Alert archive / Alabama / Mesoscale Discussions in 2021
Mesoscale Discussion 296
The Storm Prediction Center issued this mesoscale discussion at Mar 28, 2021, 4:56 AM CDT for 6 counties in Alabama; 5 counties in Georgia; Bradley County, Tennessee. It was in force for 94 min.
The area
The outline as issued.
The facts
- Issued
- Mar 28, 2021, 4:56 AM CDT (09:56 UTC)
- Expired
- Mar 28, 2021, 6:30 AM CDT
- In force
- 94 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 65
Counties Blount County, AL, Cullman County, AL, DeKalb County, AL, Etowah County, AL, Marshall County, AL, Walker County, AL, Catoosa County, GA, Chattooga County, GA, Dade County, GA, Walker County, GA, Whitfield County, GA, Bradley County, TN
The radar
The Northeast Alabama radar (KHTX), 82 km from the middle of the area, began a volume at 09:55 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, 9.9 hours before the alert went out and 123 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.
- Mixed-layer CAPE
- 643 J/kg
- Mixed-layer CIN
- -22 J/kg
- Mixed-layer LCL
- 1359 m above ground
- 0-6 km bulk shear
- 52 kt
- 0-1 km storm-relative helicity
- 126 m²/s²
- 0-3 km storm-relative helicity
- 152 m²/s²
- Significant tornado parameter
- 0.3
- Supercell composite
- 3.7
The text
As transmitted.
497
ACUS11 KWNS 280956
SWOMCD
SPC MCD 280956
TNZ000-GAZ000-ALZ000-281130-
Mesoscale Discussion 0296
NWS Storm Prediction Center Norman OK
0456 AM CDT Sun Mar 28 2021
Areas affected...Parts of north central/northeastern Alabama into
adjacent portions of the southern Appalachians vicinity
Concerning...Tornado Watch 65...
Valid 280956Z - 281130Z
The severe weather threat for Tornado Watch 65 continues.
SUMMARY...A risk for locally severe wind gusts and perhaps an
isolated brief tornado may continue in stronger cells within a
squall line overspreading the region through 7-9 AM EDT.
DISCUSSION...Warmer mid-level air, associated with the subtropical
ridge, still appears to be confining stronger convection to northern
portions of Alabama northward, with the most vigorous storms on the
southern flank, aided by better boundary-layer instability across
northern Alabama. North/northeast of Chattanooga, TN,
boundary-layer warming and moistening has been slower to occur that
suggested by NAM/Rapid Refresh forecast soundings, and the
convective line may spread into the lee of the southern Appalachians
by or shortly after daybreak, before substantive boundary-layer
moistening can occur there.
However, the squall line has become closely aligned with a belt of
seasonably strong southwesterly deep-layer ambient mean flow in
excess of 60 kts, including 50-60 around 850 mb. Associated
momentum and low-level shear probably will continue to support a
risk for locally severe wind gusts, and/or perhaps a brief tornado,
as the line progresses across the remainder of northern Alabama into
portions of adjacent northwest Georgia and southeastern Tennessee
through 12-13z.
..Kerr.. 03/28/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MRX...FFC...BMX...HUN...
LAT...LON 33898758 34568636 35448451 34938470 34098561 33538702
33588772 33898758SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 27, 10:45 PM CDT | Mesoscale Discussion | SPC | Colbert, Franklin, Lauderdale, Lawrence, Limestone, Madison and 3 more | 90 min |
| Mar 27, 11:27 PM CDT | Tornado Watch | SPC | Blount, Colbert, Cullman, DeKalb, Fayette, Franklin and 11 more | 8 hr |
| Mar 28, 1:25 AM CDT | Mesoscale Discussion | SPC | Jackson | 2 hr |
| Mar 28, 1:57 AM CDT | Mesoscale Discussion | SPC | Blount, Colbert, Cullman, DeKalb, Etowah, Fayette and 11 more | 93 min |
| Mar 28, 5:10 AM CDT | Severe Thunderstorm Watch | SPC | Bibb, Blount, Calhoun, Cherokee, Clay, Cleburne and 12 more | 5 hr |
| Mar 28, 7:29 AM CDT | Mesoscale Discussion | SPC | Calhoun, Cleburne, Talladega | 91 min |
| Mar 28, 9:14 AM CDT | Mesoscale Discussion | SPC | Autauga, Chambers, Chilton, Clay, Coosa, Dallas and 6 more | 61 min |
| Mar 28, 11:38 AM CDT | Mesoscale Discussion | SPC | Baldwin, Bibb, Bleckley, Burke, Butts, Columbia and 34 more | 3 hr |
| Mar 28, 4:51 PM CDT | Mesoscale Discussion | SPC | Appling, Atkinson, Bacon, Baker, Ben Hill, Berrien and 46 more | 54 min |
| Mar 27, 8:42 PM CDT | Mesoscale Discussion | SPC | Chester, Fayette, Hardeman, Hardin, McNairy, Shelby | 93 min |
| Mar 27, 9:01 PM CDT | Tornado Watch | SPC | Chester, Crockett, Decatur, Fayette, Hardeman, Hardin and 9 more | 7 hr |
| Mar 28, 2:07 AM CDT | Severe Thunderstorm Watch | SPC | Anderson, Bledsoe, Blount, Bradley, Cumberland, Hamilton and 14 more | 6 hr |
Nearby
Mesoscale Discussions in Alabama, 2021Mesoscale Discussions in Georgia, 2021Mesoscale Discussions in Tennessee, 2021Every 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.