Mesoscale Discussion 2139

Issued

Sep 5, 2011, 8:36 PM EDT (00:36 UTC)

Expired

Sep 5, 2011, 10:00 PM EDT

In force

84 min

Issued by

the Storm Prediction Center

996 
ACUS11 KWNS 060037
SWOMCD
SPC MCD 060036
NCZ000-SCZ000-GAZ000-FLZ000-060200-

MESOSCALE DISCUSSION 2139
NWS STORM PREDICTION CENTER NORMAN OK
0736 PM CDT MON SEP 05 2011

AREAS AFFECTED...PORTIONS NRN FL AND ADJACENT CENTRAL/ERN FL
PANHANDLE...SRN/ERN GA...CENTRAL/ERN SC...S-CENTRAL/SERN NC.

CONCERNING...SEVERE THUNDERSTORM WATCH 841...843...

VALID 060036Z - 060200Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH
841...843...CONTINUES.

WW 841 MAY BE CLEARED FROM W-E ALONG/BEHIND EWD-MOVING SFC COLD
FRONT...WHICH WAS ANALYZED AT 00Z FROM SFC LOW OVER MIDDLE OF
AL...SSEWD THROUGH TOI AREA THEN SWD ACROSS I-10 BETWEEN CEW-MAI.
MAIN THREAT IN EACH WW REMAINS CONVECTIVE GUSTS FOR ANOTHER 2-3
HOURS...THOUGH TORNADO THREAT IS NON-ZERO.

SVR GUST THREAT SHOULD DIMINISH AFTER ABOUT 01Z AS
1. GRADUAL SFC DIABATIC COOLING IN MOIST SECTOR WILL REDUCE
INSTABILITY...INCREASE MLCINH AND DECREASE SUBCLOUD DCAPE.
2. POTENTIAL FOR SUFFICIENTLY DEEP/INTENSE CONVECTION CLEARS WW FROM
W-E...ALONG/AHEAD OF COLD FRONT AND NEARLY COLLOCATED EDGE OF
MID-UPPER LEVEL DRY SLOT...LATTER BEING QUITE EVIDENT IN MOISTURE
CHANNEL IMAGERY.

ALTHOUGH THREAT FOR SVR GUSTS WILL LESSEN WITH TIME THIS
EVENING...AT LEAST MRGL RISK MAY EXTEND SPATIALLY FARTHER E OF WW
841...AND IN GAP BETWEEN 841-843...ACROSS PORTIONS SERN GA AND NERN
FL FOR SHORT INTERVAL IN MEANTIME.

CORRIDOR OF FAVORABLE LOW-LEVEL THETAE/BUOYANCY REMAINS OVER
PREFRONTAL AREAS OF WW 841...WITH AXIS OF EACH ROUGHLY ALONG TLH-MCN
LINE AS OF 00Z.  NNEWD-MOVING BAND OF CONVECTION HAS STABILIZED AIR
MASS SLIGHTLY IN ITS WAKE...THOUGH LOW-LEVEL WAA MAY PERMIT
ADDITIONAL RECOVERY/DESTABILIZATION OVER NEXT FEW HOURS.  MODIFIED
RAOBS AND MODEL FCST SOUNDINGS SUGGESTING 500-1500 J/KG MLCAPE OVER
MOST OF GA...INCREASING SWD TO AROUND 2500 J/KG MLCAPE AS DERIVED
FROM 00Z TLH RAOB.  SUFFICIENT LOW-LEVEL SRH STILL IS PRESENT FOR AT
LEAST MRGL TORNADO THREAT...ALTHOUGH DOMINANT CONVECTIVE MODE WILL
REMAIN BANDED.  EFFECTIVE SHEAR DECREASES WITH SWD EXTENT ACROSS
THIS REGION.  THIS TREND SHOULD CONTINUE...ALONG WITH DECREASE IN
DEEP-LAYER SHEAR AT ANY GIVEN SPOT WITH TIME...AS COMBINATION OF
STRONGEST MIDLEVEL WINDS AND SFC ISALLOBARIC FORCING SHIFT NNEWD IN
STEP WITH TRANSLATION OF REMAINS OF TD LEE.

..EDWARDS.. 09/06/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MHX...RAH...ILM...CHS...CAE...GSP...TBW...JAX...
FFC...TAE...

LAT...LON   29638519 30588472 31898482 31948364 34238136 35377992
            35327796 32948032 30798205 29118305 29328322 29998388
            30058421 29788472 29638519

Mesoscale Discussions in Georgia, 2011Mesoscale Discussions in South Carolina, 2011Mesoscale Discussions in Florida, 2011Every mesoscale discussion in 2011

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive.