Mesoscale Discussion 39

Issued

Jan 21, 2012, 4:20 AM CST (10:20 UTC)

Expired

Jan 21, 2012, 5:15 AM CST

In force

55 min

Issued by

the Storm Prediction Center

The Birmingham radar (KBMX), 54 km from the middle of the area, began a volume at 10:22 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Tornado Watch 3Jan 21, 4:55 AM CST

664 
ACUS11 KWNS 211020
SWOMCD
SPC MCD 211020 
GAZ000-NCZ000-TNZ000-ALZ000-MSZ000-211115-

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

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

ATTN...WFO...MRX...FFC...OHX...BMX...HUN...MEG...JAN...

LAT...LON   33878986 34858775 35838561 35668443 34648381 33978319
            33598301 32758448 32378591 32288686 32498836 32648919
            32878979 33229000 33878986

Mesoscale Discussions in Georgia, 2012Mesoscale Discussions in Alabama, 2012Mesoscale Discussions in Mississippi, 2012Every mesoscale discussion in 2012

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; radar from the NEXRAD Level II archive.