE ARE EXPECTED TO FOSTER SCATTERED TSTMS BY AFTERNOON
ACROSS ERN WY...THE NEB PNHDL AND WRN SD WITHIN A KINEMATIC
ENVIRONMENT FEATURING 40-50 KT OF DEEP SLY SHEAR. WHILE THERE IS
SOME QUESTION WHETHER STORMS WILL BE TRULY SURFACE BASED...GIVEN
SETUP WILL STILL BE SUPPORTIVE OF SUPERCELLS CAPABLE OF MAINLY
SEVERE HAIL. EXPECT THE HAIL THREAT TO SPREAD NWD/NEWD INTO CNTRL
SD AND SRN PARTS OF ND OVERNIGHT WITHIN INTENSIFYING LOW-LEVEL WAA
REGIME.
...MID MS/OH VALLEYS...
CONVECTIVE EVOLUTION REMAINS MORE UNCERTAIN DUE TO PROXIMITY OF
REGION TO MIDLEVEL RIDGE AXIS. MORNING WATER VAPOR IMAGERY DOES
SUGGEST THE PRESENCE OF A WEAK SHORT WAVE TROUGH MOVING THROUGH
NEB/KS/OK WITH FORCING FOR ASCENT ASSOCIATED WITH THIS FEATURE
LIKELY CONTRIBUTING TO ONGOING ELEVATED STORMS OVER MO. DOWNSHEAR
/SEWD/ EXPANSION OF CIRRUS CANOPY ATTENDANT TO THESE STORMS WILL
TEMPER DAYTIME HEATING ALONG WARM FRONT SLOWLY LIFTING NWD.
STILL...THE PRESENCE OF BOUNDARY LAYER DEWPOINTS IN THE 60S AND DRY
ADIABATIC MIDLEVEL LAPSE RATES /REF. 12Z SGF AND TOP SOUNDINGS/ WILL
CONTRIBUTE TO AFTERNOON MLCAPE VALUES APPROACHING 3000-4000+ J/KG
ALONG AND W OF NW-SE ORIENTED WARM FRONT.
ONGOING ELEVATED STORMS ACROSS MO WILL BE CAPABLE OF ISOLATED
OCCURRENCES OF HAIL THROUGH THE MORNING GIVEN THE VERY STEEP
MIDLEVEL LAPSE RATES ALREADY IN PLACE. THE ONSET OF DIABATIC
WARMING MAY ALLOW THESE STORMS TO BECOME ROOTED IN THE DESTABILIZING
BOUNDARY LAYER THIS AFTERNOON OVER ERN MO/WRN IL WITH ACTIVITY
GROWING UPSCALE INTO A SEWD-MOVING MCS CAPABLE OF DAMAGING WINDS AND
HAIL. ADDITIONAL MORE ELEVATED STORMS CAPABLE OF HAIL APPEAR LIKELY
TO DEVELOP TONIGHT AS WAA AND ISENTROPIC ASCENT ARE ENHANCED IN EXIT
REGION OF NOCTURNAL LLJ.
...TX...
A HOT AND DEEPLY MIXED BOUNDARY LAYER IS EXPECTED TO ONCE AGAIN
DEVELOP TODAY INVOF DRYLINE. ALSO SIMILAR TO YESTERDAY...MODEL
GUIDANCE /AND TO SOME DEGREE WATER VAPOR IMAGERY/ SUGGESTS THAT A
LOW-LATITUDE IMPULSE WILL PROGRESS EWD FROM NWRN MEXICO INTO WRN TX
BY AFTERNOON. DEEP-LAYER VERTICAL SHEAR WILL REMAIN ON THE MARGINS
OF THAT SUPPORTIVE OF ORGANIZED UPDRAFTS /30 KT/. HOWEVER...THE
PRESENCE OF STEEP LOW TO MIDLEVEL LAPSE RATES AND 2000-3000 J/KG
MLCAPE WILL FOSTER STRONG UPDRAFTS CAPABLE OF HAIL AND LOCALLY
DAMAGING WINDS. ANY STORMS THAT DEVELOP SHOULD REMAIN RATHER
ISOLATED AND DISSIPATE BY EVENING AS THE BOUNDARY LAYER COOLS AND
THE CONVECTIVE INHIBITION INCREASES.
..MEAD/GRAMS.. 05/09/2011
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