SPC AC 121959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT TUE MAY 12 2009
VALID 122000Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL/SRN HIGH
PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN CENTRAL PLAINS EWD
INTO THE MID MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS IN CENTRAL/SRN FL PENINSULA...
...CENTRAL/SRN HIGH PLAINS...
WARM FRONT WAS LIFTING RAPIDLY NWD THROUGH THE TX PANHANDLE/SWRN OK
WITH CLEARING SKIES AND WARMING TEMPERATURES. UPPER WV IN FAR SWRN
TX HAS INITIATED CONVECTION OVER SERN NM AND EXPECT STORMS WILL
DEVELOP/SPREAD NEWD INTO WRN TX THIS AFTERNOON/EVENING. OTHER HIGH
BASED STORMS MAY SPREAD INTO ERN CO/WRN KS THIS AFTERNOON FROM CO
HIGHER TERRAIN. ONCE STORMS MOVE INTO MORE MOIST BOUNDARY LAYER...
DEWPOINTS IN THE 50S AND LOWER 60S...MUCAPES AROUND 3000 J/KG SHOULD
BE SUPPORTIVE OF SUPERCELLS WITH HAIL/WIND THREAT. STORMS MAY
STRUGGLE TO MOVE VERY FAR EWD INTO KS/OK WHERE CLOUDS/COOLER
TEMPERATURES WILL PERSIST THROUGH THE LATE AFTERNOON HOURS.
...CENTRAL/SRN FL PENINSULA...
DESPITE VERY WEAK ENVIRONMENTAL WINDS...THE COMBINATION OF SWD
MOVING COLD FRONT...MLCAPES AROUND 3000 J/KG AND 500 MB TEMPERATURES
AT -10 TO -11C WILL BE FAVORABLE FOR STORMS WITH HAIL/WIND DAMAGE
UNTIL ABOUT 00Z. A SLIGHT RISK HAS BEEN ADDED TO THE AREA.
...IL...
STRONG LOW LEVEL WARM ADVECTION...CURRENTLY MAINTAINING CONVECTION
FROM NERN AR NWD INTO ERN NEB...WILL SPREAD NEWD THROUGH THE PERIOD
AND STRENGTHEN TONIGHT AS LOW LEVEL JET SPEEDS INCREASE TO 50-60 KT.
EXPANDED THE SLIGHT RISK NEWD INTO IL FOR TONIGHT AS FORECAST
SOUNDINGS INDICATE MUCAPES FROM 1000-1500 J/KG AND EFFECTIVE SHEAR
AT 40-50 KT...WHICH WOULD BE FAVORABLE FOR HAIL.
...SRN NEW ENGLAND...
STRONGER CONVECTION HAS WEAKENED AS DRIER AIR AS MOVED INTO THE
REGION...WHICH SHOULD END EARLIER THREAT FOR BRIEF SEVERE WEATHER.
...SRN AR/NERN LA/WRN MS...
BAND OF STORMS WERE MOVING SEWD ALONG INSTABILITY AXIS TOWARD NERN
LA/WRN MS. THOUGH ISOLATED WIND/HAIL THREAT IS POSSIBLE...
RELATIVELY WEAK SHEAR AND WEAK LOW LEVEL JET INDICATE HEAVY RAINS
WOULD BE THE PRIMARY THREAT.
..IMY.. 05/12/2009
.PREV DISCUSSION... /ISSUED 1203 PM CDT TUE MAY 12 2009/
CORRECTED PROBABILITY GRAPHIC POINTS
...SYNOPSIS...
VIGOROUS UPPER TROUGH AND ASSOCIATED STRONG POLAR JET DRIVES EWD
ACROSS NRN ROCKIES THIS AFTERNOON TO DAKOTAS TONIGHT. RAPIDLY
DEVELOPING SURFACE LOW THIS AFTERNOON WRN DAKOTAS...DEEPENS NEWD
INTO SRN MANITOBA BY 12Z THU AS STRONG COLD FRONT CURRENTLY CENTRAL
MT INTO SRN IDAHO SWEEPS EWD INTO NRN HIGH PLAINS BY THIS EVENING.
SHARPENING LEE TROUGH HIGH PLAINS WILL MAINTAIN A RAPID RETURN OF
THE SRN PLAINS MOISTURE NWD THRU THE PERIOD. AN EML WITH LAPSE
RATES GENERALLY 8C/KM HAS OVERSPREAD MUCH OF THE PLAINS AND WITH THE
RETURN OF GULF MOISTURE INSTABILITY WILL BE ON THE INCREASE THRU THE
PERIOD E OF DRY LINE AS WARM FRONT CURRENTLY NEAR RED RIVER LIFTS
NWD THRU OK THIS AFTERNOON.
...NRN/CENTRAL PLAINS...
STRONG SHEAR AND STEEP LAPSE RATES WILL ACCOMPANY TROUGH AND COLD
FRONT INTO NRN HI PLAINS BY THIS EVENING. MOISTURE AND INSTABILITY
IS VERY LIMITED...HOWEVER GIVEN THE STRONG KINEMATICS AND LAPSE
RATES...THUNDERSTORMS SHOULD DEVELOP ALONG/AHEAD OF COLD FRONT THIS
AFTERNOON SERN MT/NERN WY WHICH WILL PROVIDE A RISK OF PRIMARILY
DAMAGING WINDS AND HAIL. DURING THE EVENING A LINE OF THUNDERSTORMS
SHOULD INCREASE IN SEVERE POTENTIAL AS THEY ENCOUNTER THE MORE
FAVORABLE THERMODYNAMIC ENVIRONMENT WHICH WILL BE DEVELOPING THIS
AFTERNOON ALONG THE LOW LEVEL JET IN THE DAKOTAS. A SQUALL LINE
WILL MOVE RAPIDLY NEWD AHEAD OF DEEPENING SURFACE LOW ACROSS ND/SD
TONIGHT WITH PRIMARILY A WIND DAMAGE THREAT.
AT LEAST ISOLATED SEVERE WILL BE POSSIBLE SWD ALONG THE DRY LINE TO
WRN NEB WHERE COMBINATION OF VERY STEEP LAPSE RATES 40KT OF BULK
SHEAR AND MLCAPE FROM 500-1000 J/KG WILL BE IN PLACE BY MAX HEATING.
STORMS WILL HAVE A DIFFICULT TIME CONTINUING SEVERE MOVING E OF DRY
LINE GIVEN THE EXPECTED REMAINING CAP.
...SRN HIGH PLAINS...
DRY LINE WILL MIX EWD INTO SWRN KS SWD THRU CENTRAL TX PANHANDLE TO
E OF DAVIS MTS BY MID AFTERNOON. DEWPOINTS AOA 60F WILL CONTINUE
SPREADING NWD E OF DRY LINE THRU THE AFTERNOON ALONG THE WRN OK/TX
BORDER. WITH ADIABATIC LAPSE RATES IN PLACE BY MAX HEATING ALONG/W
OF DRY LINE...AIR MASS BECOMES STRONGLY UNSTABLE AT LEAST AS FAR N
AS ERN TX PANHANDLE E OF DRY LINE. A WEAK BUT WELL DEFINED MID
LEVEL VORT NOTED ON W/V IMAGERY NOW ENTERING FAR SWRN TX COULD BE A
FACTOR IN PROVIDING SOME ENHANCED LIFT AND SHEAR ACROSS DRY LINE
ABOUT TIME OF MAX HEATING. AT LEAST ISOLATED SEVERE THUNDERSTORMS
COULD DEVELOP ALONG AND JUST E OF DRY LINE BY LATE AFTERNOON SWD TO
BIG BEND. PRIMARY RISK WILL BE VERY LARGE HAIL AND DOWNBURST WINDS
WITH ANY STORM THAT DEVELOPS...AS GIVEN THE 3000 J/KG OR GREATER OF
MLCAPE...SUPERCELLS ARE EXPECTED. ISOLATED TORNADOES ALSO
POSSIBLE...PARTICULARLY IN THE AREA OF ENHANCED LOW LEVEL SHEAR
WHERE THE INTERSECTION OF RETURNING WARM FRONT AND DRY LINE ERN TX
PANHANDLE.
...OK/KS/MO/IA...
AMPLE LOW LEVEL MOISTURE IS IN PLACE THIS MORNING OVER MUCH OF TX.
THIS AIRMASS IS SPREADING NORTHWARD ON A 40-50 KT 850MB JET THROUGH
THE DAY FROM OK INTO KS AND EVENTUALLY IA/MO ABOVE THE SHALLOW WARM
FRONTAL SURFACE. ELEVATED INSTABILITY WITH MUCAPES TO 2000 J/KG WILL
CONTINUE TO SUPPORT A RISK OF LARGE HAIL NOW OCCURRING OVER OK AND
SRN KS.
...SRN NEW ENGLAND...
WITH POTENTIAL FOR SBCAPE UP TO 500 J/KG AND A STEEP LAPSE RATE
ENVIRONMENT...SOME HAIL MAY BE POSSIBLE. WEAK LOW TO MID
TROPOSPHERIC FLOW WILL LIKELY KEEP THE HAIL THREAT MARGINAL/SPORADIC
IN NATURE...AND ANY SUCH THREAT WILL QUICKLY WANE AFTER DARK.
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