Alert archive / Alabama / Mesoscale Discussions in 2021

Mesoscale Discussion 264

March 25, 202138 counties in Alabama; 5 counties in Tennessee

The Storm Prediction Center issued this mesoscale discussion at Mar 25, 2021, 7:00 PM CDT for 38 counties in Alabama; 5 counties in Tennessee. It was in force for 30 min.

The area

The outline as issued.

The facts

Issued: Mar 25, 2021, 7:00 PM CDT (00:00 UTC)
Expired: Mar 25, 2021, 7:30 PM CDT
In force: 30 min
Issued by: the Storm Prediction Center
Concerning: Tornado watch 50

All 43 counties

Autauga County, AL, Bibb County, AL, Blount County, AL, Calhoun County, AL, Cherokee County, AL, Chilton County, AL, Clay County, AL, Cleburne County, AL, Colbert County, AL, Coosa County, AL, Cullman County, AL, Dallas County, AL, DeKalb County, AL, Etowah County, AL, Fayette County, AL, Franklin County, AL, Greene County, AL, Hale County, AL, Jackson County, AL, Jefferson County, AL, Lamar County, AL, Lauderdale County, AL, Lawrence County, AL, Limestone County, AL, Madison County, AL, Marengo County, AL, Marion County, AL, Marshall County, AL, Morgan County, AL, Perry County, AL, Pickens County, AL, Shelby County, AL, St. Clair County, AL, Sumter County, AL, Talladega County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL, Franklin County, TN, Giles County, TN, Lawrence County, TN, Lincoln County, TN, Wayne County, TN

The radar

The Birmingham radar (KBMX), 49 km from the middle of the area, began a volume at 00:02 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.

The nearest sounding before it

Birmingham, AL (KBMX), launched 00:00Z, 0.0 hours before the alert went out and 48 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: 1313 J/kg
Mixed-layer CIN: -13 J/kg
Mixed-layer LCL: 662 m above ground
0-6 km bulk shear: 68 kt
0-1 km storm-relative helicity: 341 m²/s²
0-3 km storm-relative helicity: 334 m²/s²
Significant tornado parameter: 3.1
Supercell composite: 13.2

Open this sounding in Storm Lab

The text

As transmitted.

030 
ACUS11 KWNS 260001
SWOMCD
SPC MCD 260000 
ALZ000-TNZ000-260030-

Mesoscale Discussion 0264
NWS Storm Prediction Center Norman OK
0700 PM CDT Thu Mar 25 2021

Areas affected...central and northern AL...southern middle TN

Concerning...Tornado Watch 50...

Valid 260000Z - 260030Z

The severe weather threat for Tornado Watch 50 continues.

SUMMARY...A new tornado watch will likely be issued by 730-745pm CDT
and effectively replace the ongoing PDS tornado watch set to expire
at 800pm CDT.

DISCUSSION...Radar mosaic shows several clusters of storms across AL
and a band of storms near the TN/MS/AL border as of 7pm CDT. 
Although a considerable amount of convection has led to rain-cooled
temperatures and a reduction in instability over north-central and
northern AL, a moist and adequately unstable airmass remains in
place given the presence of mid 60s dewpoints near the TN border to
upper 60s over south-central AL.  Very strong low to mid-level flow
will conditionally support updraft rotation with established/mature
updrafts.  It appears the overall severe risk has lessened compared
to earlier this afternoon, but isolated large hail, damaging gusts,
and a tornado threat will probably persist through much of the
evening.  It is unclear whether more than a few storms will pose a
severe risk, but the environment will at least favor some potential
for severe.

..Smith/Grams.. 03/26/2021

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

ATTN...WFO...MRX...OHX...BMX...HUN...MOB...

LAT...LON   33108829 35288792 35248574 33828544 32818589 32018776
            32008835 33108829

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Mar 25, 7:47 PM CDT	Tornado Watch	SPC	Autauga, Bibb, Calhoun, Chambers, Chilton, Clay and 18 more	3 hr
Mar 25, 7:57 PM CDT	Tornado Watch	SPC	Colbert, DeKalb, Franklin, Jackson, Lauderdale, Lawrence and 4 more	3 hr
Mar 25, 9:04 PM CDT	Mesoscale Discussion	SPC	Coosa, Randolph, Tallapoosa	56 min
Mar 25, 7:36 PM CDT	Mesoscale Discussion	SPC	Bedford, Cannon, Coffee, Davidson, DeKalb, Grundy and 11 more	84 min
Mar 25, 9:07 PM CDT	Mesoscale Discussion	SPC	Bedford, Bledsoe, Cannon, Clay, Coffee, Cumberland and 18 more	83 min
Mar 25, 9:26 PM CDT	Tornado Watch	SPC	Anderson, Bledsoe, Bradley, Campbell, Cumberland, Fentress and 14 more	2 hr

Nearby

Mesoscale Discussions in Alabama, 2021 Mesoscale Discussions in Tennessee, 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.