Alert archive / Alabama / Mesoscale Discussions in 2021

Mesoscale Discussion 2021

December 11, 202121 counties in Alabama; 7 counties in Georgia

The Storm Prediction Center issued this mesoscale discussion at Dec 11, 2021, 10:47 AM CST for 21 counties in Alabama; 7 counties in Georgia. It was in force for 118 min.

The area

The outline as issued.

The facts

Issued: Dec 11, 2021, 10:47 AM CST (16:47 UTC)
Expired: Dec 11, 2021, 12:45 PM CST
In force: 118 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

All 28 counties

Autauga County, AL, Bullock County, AL, Butler County, AL, Chambers County, AL, Clarke County, AL, Clay County, AL, Conecuh County, AL, Coosa County, AL, Crenshaw County, AL, Dallas County, AL, Elmore County, AL, Lee County, AL, Lowndes County, AL, Macon County, AL, Monroe County, AL, Montgomery County, AL, Pike County, AL, Randolph County, AL, Tallapoosa County, AL, Washington County, AL, Wilcox County, AL, Carroll County, GA, Coweta County, GA, Fayette County, GA, Harris County, GA, Heard County, GA, Meriwether County, GA, Troup County, GA

The radar

The Maxwell AFB radar (KMXX), 72 km from the middle of the area, began a volume at 16:48 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 nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 4.8 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: 245 J/kg
Mixed-layer CIN: -11 J/kg
Mixed-layer LCL: 703 m above ground
0-6 km bulk shear: 63 kt
0-1 km storm-relative helicity: 325 m²/s²
0-3 km storm-relative helicity: 371 m²/s²
Significant tornado parameter: 0.4
Supercell composite: 3.8

Open this sounding in Storm Lab

The text

As transmitted.

761 
ACUS11 KWNS 111648
SWOMCD
SPC MCD 111647 
GAZ000-ALZ000-111845-

Mesoscale Discussion 2021
NWS Storm Prediction Center Norman OK
1047 AM CST Sat Dec 11 2021

Areas affected...Southern AL into West-Central GA

Concerning...Severe potential...Watch possible 

Valid 111647Z - 111845Z

Probability of Watch Issuance...40 percent

SUMMARY...Potential exists from southwest AL into west-central GA
for a few stronger, more organized storms capable of damaging wind
gusts and/or a tornado or two.

DISCUSSION...Recent surface analysis places a well-defined cold
front from near RMG in northwest GA back southwestward across
central AL and southeast MS into eastern LA. Thunderstorms are
ongoing along this front from northwest GA into central AL, with
recent radar and satellite imagery also showing increasing
pre-frontal showers and thunderstorms from southern MS into southern
AL and the far western FL Panhandle. Modest buoyancy exists within
the pre-frontal corridor from southern MS into northwest/northern GA
and recent satellite imagery shows an increasingly agitated cumulus
field. Consequently, the current trend of increasing pre-frontal
storm coverage is likely to continue as broad ascent persists.
Relatively warm mid-level temperatures will likely limit updraft
depth and duration, evidenced by the limited lightning within the
pre-frontal development thus far. Even so, strong southwesterly flow
aloft atop slightly more southerly low-level flow results in both
strong deep-layer vertical shear as well as robust low-level
helicity. These environmental factors suggest that updraft
organization is possible within any storms that are able to
mature/persist, with damaging wind gusts and/or a tornado or two
possible.

..Mosier/Thompson.. 12/11/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FFC...BMX...MOB...

LAT...LON   31458840 32778683 33578560 33648449 32978450 31678600
            31028788 31458840

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 11, 2:00 AM CST	Mesoscale Discussion	SPC	Colbert, Franklin, Lauderdale, Lawrence, Limestone, Madison and 2 more	90 min
Dec 11, 3:15 AM CST	Mesoscale Discussion	SPC	Colbert, Franklin, Lauderdale, Marion	90 min
Dec 11, 3:41 AM CST	Tornado Watch	SPC	Colbert, Cullman, DeKalb, Fayette, Franklin, Jackson and 10 more	6 hr
Dec 11, 6:15 AM CST	Mesoscale Discussion	SPC	Cullman, Fayette, Franklin, Jackson, Lamar, Lawrence and 6 more	90 min
Dec 11, 7:34 AM CST	Mesoscale Discussion	SPC	Bibb, Blount, Calhoun, Cherokee, Clay, Cleburne and 8 more	86 min
Dec 11, 4:32 PM CST	Mesoscale Discussion	SPC	Bleckley, Burke, Columbia, Emanuel, Glascock, Houston and 10 more	88 min

Nearby

Mesoscale Discussions in Alabama, 2021 Mesoscale Discussions in Georgia, 2021 Every mesoscale discussion in 2021

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.