Alert archive / Georgia / Mesoscale Discussions in 2012

Mesoscale Discussion 2221

December 25, 20126 counties in Florida; 29 counties in Georgia

The Storm Prediction Center issued this mesoscale discussion at Dec 25, 2012, 6:57 PM EST for 6 counties in Florida; 29 counties in Georgia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Dec 25, 2012, 6:57 PM EST (23:57 UTC)
Expired: Dec 25, 2012, 9:00 PM EST
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 35 counties

Gadsden County, FL, Jefferson County, FL, Leon County, FL, Liberty County, FL, Madison County, FL, Wakulla County, FL, Baker County, GA, Brooks County, GA, Calhoun County, GA, Chattahoochee County, GA, Colquitt County, GA, Cook County, GA, Crisp County, GA, Decatur County, GA, Dooly County, GA, Dougherty County, GA, Grady County, GA, Lee County, GA, Lowndes County, GA, Macon County, GA, Marion County, GA, Miller County, GA, Mitchell County, GA, Muscogee County, GA, Randolph County, GA, Schley County, GA, Stewart County, GA, Sumter County, GA, Taylor County, GA, Terrell County, GA, Thomas County, GA, Tift County, GA, Turner County, GA, Webster County, GA, Worth County, GA

The radar

The Tallahassee radar (KTLH), 99 km from the middle of the area, began a volume at 23:57 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.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Tornado Watch 698Dec 25, 10:25 PM EST

The nearest sounding before it

Tallahassee Rgnl, FL (KTLH), launched 12:00Z, 12.0 hours before the alert went out and 99 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 212 J/kg
Mixed-layer CIN: -11 J/kg
Mixed-layer LCL: 448 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 60 m²/s²
0-3 km storm-relative helicity: 64 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

084 
ACUS11 KWNS 252357
SWOMCD
SPC MCD 252357 
GAZ000-FLZ000-ALZ000-260200-

MESOSCALE DISCUSSION 2221
NWS STORM PREDICTION CENTER NORMAN OK
0557 PM CST TUE DEC 25 2012

AREAS AFFECTED...SWRN GA / ERN FL PANHANDLE

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

VALID 252357Z - 260200Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...A TORNADO WATCH WILL NEED TO BE CONSIDERED BY 01-03Z FOR
SWRN GA AND THE ERN FL PANHANDLE FOR AN INCREASING TORNADO THREAT
FROM LATE EVENING INTO THE OVERNIGHT HOURS.

DISCUSSION...LATEST SURFACE MESOANALYSIS SHOWS A DEEPENING LOW OVER
W-CNTRL MS AND AN ATTENDANT WARM FRONT EXTENDING ESEWD ACROSS THE
SRN 1/3RD OF AL INTO SWRN GA.  SURFACE TEMPS ARE IN THE LOWER-MID
60S S OF THE BOUNDARY AND DEWPOINTS RANGE FROM THE UPPER 50S TO
LOWER 60S.  2330Z TLH VWP SHOWS 150-200 M2/S2 0-1 SRH...WHEN
INPUTTING OBSERVED RIGHT-MOVING SUPERCELL STORM MOTIONS OVER SRN AL.
 
AS AN INTENSIFYING MID-LEVEL TROUGH/LOW ASSUMES AN INCREASINGLY
NEGATIVE TILT...STRONG LOW LEVEL MASS RESPONSE --LLJ FEATURING 45-55
KT 925MB SLY FLOW-- WILL CONTINUE TO SPREAD EWD OVER THE DISCUSSION
AREA TONIGHT.  VERY STRONG LOW LEVEL SHEAR --INCREASING TO 300-500
MS/S2 0-1 KM SRH-- WILL SUPPORT UPDRAFT ROTATION WITH THE MORE
VIGOROUS/SUSTAINED UPDRAFTS.  DESPITE VERY FAVORABLE
KINEMATICS...BUOYANCY WILL BECOME INCREASINGLY MARGINAL WITH FARTHER
E EXTENT TOWARDS THE I-75 CORRIDOR.  IN ADDITION TO THE RISK FOR A
TORNADIC SUPERCELL OR TWO...AN EVENTUAL LINEAR CONGLOMERATION OWING
TO STORM MERGERS/STRONG FORCING FOR ASCENT WILL FAVOR THE
DEVELOPMENT OF A QLCS MOVING EWD ACROSS THE AREA LATE
TONIGHT...POSING PRIMARILY A WIND DAMAGE THREAT.

..SMITH/HART.. 12/25/2012

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

ATTN...WFO...FFC...TAE...BMX...

LAT...LON   30838478 32678502 32718441 32368373 31118316 30008342
            29828500 30838478

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 25, 3:32 PM EST	Mesoscale Discussion	SPC	Bay, Calhoun, Escambia, Franklin, Gulf, Holmes and 6 more	28 min
Dec 25, 3:41 PM EST	Tornado Watch	SPC	Bay, Calhoun, Escambia, Gulf, Holmes, Jackson and 4 more	7 hr
Dec 25, 6:17 PM EST	Mesoscale Discussion	SPC	Escambia, Holmes, Okaloosa, Santa Rosa, Walton, Washington	88 min

Nearby

Mesoscale Discussions in Georgia, 2012 Mesoscale Discussions in Florida, 2012 Every mesoscale discussion in 2012

Sources

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.