SWODY1
SPC AC 211255
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0755 AM CDT FRI MAY 21 2010
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE LOWER OH
VALLEY ACROSS THE TN VALLEY TO THE SOUTH AND SOUTHEAST...
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN WY AND ADJACENT AREAS
OF SD AND NEB SOUTH ACROSS ERN CO AND THE SRN HIGH PLAINS...
...SYNOPSIS...
MID LEVEL FLOW WILL REMAIN QUITE AMPLIFIED ACROSS THE CONUS INTO THE
WEEKEND AS ONE WELL-DEFINED DISTURBANCE MOVES ACROSS THE MIDWEST
THROUGH TODAY AND ANOTHER SUBSTANTIAL TROUGH DEEPENS OVER THE WEST
AND ROCKIES. TRANSIENT RIDGING WILL MOVE FROM THE PLAINS TO THE MS
VALLEY THIS PERIOD.
...CNTRL/SRN HIGH PLAINS...
ANOTHER STRONG SHORT WAVE TROUGH COMING ACROSS THE CA/ORE COAST THIS
MORNING WILL ROTATE THROUGH THE LARGER-SCALE TROUGH ESTABLISHED
ACROSS THE WEST THROUGH TONIGHT. MID LEVEL SWLY FLOW IS FORECAST TO
STRENGTHEN ACROSS ROCKIES AND ADJACENT HIGH PLAINS THROUGH THIS
AFTERNOON AS LEE CYCLOGENESIS OCCURS OVER WY/CO. LOW LEVEL MOISTURE
...CURRENTLY MARGINAL FOR DEEP CONVECTION...WILL INCREASE NWWD AS
PRESSURE FALLS COMMENCE IN EARNEST LATER THIS MORNING AND LOW LEVEL
SELY FLOW STRENGTHENS. COMBINED WITH BOUNDARY LAYER HEATING AND
STEEPENING LAPSE RATES ALOFT...EXPECT A GENERALLY N-S AXIS OF
INSTABILITY TO DEVELOP WITH MLCAPE VALUES RANGING FROM ABOUT 500
J/KG ACROSS SERN WY...TO AS HIGH AS 2000 J/KG OVER PARTS OF TX.
LACK OF STRONGER DESTABILIZATION WITH NWWD EXTENT WILL MOST LIKELY
BE COMPENSATED FOR BY STRONG DYNAMIC FORCING FOR ASCENT WITH THE
APPROACHING SHORT WAVE...AS WELL AS OROGRAPHIC/UPSLOPE FLOW. THESE
INFLUENCES WILL LEAD TO THUNDERSTORM DEVELOPMENT...FIRST OVER THE
HIGHER TERRAIN TO THE WEST...AND THEN SPREADING EAST INTO AXIS OF
MODEST INSTABILITY FROM SERN WY ACROSS NERN CO. PRONOUNCED SPEED
SHEAR...AS WELL AS STRONG DIRECTIONAL SHEAR LOWER IN THE STORM
UPDRAFT WILL LEAD TO ROTATING CELLS CAPABLE OF VERY LARGE HAIL AND
PERHAPS A COUPLE OF TORNADOES.
FARTHER SOUTH ALONG THE DRY LINE...FROM SERN CO TO WEST TX/ERN
NM...STORM INITIATION BECOMES MORE UNCERTAIN. LACK OF STRONGER
HEIGHT FALLS/FORCING AND DEGREE OF CONVECTIVE INHIBITION SUGGEST
THAT STORM DEVELOPMENT WILL BE ISOLATED ALONG THIS AXIS. CONSENSUS
EXISTS AMONG HIGH RESOLUTION MODELS AND THE NAM THAT SURFACE HEATING
AND WEAK BACKGROUND ASCENT MAY BE ADEQUATE FOR AT LEAST A COUPLE OF
STORMS TO INITIATE...ESPECIALLY FROM TX PNHDL SOUTH TO NEAR THE
PECOS RIVER. SHEAR PROFILES WILL BE SUPPORTIVE OF SUPERCELLS AND
LARGE HAIL SHOULD BE THE PRIMARY HAZARD FROM THIS ACTIVITY THAT MAY
DECAY RATHER QUICKLY AFTER DARK.
...SOUTH...
A CORRIDOR OF STRONG HEATING WILL OCCUR ALONG AND SOUTH OF THE
DIFFERENTIAL HEATING ZONE BECOMING ESTABLISHED FROM SRN MS TO SRN GA
AND NORTH FL THIS MORNING. VERY MOIST AIR MASS IN THIS ZONE WILL
CONTRIBUTE TO THE DEVELOPMENT OF STRONG INSTABILITY AND WEAK
INHIBITION. WHILE STRONGER FORCING WITH THE MIDWEST UPPER TROUGH
REMAINS NORTH OF THIS AREA...MID LEVEL WLY FLOW OF 20-30 KT WILL BE
SUFFICIENT FOR SOME STORM ORGANIZATION AND PERHAPS EVEN SUPERCELLS
AS CONVECTION INCREASES THROUGH THE AFTERNOON. LARGE HAIL AND HIGH
WINDS SHOULD BE THE PRIMARY HAZARDS.
THERE IS GREATER UNCERTAINTY OF STORM COVERAGE AND INTENSITY NWD
ACROSS THE TN VALLEY WHERE AIR MASS WILL TAKE LONGER TO RECOVER FROM
MORNING CONVECTION AND CLOUDS. SHEAR WILL BE STRONGER IN THIS REGION
AND EXPECT GREATEST CHANCE FOR STRONG TO SEVERE STORMS MAY BE LATE
AFTERNOON INTO THE EVENING AS LIFT WITH THE COLD FRONT MOVES INTO
THIS AREA FROM THE NORTHWEST.
...MIDWEST...
SOME WEAK DESTABILIZATION AND PERSISTENT BACKGROUND SYNOPTIC SALE
ASCENT APPEARS LIKELY AS UPPER TROUGH SWINGS ACROSS THIS REGION
THROUGH THE DAY. THIS SHOULD CONTRIBUTE TO ONE OR TWO BANDS OF
THUNDERSTORMS SPREADING ACROSS THE REGION FROM ERN IL TO OH. SHEAR
PROFILES ARE NOT PARTICULARLY FAVORABLE FOR SEVERE STORMS.
HOWEVER...COLD AIR ALOFT AND CYCLONIC FLOW REGIME DO SUGGEST THAT A
FEW OF THE STRONGER STORMS MAY BE ACCOMPANIED BY HAIL AND PERHAPS
EVEN A BRIEF TORNADO.
..CARBIN/ROGERS.. 05/21/2010
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