SWODY1
SPC AC 022000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT THU APR 02 2009
VALID 022000Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE
SOUTHEAST U.S....
...MID MS/TN/OH VALLEYS...
STORMS ARE INCREASING ATTM OVER SRN AND CENTRAL AR INVOF THE UPPER
LOW...AND WHILE THE AIRMASS AHEAD OF THIS FEATURE HAS BEEN
STABILIZED SOMEWHAT BY EARLIER CONVECTION...STORMS SHOULD CONTINUE
TO INCREASE IN BOTH COVERAGE/INTENSITY WITH TIME.
SOME AIRMASS RECOVERY IS EXPECTED INVOF THE MS RIVER AND INTO ERN AR
IN THE WAKE OF THE EARLIER CONVECTION...AND WITH FAVORABLY-SHEARED
ENVIRONMENT...SEVERE THREAT SHOULD INCREASE OVER THE NEXT FEW HOURS
AHEAD OF THE COLD FRONT. WITH TIME...EXPECT THIS THREAT -- WHICH
INCLUDES THE POTENTIAL FOR ISOLATED TORNADOES -- TO SPREAD ENEWD
INTO NRN MS AND WRN TN...AND LATER ACROSS WRN KY IN THE WAKE OF
ONGOING SEVERE STORMS NOW OCCURRING OVER THIS AREA.
...AL/TN/KY/GA/N FL...
WHILE THE INITIAL CLUSTER OF STORMS CROSSING THE NRN FL PENINSULA
HAS WEAKENED...INTENSIFICATION OF STORMS IS OCCURRING ALONG THE GULF
COAST FROM FAR SERN MS EWD INTO THE FL PANHANDLE. WHILE THE STORMS
NOW APPROACHING MOBILE AL ARE LIKELY SURFACE BASED...CONVECTION
FARTHER E APPEARS TO BE SLIGHTLY ELEVATED ATOP A PRIOR OUTFLOW
BOUNDARY WHICH HAS PUSHED SWD INTO THE NERN GULF. WITH CONVECTION
OVER N FL WEAKENING...THIS BOUNDARY MAY WEAKEN WITH TIME --
SUPPORTING A INCREASING THREAT FOR DAMAGING WINDS AND ISOLATED
TORNADOES.
FARTHER NORTH INTO FAR ERN MS AND MUCH OF AL AND THE ERN 2/3 OF
TN...STORMS CONTINUE -- PRIMARILY IN A N-S BAND NEAR THE MS/AL
BORDER. WITH AOB 1000 J/KG MIXED-LAYER CAPE AND FAVORABLY-STRONG
SHEAR OVER THIS REGION...SEVERE THREAT CONTINUES. WITH MUCH OF THE
CONVECTION QUASI-LINEAR...MAIN SEVERE THREAT APPEARS TO BE DAMAGING
WINDS. ISOLATED TORNADOES REMAIN POSSIBLE...BUT THE THREAT FOR
MULTIPLE LONG-LIVED/DAMAGING TORNADOES HAS DECREASED JUST SLIGHTLY
ACROSS THIS REGION.
EVENTUALLY...CONVECTION WILL SPREAD INTO ERN TN AND ACROSS WRN GA --
ALONG WITH ASSOCIATED SEVERE THREAT. HOWEVER...WITH THE LOSS OF
DAYTIME HEATING -- AND THE SLOW-TO-OCCUR EROSION OF THE COOLER/MORE
STABLE DAMMING AIRMASS OVER NRN GA -- THE SEVERE THREAT SHOULD
DECREASE SLOWLY WITH TIME OVERNIGHT ACROSS THIS AREA. IN
ADDITION...THE THREAT WILL END OVERNIGHT FROM W-E OVERNIGHT ACROSS
THE REGION WITH THE PASSAGE OF THE MAIN SURFACE COLD FRONT.
...ERN CAROLINAS...
SOME DESTABILIZATION IS FORECAST LATE IN THE PERIOD AS A SURFACE LOW
DEEPENS W OF THE APPALACHIANS. WITH STRONG FLOW OVERSPREADING THIS
AREA AHEAD OF THE APPROACHING COLD FRONT...AREAS WHERE SURFACE-BASED
DESTABILIZATION CAN OCCUR -- POTENTIALLY OVER ERN PORTIONS OF THE
CAROLINAS -- WOULD BE SUBJECT TO AN INCREASING THREAT FOR
LOCALLY-DAMAGING WINDS AND AN ISOLATED TORNADO.
..GOSS.. 04/02/2009
.PREV DISCUSSION... /ISSUED 1139 AM CDT THU APR 02 2009/
...SYNOPSIS...
COMPLICATED SCENARIO TODAY WITH THE LARGE ONGOING MCS ACROSS THE NE
GULF COAST...AND PRE-FRONTAL CONVECTION SURGING EWD FROM LA/AR
TOWARD MS AS OF MID-LATE MORNING. THESE CONVECTIVE SYSTEMS WILL
HAVE A POTENTIALLY LARGE IMPACT ON THE SEVERE WEATHER THREAT TODAY
INTO AT LEAST EARLY TONIGHT.
...MCS FROM NE GULF COAST TO S GA THROUGH EARLY TONIGHT...
THE TRAINING CONVECTION WITHIN THE GULF COAST MCS WILL LIKELY
PERSIST THROUGH THE AFTERNOON WHILE SPREADING ENEWD ACROSS N FL/S
GA/SRN SC. THIS CONVECTION WILL BE SUSTAINED BY A CONTINUED INFLUX
OF 68-70 F BOUNDARY LAYER DEWPOINTS FROM THE NE GULF OF MEXICO...AND
IN THE ZONE OF LOW-LEVEL WAA AND UPPER DIVERGENCE ASSOCIATED WITH A
SPEED MAX EMBEDDED WITHIN THE SUBTROPICAL JET. A GRADUAL INCREASE
IN THE MAGNITUDE OF THE LLJ AND RESULTANT LOW-LEVEL SHEAR WILL
RESULT IN AN INCREASE IN THE THREAT FOR EMBEDDED SUPERCELLS WITH
TORNADOES IN THE LARGER CONVECTIVE SYSTEM THIS AFTERNOON INTO EARLY
TONIGHT.
...PRE-FRONTAL CONVECTION TODAY ACROSS LA/MS/AL/TN...
THE PRE-FRONTAL CONVECTION CROSSING THE MS RIVER /WITH AN
ACCOMPANYING COLD POOL AND POSSIBLE GRAVITY WAVE/ WILL LIKELY SWEEP
EWD ACROSS MUCH OF MS BY EARLY AFTERNOON AND INTO AL. 15Z SOUNDINGS
FROM JAN/LIX HAVE SHOWN SOME LOW-LEVEL DRYING SINCE 12Z...BUT STEEP
MID LEVEL LAPSE RATES WILL STILL SUPPORT MODERATE-STRONG INSTABILITY
/MLCAPE OF 1500-2000 J/KG/ WITH DAYTIME HEATING. VERTICAL SHEAR
WILL BE SUFFICIENT FOR SUPERCELLS WITHIN THE PRE-FRONTAL CONVECTIVE
BAND...WHILE LOW-LEVEL SHEAR/MOISTURE APPEAR TO BE LARGE ENOUGH TO
SUPPORT A FEW TORNADOES. FARTHER E...THE DISTRIBUTION OF LOW-LEVEL
MOISTURE/SURFACE HEATING AND RESULTANT INSTABILITY IS IN QUESTION
ACROSS AL GIVEN THE RELATIVELY EARLY ARRIVAL OF THE PRE-FRONTAL
LINE...AND THE ONGOING CONVECTION WITH RAIN-COOLED AIR ACROSS SE AL.
STILL...THE PRESENCE OF BOUNDARY LAYER DEWPOINTS IN THE 60S AND AT
LEAST WEAK INSTABILITY WILL SUPPORT SOME THREAT FOR SUPERCELLS/BOW
ECHOES WITH THE PRE-FRONTAL CONVECTION THIS AFTERNOON.
...SYNOPTIC LOW ACROSS AR/TN/NRN MS AND AL LATE EVENING...
THE PRE-FRONTAL CONVECTION WILL REDUCE INSTABILITY THROUGH THE
MAJORITY OF THE INLAND WARM SECTOR ACROSS THE LOWER MS VALLEY BY
MID-LATE AFTERNOON. THIS WILL LEAVE A NARROW BELT OF SURFACE
HEATING AND RESIDUAL MOISTURE ACROSS THE ARKLAMISS REGION LATER THIS
AFTERNOON...ALONG THE SYNOPTIC COLD FRONT AND NEAR THE CYCLONE
CENTER /WHICH IS NOW JUST W OF TXK/. THIS REGION OF STRONG FORCING
WILL THEN SPREAD EWD OVER NRN MS/TN/NRN AL THROUGH THE EVENING/EARLY
TONIGHT. THE MOST FAVORABLE WIND PROFILES FOR TORNADIC SUPERCELLS
ARE EXPECTED IMMEDIATELY E/SE OF THE SURFACE LOW ACROSS THE MDT RISK
AREA IN MS/AL...WHERE AN ISOLATED STRONG TORNADO OR TWO COULD STILL
OCCUR LATER THIS EVENING. THE PRIMARY UNCERTAINTY ACROSS NRN MS/WRN
AND MIDDLE TN/NRN AL WILL BE THE DEGREE OF RECOVERY/ DESTABILIZATION
IN THE WAKE OF THE AFTERNOON STORMS.
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