SWODY1
SPC AC 131952
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0252 PM CDT MON JUL 13 2009
VALID 132000Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN AND CNTRL HIGH
PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE OZARKS/ERN OK SEWD
ACROSS THE LOWER MS VALLEY...
...NRN PLAINS AND ROCKIES...
PREVIOUS FORECAST REASONING APPEARS ON TRACK ACROSS THE NRN ROCKIES
AND ADJACENT AREAS OF THE NRN HIGH PLAINS. REFER TO LATEST MESOSCALE
AND WATCH DISCUSSIONS IN THESE AREAS FOR ADDITIONAL DETAILS ON THE
DEVELOPING SEVERE WEATHER.
...LOWER MS VALLEY...
THE PROSPECTS FOR ADDITIONAL STORM DEVELOPMENT ALONG WEAKLY
CONVERGENT OUTFLOW BOUNDARIES FROM THE OZARKS SEWD ACROSS PARTS OF
THE DELTA APPEAR LIMITED GIVEN VERY WEAK LARGE SCALE SUPPORT AND
ABUNDANT WARM AIR ALOFT. HOWEVER...GIVEN INTENSE SURFACE HEATING
WITH TEMPERATURES EXCEEDING 100F IN PARTS OF THE AREA...IT APPEARS
THAT CONDITIONAL POTENTIAL DOES EXIST FOR SOME DAMAGING DOWNBURSTS.
HAVE ATTEMPTED TO CONFINE THE HIGHER SEVERE WIND PROBABILITIES TO
THE CORRIDOR WHERE GREATEST DESTABILIZATION AND WEAK LOW LEVEL
CONVERGENCE CURRENTLY COEXIST.
..CARBIN.. 07/13/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT MON JUL 13 2009/
...NRN AND CENTRAL HIGH PLAINS THIS AFTERNOON/TONIGHT...
A STRONG MID LEVEL TROUGH OVER ID WILL CONTINUE EWD OVER MT/WY TO
THE NRN HIGH PLAINS BY TONIGHT. AN ASSOCIATED SURFACE CYCLONE IS
EXPECTED TO DEVELOP TODAY INVOF THE MT/WY/SD BORDER INTERSECTION AND
THEN PROGRESS EWD NEAR THE SD/ND BORDER THROUGH TONIGHT...WHILE A
SURFACE WARM FRONT LIFTS SLOWLY NWD ACROSS SD. THIS CYCLONE...ALONG
WITH A TRAILING LEE TROUGH AND THE SURFACE WARM FRONT...WILL PROVIDE
A FOCUS FOR SEVERE THUNDERSTORM DEVELOPMENT THIS AFTERNOON THROUGH
TONIGHT.
IN THE SHORT TERM...A LEAD SHORTWAVE TROUGH AND ASSOCIATED LOW-LEVEL
WAA ARE SUPPORTING THE DEVELOPMENT OF SLIGHTLY ELEVATED
THUNDERSTORMS FROM SW ND INTO N/NW SD. SOME OF THESE STORMS WILL
MAINTAIN SUPERCELL STRUCTURES AND BE CAPABLE OF PRODUCING LARGE HAIL
THROUGH THE AFTERNOON. MEANWHILE...BOUNDARY LAYER DEWPOINTS IN THE
LOW-MID 60S ARE RETURNING NWWD ACROSS NEB AND SRN/WRN SD TOWARD SE
MT...AND THIS TREND SHOULD CONTINUE IN RESPONSE TO THE DEVELOPMENT
OF A SLY LLJ DOWNSTREAM FROM THE EJECTING NRN ROCKIES TROUGH. THIS
MOISTURE AND SURFACE HEATING IN THE RELATIVELY NARROW WARM
SECTOR...BENEATH STEEP MID LEVEL LAPSE RATES...WILL RESULT IN MLCAPE
VALUES NEAR 2000 J/KG THIS AFTERNOON FROM WRN NEB INTO WRN SD.
SURFACE-BASED THUNDERSTORMS ARE EXPECTED TO DEVELOP NEAR THE SURFACE
CYCLONE AND ALONG THE TRAILING LEE TROUGH FROM SE MT INTO EXTREME
E/NE WY BY MID-LATE AFTERNOON...AND THEN CONVECTION WILL SPREAD EWD
INTO WRN NEB/SD AND ND THROUGH LATE EVENING. INSTABILITY AND
VERTICAL SHEAR PROFILES WILL FAVOR SUPERCELLS WITH THE POTENTIAL FOR
VERY LARGE HAIL AND DAMAGING WINDS...WHILE LOW-LEVEL MOISTURE AND
INCREASING LOW-LEVEL SHEAR NEAR THE WARM FRONT WILL BE SUPPORTIVE OF
A FEW TORNADOES LATER THIS AFTERNOON/EVENING.
FARTHER S INTO CO...BOUNDARY LAYER DEWPOINTS SHOULD HOLD IN THE
55-60 F RANGE AWAY FROM THE LOCAL DOWNSLOPE INFLUENCE OF A WEAK
DENVER CYCLONE. A BELT OF MID LEVEL MOISTURE...ASSOCIATED WITH A
WEAK SPEED MAX EJECTING NEWD FROM THE GREAT BASIN...WILL CONTRIBUTE
TO STORM FORMATION THIS AFTERNOON ALONG THE FRONT RANGE. DEEP LAYER
SHEAR WILL BE MARGINALLY FAVORABLE FOR ORGANIZED
STORMS/CLUSTERS...WITH LARGE HAIL AND DAMAGING WINDS THE MAIN
THREATS THIS AFTERNOON INTO EARLY TONIGHT AS STORMS SPREAD EWD ONTO
THE PLAINS.
...LOWER MS VALLEY TO THE NRN OK/SRN KS AREA THIS AFTERNOON...
SEVERAL CLUSTERS OF STORMS ARE MOVING SWD/SEWD ACROSS CENTRAL AL/MS
AND ERN AR/NW MS...NEAR AND S OF A STALLED FRONT AND BELT OF NWLY
FLOW AROUND THE PERIPHERY OF THE SRN PLAINS MID LEVEL HIGH. STRONG
SURFACE HEATING TO THE S/SW OF THE ONGOING STORMS FROM SRN AR INTO
LA/MS/SW AL AND AN INFLUX OF LOW 70S BOUNDARY LAYER DEWPOINTS WILL
CONTRIBUTE TO MLCAPE VALUES AOA 2000 J/KG...AND THE POTENTIAL FOR
ADDITIONAL THUNDERSTORM DEVELOPMENT THIS AFTERNOON ALONG THE
COMPOSITE OUTFLOW BOUNDARY. GIVEN 20-30 KT LOW-MID LEVEL FLOW AND
EFFECTIVE BULK SHEAR APPROACHING 30 KT...A FEW ORGANIZED MULTICELL
CLUSTERS WITH DAMAGING OUTFLOW GUSTS WILL BE POSSIBLE.
THUNDERSTORM DEVELOPMENT IS LESS CERTAIN FARTHER NW INTO NRN OK AND
SRN KS ALONG THE OUTFLOW REINFORCED FRONTAL ZONE...WHERE THE CAP IS
STRONGER IN PROXIMITY TO THE MID LEVEL HIGH OVER THE SRN HIGH
PLAINS. STILL...IF STORMS DEVELOP ALONG THE BOUNDARY AS HOT SURFACE
TEMPERATURES ERODE CONVECTIVE INHIBITION...THERE WILL BE SOME THREAT
FOR DAMAGING OUTFLOW WINDS AND ISOLATED LARGE HAIL.
...MAINE AREA THIS AFTERNOON...
AN EMBEDDED SHORTWAVE TROUGH IS ROTATING EWD OVER NRN NEW
ENGLAND/SRN QUEBEC TOWARD MAINE THIS AFTERNOON. DESPITE RATHER COOL
SURFACE TEMPERATURES AND SURFACE DEWPOINTS ONLY IN THE MID 40S TO
LOW 50S...COOL TEMPERATURES ALOFT WILL RESULT IN SUFFICIENT
INSTABILITY FOR STORMS WITH SMALL/MARGINALLY SEVERE HAIL THIS
AFTERNOON.
...ERN NC THIS AFTERNOON...
WIDESPREAD CLOUDS/RAIN ARE ALREADY OVERSPREADING ERN NC IN ADVANCE
OF A REMNANT MCV FROM CONVECTION YESTERDAY ACROSS THE LOWER OH AND
TN VALLEYS. THIS WILL LIMIT DAYTIME HEATING AND THE MAGNITUDE OF
INSTABILITY THIS AFTERNOON...THUS THE THREAT FOR MORE WIDESPREAD
DAMAGING WINDS APPEARS TO HAVE DIMINISHED.
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