Alert archive / Alabama / Mesoscale Discussions in 2021
Mesoscale Discussion 340
The Storm Prediction Center issued this mesoscale discussion at Apr 9, 2021, 11:44 AM CDT for 34 counties in Alabama; Heard County, Troup County, Georgia; 9 counties in Mississippi. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 9, 2021, 11:44 AM CDT (16:44 UTC)
- Expired
- Apr 9, 2021, 1:45 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 45 counties
Autauga County, AL, Bibb County, AL, Blount County, AL, Calhoun County, AL, Chambers County, AL, Chilton County, AL, Clay County, AL, Coosa County, AL, Cullman County, AL, Dallas County, AL, Elmore County, AL, Fayette County, AL, Greene County, AL, Hale County, AL, Jefferson County, AL, Lamar County, AL, Lee County, AL, Lowndes County, AL, Macon County, AL, Marengo County, AL, Marion County, AL, Montgomery County, AL, Perry County, AL, Pickens County, AL, Randolph County, AL, Russell County, AL, Shelby County, AL, St. Clair County, AL, Sumter County, AL, Talladega County, AL, Tallapoosa County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL, Heard County, GA, Troup County, GA, Clay County, MS, Kemper County, MS, Lauderdale County, MS, Lowndes County, MS, Monroe County, MS, Neshoba County, MS, Noxubee County, MS, Oktibbeha County, MS, Winston County, MS
The radar
The Birmingham radar (KBMX), 38 km from the middle of the area, began a volume at 16:46 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 12:00Z, 4.7 hours before the alert went out and 37 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
- 89 J/kg
- Mixed-layer CIN
- -208 J/kg
- Mixed-layer LCL
- 1321 m above ground
- 0-6 km bulk shear
- 44 kt
- 0-1 km storm-relative helicity
- 70 m²/s²
- 0-3 km storm-relative helicity
- 141 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.0
The text
As transmitted.
239
ACUS11 KWNS 091645
SWOMCD
SPC MCD 091644
GAZ000-ALZ000-MSZ000-091845-
Mesoscale Discussion 0340
NWS Storm Prediction Center Norman OK
1144 AM CDT Fri Apr 09 2021
Areas affected...Parts of central Alabama and adjacent portions of
eastern Mississippi and western Georgia
Concerning...Severe potential...Watch possible
Valid 091644Z - 091845Z
Probability of Watch Issuance...40 percent
SUMMARY...Scattered, intensifying thunderstorm development appears
possible by 1-3 PM CDT, posing increasing potential for large,
possibly damaging hail. It is not yet certain a severe weather
watch will be needed, but trends will continue to be monitored for
this possibility.
DISCUSSION...Daytime heating of a deepening moist boundary layer,
beneath the eastern fringes of plume of warm elevated mixed-layer
air is contributing to moderately large mixed layer CAPE across much
of central Alabama and surrounding areas. Mid-level inhibition
appears relatively weak, and various model output indicates the
initiation of increasing scattered thunderstorm development is
possible by 18-20Z. Mid/upper support for this is unclear, but much
of the region is under the influence of at least broad, weak
low-level warm advection.
Low-level wind fields are modest to weak, but westerly flow on the
order of 30-40+ kt may persist and contribute to sufficient
deep-layer shear for supercell structures posing a risk for severe
hail. Some of this could become fairly large, given the
thermodynamic profiles. It is possible an eventual consolidation of
storms could lead to an upscale growing and organizing cluster of
storms posing increasing potential for damaging wind gusts.
..Kerr/Thompson.. 04/09/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...FFC...BMX...HUN...MOB...MEG...JAN...
LAT...LON 33998893 34258727 33828576 33218490 32148510 32118651
31928790 32498921 33998893SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 9, 2:49 AM CDT | Mesoscale Discussion | SPC | Baldwin, Mobile | 2 hr |
| Apr 9, 7:38 AM CDT | Mesoscale Discussion | SPC | Autauga, Barbour, Bullock, Butler, Chambers, Clarke and 17 more | 3 hr |
| Apr 9, 12:54 PM CDT | Severe Thunderstorm Watch | SPC | Autauga, Bibb, Blount, Chilton, Coosa, Dallas and 19 more | 7 hr |
| Apr 9, 5:54 PM CDT | Mesoscale Discussion | SPC | Fayette, Greene, Lamar, Marion, Pickens, Sumter and 2 more | 96 min |
| Apr 9, 1:25 PM CDT | Mesoscale Discussion | SPC | Bolivar, Coahoma, DeSoto, Grenada, Humphreys, Issaquena and 9 more | 95 min |
| Apr 9, 3:10 PM CDT | Mesoscale Discussion | SPC | Bolivar, Carroll, Coahoma, DeSoto, Grenada, Humphreys and 12 more | 95 min |
| Apr 9, 3:42 PM CDT | Severe Thunderstorm Watch | SPC | Alcorn, Attala, Benton, Bolivar, Calhoun, Carroll and 52 more | 7 hr |
| Apr 9, 6:14 PM CDT | Mesoscale Discussion | SPC | Attala, Calhoun, Carroll, Chickasaw, Choctaw, Clay and 23 more | 3 hr |
Nearby
Mesoscale Discussions in Alabama, 2021Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Georgia, 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.