SWODY1
SPC AC 121956
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT SUN JUL 12 2009
VALID 122000Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF VA/NC...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL HIGH PLAINS TO
THE MIDDLE MS VALLEY/MID-SOUTH...
...VA/NC THROUGH EARLY EVENING...
ALONG/SOUTH OF VA COLD FRONT...ISOLATED TO SCATTERED SEVERE TSTMS
WILL CONTINUE TO DEVELOP AND SPREAD EAST-SOUTHEASTWARD ACROSS
SOUTHEAST/EASTERN VA AND NORTHERN NC THROUGH LATE AFTERNOON/EARLY
EVENING. THE COMBINATION OF MODERATE INSTABILITY /1000-2000 J PER KG
MLCAPE PER LATEST OBJECTIVE ANALYSIS/ AND EFFECTIVE BULK SHEAR
AROUND 40 KT /IMPLIED FROM REGIONAL WSR-88D VWP DATA/ WILL SUPPORT A
FEW SUPERCELLS/ORGANIZED MULTICELLULAR CLUSTERS CAPABLE OF MAINLY
DAMAGING WINDS/PERHAPS A BRIEF TORNADO.
...MIDDLE MS/TN VALLEYS AND MID-SOUTH...
STRONG/OCCASIONALLY SEVERE QUASI-LINEAR MCS CONTINUES TO PROGRESS
EASTWARD ACROSS FAR SOUTHERN IL AND THE ADJACENT LOWER OH RIVER
VALLEY AT MID AFTERNOON. WHILE MODERATELY STRONG WIND FIELDS ARE
NOTED IN THE WAKE/ON THE PERIPHERY OF THIS MCS /REFERENCE CONWAY MO
PROFILER/...BROADER/DOWNSTREAM ENVIRONMENT DOES NOT APPEAR
PARTICULARLY FAVORABLE FOR APPRECIABLE MCS-INTENSIFICATION.
NEVERTHELESS...MAINLY DAMAGING WINDS WILL CONTINUE TO BE POSSIBLE
THROUGH AROUND SUNSET...BOTH WITH THE LOOSE PERSISTENCE OF THE MCS
AND ANY LEADING/PERIPHERAL PULSE-TYPE TSTMS ACROSS THE TN VALLEY
WITHIN A MODERATE TO STRONGLY UNSTABLE AIRMASS.
LATER TONIGHT...AS A WESTERLY LOW LEVEL JET IMPINGES UPON THE
SYNOPTIC SURFACE FRONTAL ZONE/RESIDUAL OUTFLOW...IT SEEMS PROBABLE
THAT ADDITIONAL BOUTS OF SCATTERED ELEVATED TSTMS /SOME SEVERE/ WILL
DEVELOP ACROSS THE OZARKS/MID-SOUTH VICINITY.
...ELSEWHERE...
WITH FEW OTHER CHANGES TO PRIOR CONVECTIVE OUTLOOK...CONSULT
DISCUSSION BELOW FOR CENTRAL HIGH PLAINS/NORTHERN ROCKIES SEVERE
THREATS LATER THIS AFTERNOON/EVENING. ALSO REFERENCE MESOSCALE
DISCUSSION 1536 REGARDING THE HIGH PLAINS.
..GUYER.. 07/12/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT SUN JUL 12 2009/
...MO/MS VALLEY REGION TODAY INTO TONIGHT...
A COUPLE OF THUNDERSTORM CLUSTERS ARE ONGOING OVER CENTRAL MO AND
WRN IA AS OF LATE MORNING...WHILE OVERNIGHT CONVECTION HAS LARGELY
DISSIPATED FARTHER S ACROSS NW MS/ERN AR. THE WRN IA STORMS APPEAR
TO BE ASSOCIATED WITH LOW-LEVEL WAA AND ASCENT IN THE RIGHT ENTRANCE
REGION OF AN UPPER JET STREAK ROTATING AROUND THE SWRN PERIPHERY OF
THE CLOSED LOW OVER JAMES BAY. THIS CLUSTER WILL PERSIST WITH AT
LEAST A MARGINAL HAIL/WIND THREAT FOR THE NEXT FEW HOURS...THOUGH
LONGER TERM TRENDS ARE UNCERTAIN GIVEN THE RECENT CONVECTIVE
OVERTURNING JUST DOWNSTREAM FROM THESE STORMS...ACROSS NE KS/NW MO.
MEANWHILE...THE CENTRAL MO CLUSTER HAS BEEN DEVELOPING INTO THE ZONE
OF ENHANCED STORM-RELATIVE INFLOW ALONG THE SYNOPTIC FRONT...AND
SOME PORTION OF THIS MCS COULD PERSIST INTO THE AFTERNOON WITH THE
THREAT FOR DAMAGING WINDS/HAIL WHILE MOVING TOWARD THE CONFLUENCE OF
THE MS/OH RIVERS.
ADDITIONAL THUNDERSTORM DEVELOPMENT COULD OCCUR THIS AFTERNOON ALONG
THE OUTFLOW BOUNDARY TRAILING FROM THE CENTRAL MO STORMS...FROM SE
KS INTO SW MO...AND FARTHER S INTO AR/MS ALONG THE FRINGES OF THE
THICKER CLOUDS AND ALONG ANY DIFFUSE/LINGERING OUTFLOW BOUNDARIES
FROM THE OVERNIGHT STORMS. LATER TONIGHT...THE WSWLY LLJ WILL AGAIN
DEVELOP OVER OK AND MAY FOCUS ELEVATED THUNDERSTORM FORMATION AFTER
06Z ON THE COOL SIDE OF THE SYNOPTIC FRONT/COMPOSITE OUTFLOW...FROM
SE KS INTO SW MO AND NRN AR.
...CENTRAL HIGH PLAINS THIS AFTERNOON/EVENING...
THE MID LEVEL RIDGE AXIS RESIDES OVER THE HIGH PLAINS...THOUGH
EMBEDDED SPEED MAXIMA CONTINUE TO MOVE NEWD THEN EWD FROM UT TO
WY/NRN CO. BOUNDARY LAYER DEWPOINTS REMAIN IN THE 55-60 F RANGE
ACROSS ERN CO AND ERN WY...AND WEAK LOW-LEVEL UPSLOPE FLOW IS
EXPECTED THIS AFTERNOON. ONCE SURFACE TEMPERATURES WARM INTO THE
MID-UPPER 80S...THUNDERSTORM DEVELOPMENT IS EXPECTED FROM THE CO
FRONT RANGE AND FOOTHILLS NWD TO JUST E OF THE LARAMIE RANGE AND
NEAR THE BLACK HILLS. MLCAPE OF 1000-1500 J/KG AND EFFECTIVE BULK
SHEAR AOA 40 KTS WILL SUPPORT SUPERCELLS CAPABLE OF PRODUCING LARGE
HAIL AND DAMAGING GUSTS THROUGH THE LATE AFTERNOON/EVENING. STORM
MERGERS/INTERACTIONS AND A WEAK SLY LLJ COULD ALLOW ONE OR MORE
CLUSTERS TO PERSIST OVERNIGHT WHILE SPREADING EWD ACROSS NE CO/NW
KS/WRN NEB.
...VA/NC AREA THIS AFTERNOON...
12Z SOUNDINGS REVEALED MOIST LOW-LEVEL PROFILES AND RATHER POOR MID
LEVEL LAPSE RATES. HOWEVER...SUBSTANTIAL SURFACE HEATING IS
UNDERWAY ACROSS VA/NC...AND MLCAPE AROUND 1000 J/KG IS EXPECTED THIS
AFTERNOON. ADDITIONALLY...A SURFACE COLD FRONT IS DRIFTING SWD
ACROSS CENTRAL VA...ALONG THE SRN PERIPHERY OF THE STRONGER MID
LEVEL FLOW AROUND THE JAMES BAY CLOSED LOW. THE COMBINATION OF
POTENTIALLY MODERATE INSTABILITY AND EFFECTIVE BULK SHEAR NEAR 40 KT
/ESPECIALLY OVER VA/ SHOULD BE SUFFICIENT FOR A FEW ORGANIZED
MULTICELL CLUSTERS AND/OR SUPERCELLS CAPABLE OF PRODUCING A FEW
DAMAGING GUSTS THIS AFTERNOON.
...NRN ROCKIES AREA THIS AFTERNOON INTO EARLY TONIGHT...
A PRONOUNCED MID LEVEL TROUGH IS MOVING SLOWLY EWD OVER
WA/ORE...TOWARD ID/WRN MT BY THE END OF THE PERIOD. ONLY MODEST
LOW-MID LEVEL MOISTURE RESIDES DOWNSTREAM FROM THIS TROUGH FROM THE
NRN GREAT BASIN INTO THE NRN ROCKIES...AND IT APPEARS THAT
INSTABILITY WILL BE SOMEWHAT LIMITED THROUGH THE PERIOD.
HOWEVER...GIVEN STEEP LOW-MID LEVEL LAPSE RATES AND A GRADUAL
INCREASE IN LOW-MID LEVEL FLOW WITH THE APPROACH OF THE TROUGH...A
FEW STORMS COULD PRODUCE STRONG OUTFLOW WINDS AND PERHAPS MARGINALLY
SEVERE HAIL. THE MORE PROBABLE AREAS FOR SUCH ACTIVITY LATER THIS
AFTERNOON/EVENING WILL BE FROM CENTRAL/NE ORE INTO ERN WA
IMMEDIATELY IN ADVANCE OF THE TROUGH...AND OVER THE HIGHER TERRAIN
OF SW MT.
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