Monday, March 23, 2009

DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 230530
SWODY2
SPC AC 230527

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 AM CDT MON MAR 23 2009

VALID 241200Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN PARTS OF OK/TX INTO
THE LOWER MS VALLEY...

...SYNOPSIS...

MID/UPPER-LEVEL LOW INITIALLY OVER SD/NEB WILL EVOLVE INTO AN OPEN
WAVE TUESDAY AS NEXT UPSTREAM VORTICITY MAXIMUM/JET STREAK
TRANSLATES EWD THROUGH THE CNTRL/SRN PLAINS EVENTUALLY INTO THE MID
MS VALLEY. AS THIS OCCURS...BROADER-SCALE TROUGH WILL BECOME
NEGATIVELY-TILTED WITH THE MOST NOTABLE HEIGHT FALLS/DYNAMIC FORCING
FOR ASCENT SHIFTING EWD THROUGH THE MID/LOWER MO VALLEYS AND OZARK
PLATEAU INTO THE UPPER MIDWEST AND MID MS VALLEY.

AT THE SURFACE...OCCLUDED SURFACE LOW INITIALLY OVER ERN SD WILL
DEVELOP ENEWD THROUGH CNTRL MN...NWRN WI TO LAKE SUPERIOR. TRAILING
COLD FRONT WILL MOVE EWD/SEWD THROUGH THE PERIOD...LIKELY EXTENDING
FROM SURFACE LOW OVER CNTRL MN SWD THROUGH CNTRL MO AND THEN MORE
SSWWD THROUGH THE ARKLATEX INTO THE TX HILL COUNTRY BY 24/21Z. A
WEAK WARM OR MARINE FRONT WILL CONCURRENTLY LIFT NWD THROUGH THE
LOWER MS VALLEY IN ADVANCE OF THE COLD FRONT.

...ERN PARTS OF OK/TX INTO THE MIDDLE AND LOWER MS VALLEYS...

PERSISTENT LOW-LEVEL RIDGING ALONG THE E COAST /IN THE WAKE OF
DEEP-LAYER CYCLONE OVER THE WRN ATLANTIC/ WILL CONTINUE TO LIMIT THE
BREADTH OF PREFRONTAL WARM SECTOR...PARTICULARLY OVER THE MID MS
VALLEY INTO UPPER MIDWEST. FARTHER S...AIR MASS WILL CONTINUE TO
MODIFY OVER THE WRN GULF BASIN WITH DEWPOINTS GRADUALLY INCREASING
INTO THE 60S AHEAD OF COLD FRONT FROM ERN TX INTO THE LOWER MS
VALLEY. THIS MOISTURE WILL COINCIDE WITH MODESTLY STEEP MIDLEVEL
LAPSE RATES...CONTRIBUTING TO POCKETS OF MODERATE CONVECTIVE
INSTABILITY ACROSS THE SLIGHT RISK AREA WHERE MLCAPE MAY APPROACH
1000 J/KG. MORE WIDESPREAD CLOUDINESS AND DRIER BOUNDARY LAYER
CONDITIONS WILL LIMIT MLCAPE TO AOB 500 J/KG FROM THE OZARK PLATEAU
INTO MID MS VALLEY.

CLUSTERS OR A BROKEN LINE OF TSTMS WILL LIKELY BE ONGOING ALONG
FRONT TUESDAY MORNING FROM THE LOWER MO VALLEY INTO NRN TX. ZONE OF
DEEP ASCENT ASSOCIATED WITH SECONDARY VORTICITY MAXIMUM/JET STREAK
WILL GRADUALLY OVERSPREAD FRONTAL ZONE...CONTRIBUTING TO A STEADY
INCREASE IN STORM INTENSITY THROUGH THE DAY. DESPITE THIS INCREASED
FORCING AND VERY STRONG WIND FIELDS...THE DEGREE OF STORM
ORGANIZATION/SUSTENANCE REMAINS IN QUESTION OVER THE OZARK PLATEAU
INTO THE MID MS VALLEY DUE TO THE VERY MARGINAL INSTABILITY.
THEREFORE...ONLY LOW SEVERE PROBABILITIES WILL BE MAINTAINED IN THIS
FORECAST.

ONLY A GLANCING INFLUENCE OF ABOVE-MENTIONED SECONDARY IMPULSE WILL
RESULT IN LARGE-SCALE FORCING DECREASING WITH SWD EXTENT ACROSS THE
SLIGHT RISK AREA. NONETHELESS...CONVERGENCE ALONG THE FRONT AND A
GENERALLY WEAK CAP ACROSS PRE-FRONTAL WARM SECTOR SHOULD ALLOW FOR
VIGOROUS TSTM DEVELOPMENT BY AFTERNOON AS BOUNDARY LAYER
WARMS/DESTABILIZES. THE COMBINATION OF 50-60 KT SWLY MIDLEVEL FLOW
AND SRN EXTENSION OF 45-55 KT SLY LLJ WILL RESULT IN VERTICAL SHEAR
PROFILES MORE THAN SUFFICIENT FOR EMBEDDED SUPERCELL STRUCTURES.
DAMAGING WIND GUSTS AND HAIL WILL BE THE PRIMARY SEVERE WEATHER
THREATS THOUGH TORNADOES ARE POSSIBLE WITH ANY MORE INTENSE AND
LONGER-LIVED SUPERCELLS THAT MAY DEVELOP.

...UPPER MS VALLEY...

PROVIDED SOME DIABATIC HEATING INVOF OCCLUDED SURFACE LOW...SETUP
WILL BE FAVORABLE FOR THE DEVELOPMENT OF LOW-TOPPED TSTMS TUESDAY.
VERTICAL SHEAR WILL NOT BE STRONG OWING TO THE CLOSE PROXIMITY TO
DEEP-LAYER LOW CENTER. HOWEVER...GIVEN THAT LAPSE RATES WILL BE
STEEP AND THERMODYNAMIC PROFILES RATHER COOL...ENVIRONMENT WILL BE
SUPPORTIVE OF HAIL WITH ANY MORE INTENSE TSTMS.

..MEAD.. 03/23/2009

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