SWODY1
SPC AC 211934
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0234 PM CDT MON SEP 21 2009
VALID 212000Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN INTO EARLY TONIGHT
FROM SW MO ACROSS OK INTO N TX...
...20Z UPDATE...
...CNTRL/SRN PLAINS...
MODELS ARE SUGGESTIVE THAT STRONGEST HIGH-LEVEL DIVERGENCE WILL
REMAIN GENERALLY FOCUSED ACROSS EASTERN PORTIONS OF THE CENTRAL
PLAINS THROUGH MUCH OF THE REMAINDER OF THE PERIOD. AS A VIGOROUS
SHORT WAVE IMPULSE CONTINUES TO DIG NEAR OR TO THE LEE OF THE
SOUTHERN COLORADO/NORTHERN NEW MEXICO ROCKIES...THIS COULD
STRENGTHEN FOR A PERIOD SOUTHWARD TOWARD THE RED RIVER VALLEY.
BUT...LARGE-SCALE ASCENT ASSOCIATED WITH A WEAK FRONTAL WAVE ACROSS
PARTS OF CENTRAL/EASTERN OKLAHOMA STILL SEEMS LIKELY TO PROVIDE THE
PRIMARY FORCING/FOCUS FOR THE MOST SIGNIFICANT NEW STORM DEVELOPMENT
LATE THIS AFTERNOON AND EVENING. EARLIER OUTLOOK REASONING APPEARS
ON TRACK.
...CNTRL GULF STATES...
A CONVECTIVELY GENERATED OR ENHANCED BOUNDARY EXTENDING ACROSS PARTS
OF CENTRAL MISSISSIPPI AND ALABAMA MAY REMAIN A FOCUS FOR LOW SEVERE
PROBABILITIES INTO THE EVENING HOURS. THIS COULD INCLUDE AN
ISOLATED TORNADO OR TWO...BUT ANY SUCH ACTIVITY STILL APPEARS LIKELY
TO REMAIN RELATIVELY SHORT-LIVED AND LIMITED BY WEAK AMBIENT
LOW-LEVEL FLOW FIELDS/SHEAR PROFILES.
...NEW MEXICO...
IT STILL APPEARS THAT DESTABILIZATION/FORCING ASSOCIATED WITH THE
DIGGING SHORT WAVE IMPULSE...EMBEDDED WITHIN A DEVELOPING
LARGER-SCALE CIRCULATION...WILL BE SUFFICIENT FOR ONE OR TWO
STRONG/MARGINALLY SEVERE STORMS LATE THIS AFTERNOON AND EVENING.
THE STRENGTHENING LOW-LEVEL BAROCLINIC ZONE ON THE EDGE OF STRONGER
SURFACE HEATING APPEARS TO BE CONFINED A BIT CLOSER TO THE HIGHER
TERRAIN...AND THE 5% SEVERE PROBABILITIES HAVE BEEN ADJUSTED
ACCORDINGLY.
..KERR/COOK.. 09/21/2009
.PREV DISCUSSION... /ISSUED 1128 AM CDT MON SEP 21 2009/
...SYNOPSIS...
A MID-UPPER SPEED MAX OVER WRN WY/ERN UT/WRN CO THIS MORNING WILL
DIG SSEWD WHILE THE BROADER SYNOPTIC SYSTEM EVOLVES INTO A CLOSED
MID LEVEL LOW OVER THE HIGH PLAINS THROUGH TONIGHT. AN ASSOCIATED
SURFACE COLD FRONT WILL CONTINUE TO MOVE EWD ACROSS ERN KS/IA/WRN
MO...AND SEWD ACROSS OK AND NW TX THROUGH EARLY TUESDAY. THIS FRONT
WILL SERVE AS THE PRIMARY FOCUS FOR THUNDERSTORM DEVELOPMENT THROUGH
THE PERIOD.
...SRN PLAINS THIS AFTERNOON/EVENING...
BOUNDARY LAYER DEWPOINTS OF 65-70 F HAVE RETURNED NWD IN ADVANCE OF
THE COLD FRONT ACROSS TX/OK/SE KS...BENEATH A PLUME OF 7 C/KM MID
LEVEL LAPSE RATES. THE COMBINATION OF ASCENT ALONG THE FRONT AND
DAYTIME HEATING WILL REMOVE THE CONVECTIVE INHIBITION NOTED IN
REGIONAL 12Z SOUNDINGS AND SUPPORT SURFACE-BASED THUNDERSTORM
DEVELOPMENT ALONG THE FRONT AROUND EARLY-MID AFTERNOON
ACROSS KS/OK. CONVECTION IS THEN EXPECTED TO DEVELOP SWD ALONG THE
FRONT TO NEAR THE RESIDUAL LEE CYCLONE TRIPLE POINT IN NW TX...AND
THEN SPREAD SEWD ACROSS CENTRAL/ERN OK AND N/NE TX THIS EVENING INTO
EARLY TONIGHT. THE MORNING ELEVATED THUNDERSTORMS AND CLOUDS OVER
ERN KS WILL TEND TO LIMIT DESTABIZATION TO THE N OF OK THIS
AFTERNOON.
THE EVOLUTION OF THE SYNOPTIC SYSTEM SUGGESTS THAT THE STRONGEST
LOW-MID LEVEL ASCENT AND DEEP LAYER VERTICAL SHEAR WILL BE CONFINED
TO AREAS ALONG AND W OF THE SURFACE COLD FRONT. THIS...COMBINED
WITH DEEP LAYER FLOW/SHEAR LARGELY PARALLEL TO THE FRONT...AND
FRONTAL MOTION TO THE E/SE THAT IS THE SAME OR FASTER THAN CELL
MOTIONS...SUGGESTS THAT CONVECTION WILL LIKELY EVOLVE INTO AN
EXTENSIVE FRONTAL SQUALL LINE BY THIS EVENING. LARGE HAIL AND
DAMAGING WINDS WILL BE THE MAIN CONCERNS AS A RESULT OF RATHER
MODEST WARM SECTOR VERTICAL SHEAR AND AFTERNOON MLCAPE VALUES OF
2000-3000 J/KG.
...NE NM AND VICINITY THIS AFTERNOON...
STRONG MID LEVEL ASCENT IMMEDIATELY DOWNSTREAM FROM THE DIGGING MID
LEVEL TROUGH WILL COINCIDE WITH POST-FRONTAL UPSLOPE FLOW THIS
AFTERNOON ACROSS NE NM. THE INITIAL REFLECTION OF THIS REGIME IS
THE ONGOING CONVECTION THAT IS SPREADING SWD TOWARD S CENTRAL CO
ATTM...AND THIS BAND OF THUNDERSTORMS SHOULD CONTINUE TO DEVELOP SWD
INTO NM THIS AFTERNOON. THOUGH INSTABILITY WILL BE RELATIVELY
WEAK... STEEPENING LOW-MID LEVEL LAPSE RATES AND STRONG DEEP LAYER
VERTICAL SHEAR SHOULD SUPPORT A FEW ORGANIZED CELLS AND/OR LINE
SEGMENTS CAPABLE OF PRODUCING MARGINALLY SEVERE HAIL AND STRONG
OUTFLOW WINDS.
...CENTRAL/NE MS AND CENTRAL AL THIS AFTERNOON...
THUNDERSTORMS WILL CONTINUE TO BE FOCUSED ALONG A DIFFUSE WARM FRONT
WHICH IS BEING REINFORCED BY ONGOING CLOUDS/RAINFALL N OF THE
BOUNDARY. RICH TROPICAL MOISTURE IS FEEDING INTO THIS WEAK
BAROCLINIC ZONE FROM THE S/SW...AND THE COMBINATION OF THIS MOISTURE
AND A DEEP LAYER OF CONDITIONALLY UNSTABLE LAPSE RATES SUPPORTS
MLCAPE VALUES NEAR 2000 J/KG. LOW-LEVEL AND DEEP LAYER VERTICAL
SHEAR ARE SLIGHTLY ENHANCED ALONG THE WEAK FRONT...WHERE PERSISTENT
MULTICELLS AND MARGINAL SUPERCELLS WILL BE POSSIBLE THROUGH THE
AFTERNOON. ISOLATED/MARGINALLY SEVERE HAIL AND STRONG WIND GUSTS
WILL BE POSSIBLE WITH THE STRONGER STORMS.
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