SWODY1
SPC AC 302111
DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0411 PM CDT THU JUL 30 2009
VALID 302105Z - 311200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF CNTRL/ERN NM INTO
SWRN/SRN TX...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF TN INTO NRN/CNTRL
MS/AL...
AMENDED TO SHIFT SLIGHT RISK NWD THROUGH TN
...MID SOUTH...
A DISTINCT SUPERCELL/TORNADO THREAT HAS DEVELOPED THIS AFTERNOON
ALONG THE MS RIVER W OF MEM IN ADVANCE OF MIDLEVEL VORTICITY MAXIMUM
AND ATTENDANT SURFACE LOW ACCELERATING NEWD. THE COMBINATION OF A
MOIST/UNSTABLE AIR MASS AND STRENGTHENING VERTICAL SHEAR /REF. MEM
VWP/ IS RESULTING IN AN ENVIRONMENT FAVORABLE FOR TORNADIC
SUPERCELLS. AS MENTIONED IN 20Z OUTLOOK...THIS THREAT SHOULD
CONTINUE EWD TONIGHT ACROSS NRN PARTS OF MS/AL...AS WELL AS
WRN/MIDDLE TN.
...GULF STATES AND TN VALLEY...
CATEGORICAL SLIGHT RISK AND HIGHER WIND PROBABILITIES HAVE BEEN
ADJUSTED NWD FROM THE IMMEDIATE GULF COAST.
WELL-DEFINED VORTICITY MAXIMUM NEAR THE ARKLATEX WILL BEGIN TO
ACCELERATE NEWD THROUGH THE LOWER MS INTO TN VALLEY LATER TODAY INTO
TONIGHT IN RESPONSE TO APPROACH OF NEXT UPSTREAM SYSTEM THROUGH THE
HIGH PLAINS. AS THIS OCCURS...ATTENDANT SURFACE LOW /ANALYZED NEAR
HOT AS OF 19Z/ WILL DEVELOP NEWD THROUGH WRN/MIDDLE TN INTO ERN KY
BY FRI MORNING. TRAILING COLD FRONT WILL PUSH EWD/SEWD THROUGH THE
LOWER MS VALLEY.
WIDESPREAD CLOUDS HAVE LIMITED DAYTIME HEATING AND RESULTANT AIR
MASS DESTABILIZATION SO FAR TODAY WITHIN ZONE OF DEEPEST/STRONGEST
ASCENT OVER AR. HOWEVER...DOWNSTREAM AIR MASS OVER MS/AL INTO TN IS
EXPERIENCING STRONGER DIABATIC HEATING WHERE TEMPERATURES HAVE
WARMED THROUGH THE 80S. WHEN COUPLED WITH A MOIST BOUNDARY LAYER
/DEWPOINTS IN THE 70S/...ENVIRONMENT HAS BECOME MODERATELY UNSTABLE
WITH MLCAPE RANGING FROM 1000 J/KG OVER SRN TN...TO 2000-2500 J/KG
OVER CNTRL PARTS OF MS/AL.
LATEST NAM/GFS GUIDANCE INDICATES THAT ENHANCED GRADIENT FLOW
ATTENDANT TO MIDLEVEL VORTICITY MAXIMUM WILL SPREAD EWD ACROSS
SLIGHT RISK AREA TONIGHT. MOREOVER...AIR MASS WILL LIKELY REMAIN
WARM/UNSTABLE THROUGH THE NIGHTTIME HOURS GIVEN THE MOIST BOUNDARY
LAYER CONDITIONS. AS SUCH...SETUP WILL BE FAVORABLE FOR THE
DEVELOPMENT OF SUPERCELL AND/OR BOWING STRUCTURES FROM VICINITY OF
SURFACE LOW SWWD ALONG COLD FRONT. WHILE DAMAGING WIND GUSTS WILL
BE THE PRIMARY SEVERE THREATS...ISOLATED TORNADOES WILL BE POSSIBLE.
VERTICAL SHEAR WILL REMAIN MARGINAL FOR STORM ORGANIZATION S OF
I-20...THUS HIGHER SEVERE PROBABILITIES AND CATEGORICAL SLIGHT HAVE
BEEN REMOVED FROM COASTAL AREAS. NONETHELESS...SOME THREAT FOR
LOCALLY STRONG WIND GUSTS AND HAIL WILL CONTINUE INTO THIS EVENING.
...SRN HIGH PLAINS...
PREVIOUS FORECAST IS IN GOOD SHAPE WITH ONLY SMALL CHANGES MADE.
TSTMS DEVELOPING OVER THE HIGHER TERRAIN OF CNTRL NM ARE EXPECTED TO
MOVE SEWD AS AIR MASS OVER THE ADJACENT HIGH PLAINS CONTINUES TO
WARM/DESTABILIZE. THE PRESENCE OF 30-35 KT WNWLY MIDLEVEL
FLOW...ELY LOW-LEVEL WIND COMPONENT AND STEEP LAPSE RATES WILL ALL
CONTRIBUTE TO AN ENVIRONMENT FAVORABLE FOR A FEW ROTATING STORMS
CAPABLE OF HAIL AND DAMAGING WIND GUSTS.
...S TX...
MCS OVER THE EDWARDS PLATEAU SHOULD CONTINUE TO PROPAGATE GENERALLY
SWD INTO A HOT AND MOIST AIR MASS WHERE MLCAPE HAS INCREASED TO
2000-3000 J/KG. WHILE VERTICAL SHEAR REMAINS RATHER WEAK /REF. DRT
VWP/...THE PRESENCE OF THE MODERATE/STRONG INSTABILITY AND 30-35 F
T/TD SPREADS IN THE BOUNDARY LAYER SHOULD ENHANCE SYSTEM UPDRAFTS
AND COLD POOL DEVELOPMENT. SEVERE WIND GUSTS AND SOME HAIL WILL BE
POSSIBLE WITH MCS INTO THIS EVENING.
..MEAD.. 07/30/2009
.PREV DISCUSSION... /ISSUED 1139 AM CDT THU JUL 30 2009/
...SYNOPSIS...
SHORT WAVE TROUGH CENTERED OVER ERN RED RIVER VALLEY WILL TRACK EWD
INTO AR THIS AFTERNOON AND WILL BEGIN TO PHASE WITH AN UPPER MS
VALLEY TROUGH AFTER 00Z AS BOTH SYSTEMS PROGRESS DOWNSTREAM TO THE
TN VALLEY AND ACROSS THE GREAT LAKES...RESPECTIVELY. REGIONAL
RADARS AND VISIBLE SATELLITE IMAGERY INDICATE ONE OR TWO MCVS LEFT
OVER FROM THE OVERNIGHT/EARLY MORNING TX/OK MCS...AND WERE LOCATED
NEAR THE ARKLATEX AND WWD OVER SOUTH CENTRAL OK. MEANWHILE... WNWLY
MID LEVEL FLOW WILL PERSIST FROM THE FOUR CORNERS REGION TO THE SRN
PLAINS WITH THE SWRN-SRN EXTENSION OF A BROAD LONG WAVE TROUGH
LOCATED ACROSS MUCH OF THE LOWER 48 STATES.
...ERN NM INTO SW/S CNTRL TX...
GIVEN STABILIZING EFFECTS OF THE BOUNDARY LAYER IN THE WAKE OF
ONGOING CLUSTERS OF TSTMS PROGRESSING SEWD THROUGH THE EDWARDS
PLATEAU THIS MORNING...SEVERE PROBABILITIES HAVE BEEN LOWERED FROM
EAST OF MAF TO THE SWRN PORTION OF FWD COUNTY WARNING AREA. A
MODERATELY UNSTABLE AIR MASS DOWNSTREAM OF THESE ONGOING STORMS AND
EFFECTIVE BULK SHEAR EXPECTED TO STRENGTHEN THIS AFTERNOON SUGGEST
THE POTENTIAL FOR ORGANIZED STRONG TO SEVERE STORMS ACROSS SOUTH
CENTRAL TX IN THE VICINITY OF AN OUTFLOW BOUNDARY SETTLING SLOWLY
SWD.
FARTHER W...NO CHANGES HAVE BEEN MADE TO THE OUTLOOK WITH THE
LIKELIHOOD FOR DIURNALLY DRIVEN TSTMS EXPECTED ACROSS PARTS OF ERN
NM INTO SWRN TX IN THE VICINITY OF THE W/SWWD MOVING COLD FRONT AND
UPSLOPE FLOW INTO THE HIGHER TERRAIN. MODERATE INSTABILITY AND
EFFECTIVE BULK SHEAR /35-40 KT/ WILL SUPPORT SUPERCELLS WITH
DAMAGING WINDS/HAIL THE PRIMARY THREATS THIS AFTERNOON GIVEN A STEEP
LAPSE RATE ENVIRONMENT. MUCH OF THE REGION ALSO WILL LIE BENEATH
50-60 KT 250 MB JET THAT WILL ENHANCE DEEP SHEAR AND COULD ENHANCE
POTENTIAL FOR UPSCALE DEVELOPMENT OF STORMS INTO SEVERAL SMALL
FORWARD-PROPAGATING MCSS. EMBEDDED BOWING SEGMENTS WITHIN THESE
SYSTEMS COULD YIELD DMGG WIND INTO THE NIGHT OVER WRN AND SRN PARTS
OF THE OUT LOOKED AREA AS MOIST...POST FRONTAL 850 MB UPSLOPE FLOW
PERSISTS INTO THE HIGHER TERRAIN.
...E TX TO TN VLY/CNTRL GULF CST...
DESPITE THE EXISTENCE OF MODEST MID LEVEL LAPSE RATES EXTENDING
ACROSS THIS SLIGHT RISK AREA...A VERY MOIST AIR MASS /PW VALUES
AROUND 2 INCHES FROM ERN TX TO THE SRN APPALACHIANS COMBINED WITH
SURFACE HEATING WILL AID IN FURTHER DESTABILIZATION. THIS
MOISTURE/INSTABILITY COMBINED WITH FORCING FOR ASCENT ATTENDANT TO
THE RED RIVER VALLEY SHORT WAVE TROUGH/REMNANT MCVS AND A SECOND MID
LEVEL IMPULSE TRACKING EWD ACROSS AL/GA TODAY SHOULD SUPPORT SEVERAL
AREAS OF TSTM DEVELOPMENT ACROSS THIS REGION. PRONOUNCED LOWER-MID
LEVEL DRYING IN THE WAKE OF THE AL IMPULSE AS INDICATED BY 12Z UPPER
AIR ANALYSES MAY RESULT IN A MINIMUM IN TSTM ACTIVITY FOR A WHILE
THIS AFTERNOON ACROSS ERN MS/WRN AL...BUT EVENTUAL MOISTENING AHEAD
OF THE ARKLATEX MCV SUGGESTS TSTMS WILL SPREAD EWD INTO THIS REGION
AS WELL. ALTHOUGH DEEP LAYER SHEAR AND MID LEVEL LAPSE RATES WILL
BE WEAKER WITH EWD EXTENT ACROSS THE SLIGHT RISK AREA...MODERATE
INSTABILITY AND HIGH MOISTURE CONTENT/THETAE VALUES SUGGEST WET
MICROBURSTS WILL BE POSSIBLE WITH SOME HAIL THREAT. GREATER THREAT
FOR STORM ORGANIZATION SHOULD EXTEND FROM THE LOWER MS VALLEY THIS
AFTERNOON TO TN VALLEY TONIGHT AS STRONGER BAND OF SWLY MID LEVEL
WINDS/DEEP LAYER SHEAR ACCOMPANY THE SHORT WAVE TROUGH AND LLJ
INCREASES TONIGHT INTO TN VALLEY. FOR THIS REASON...THE SLIGHT RISK
AREA HAS BEEN EXPANDED NWD INTO PARTS OF SRN AR TO NRN AL/NWRN GA.
...UPR MS VLY TO LWR MI...
SCATTERED TSTMS SHOULD FORM IN WEAKLY CAPPED ENVIRONMENT AHEAD OF MN
UPPER VORT AND INVOF ASSOCIATED COLD FRONT. THIS ACTIVITY... LIKELY
TO FORM BY LATE MORNING AND CONTINUE THROUGH LATE AFTERNOON...COULD
YIELD A FEW SPOTS OF MARGINALLY SEVERE HAIL/GUSTY WINDS...WITH THE
STORMS SPREADING SEWD WITH TIME. THE SEVERE THREAT WILL BE LIMITED
BY RELATIVELY SPARSE MOISTURE AND MODEST DEEP UNIDIRECTIONAL SHEAR.
SRN PORTIONS OF THE 5% HAIL AREA WILL LIE BENEATH NRN FRINGE OF
100-110 KT 250 MB FLOW. THIS COULD POTENTIALLY AID STORM
ORGANIZATION/SUSTENANCE...BUT LOW LEVEL LAPSE RATES LIKELY WILL BE
WEAKER IN THIS REGION DUE CLOUDINESS.
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