Here is the latest thinking from our friends at the SPC. It basically says that a replacement severe weather watch will be required prior to 5 a.m. for areas southeast of the current watch.
MESOSCALE DISCUSSION 0039
NWS STORM PREDICTION CENTER NORMAN OK
0420 AM CST SAT JAN 21 2012
AREAS AFFECTED…PORTIONS SRN MIDDLE AND SERN TN…NERN/E-CENTRAL
MS…CENTRAL/NRN AL…NRN/WRN GA…EXTREME SWRN NC.
CONCERNING…TORNADO WATCH 2…
VALID 211020Z – 211115Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 2 CONTINUES.
NEW WW LIKELY WILL BE NEEDED BEFORE SCHEDULED 11Z EXPIRATION OF WW
2.
COLD-FRONTAL TSTM BAND OVER PORTIONS MIDDLE TN…NWRN AL AND NRN MS
IS BECOMING BETTER ORGANIZED..WITH POTENTIAL FOR EMBEDDED BOW/LEWP
FORMATIONS TO PRODUCE DAMAGING GUSTS. TORNADO POTENTIAL ALSO
REMAINS…BOTH WITHIN THIS ACTIVITY AND WITH ANY SUSTAINED
DEVELOPMENT OCCURRING AHEAD OF LINE. MEANWHILE…INCREASINGLY
SHALLOW LAYER OF STATIC STABILITY OVER SERN TN AND NRN GA IS
EXPECTED TO CONTINUE ERODING AMIDST CONTINUING PRE COLD-FRONTAL
WAA…WHICH WILL EFFECTIVELY SHUNT WARM FRONT NEWD ACROSS THIS AREA
WITH TIME. PRIMARY UNCERTAINTY IS IN HOW FAST THIS PROCESS OCCURS.
WARM SECTOR SHOULD REMAIN WEAKLY CAPPED FOR SFC-BASED PARCELS…WITH
MLCAPE IN 250-800 J/KG RANGE THROUGH REMAINDER PRE-DAWN
HOURS…INCREASING SLOWLY THEREAFTER.
INCREASE IN INITIALLY SHALLOW/PREFRONTAL CONVECTION OVER PORTIONS
CENTRAL/SWRN MS ALSO MAY BE EARLY MANIFESTATION OF WSW-ENE BANDS OF
TSTMS PROGGED BY A FEW CONVECTION-ALLOWING/HIGH-RES MODELS FOR LATER
THIS MORNING OVER PORTIONS ERN MS AND CENTRAL/NRN AL…AHEAD OF
COLD-FRONTAL ACTIVITY. THIS APPEARS REASONABLE…CONSIDERING
PRESENCE OF VEERING LOW-LEVEL FLOW WITH DEPARTURE OF LOW-LEVEL
CYCLONE…BUT STILL SUFFICIENT LOW-LEVEL CONVERGENCE FOR TSTMS IN
PRESENCE OF WEAK CINH. MEANWHILE…MIDLEVEL DCVA/ASCENT AND
DEEP-LAYER/EFFECTIVE SHEAR WILL OVERSPREAD MORE OF WARM SECTOR AS
SHORTWAVE TROUGH APCHS. DESPITE AFOREMENTIONED VEERING…LOW-LEVEL
SHEAR STILL SHOULD REMAIN FAVORABLE FOR BOTH BOWS AND
SUPERCELLS…WITH AREA OF EFFECTIVE SRH 300-500 J/KG SHIFTING EWD
ACROSS AL AND INTO PORTIONS WRN GA.
..EDWARDS.. 01/21/2012
