Alert archive / Alabama / Mesoscale Discussions in 2021
Mesoscale Discussion 2075
The Storm Prediction Center issued this mesoscale discussion at Dec 29, 2021, 2:36 PM CST for 22 counties in Alabama; 5 counties in Georgia; 8 counties in Tennessee. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Dec 29, 2021, 2:36 PM CST (20:36 UTC)
- Expired
- Dec 29, 2021, 5:00 PM CST
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch likely
- Chance of a watch
- 80%
All 35 counties
Blount County, AL, Calhoun County, AL, Cherokee County, AL, Colbert County, AL, Cullman County, AL, DeKalb County, AL, Etowah County, AL, Fayette County, AL, Franklin County, AL, Jackson County, AL, Jefferson County, AL, Lamar County, AL, Lauderdale County, AL, Lawrence County, AL, Limestone County, AL, Madison County, AL, Marion County, AL, Marshall County, AL, Morgan County, AL, St. Clair County, AL, Walker County, AL, Winston County, AL, Catoosa County, GA, Chattooga County, GA, Dade County, GA, Floyd County, GA, Walker County, GA, Franklin County, TN, Giles County, TN, Lawrence County, TN, Lincoln County, TN, Marion County, TN, Marshall County, TN, Moore County, TN, Wayne County, TN
The radar
The Northeast Alabama radar (KHTX), 64 km from the middle of the area, began a volume at 20:37 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, 8.6 hours before the alert went out and 146 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 690 m above ground
- 0-6 km bulk shear
- 36 kt
- 0-1 km storm-relative helicity
- 75 m²/s²
- 0-3 km storm-relative helicity
- 103 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
595
ACUS11 KWNS 292036
SWOMCD
SPC MCD 292036
GAZ000-TNZ000-ALZ000-MSZ000-292300-
Mesoscale Discussion 2075
NWS Storm Prediction Center Norman OK
0236 PM CST Wed Dec 29 2021
Areas affected...portions of Middle TN...northern AL and northwest
GA
Concerning...Severe potential...Watch likely
Valid 292036Z - 292300Z
Probability of Watch Issuance...80 percent
SUMMARY...Severe thunderstorm potential will increase from late
afternoon into this evening. Timing of watch issuance remains
uncertain, but may be needed within the next 2-3 hours.
DISCUSSION...Airmass recovery slowly continues this afternoon across
parts of northern AL in the wake of morning/early afternoon showers.
A surface boundary related to this earlier precipitation extends
west to east from roughly Haleyville AL into far northwest GA. Some
additional destabilization is expected with northward extent across
the MCD area in a sustained warm advection regime through the
evening hours. However, latest hi-res guidance continues to indicate
some uncertainty with regards to the northward extent of severe
potential, as well as in timing of the severe threat. Most guidance,
along with observational trends, preclude discrete warm sector
development in deference to an eastward-advancing, and currently
developing, bow/QLCS in the vicinity of the Mississippi
River/western TN/northwest MS as of 2030z/230pm CST. The best
estimate of severe storms moving into the MCD area is between
22-00z.
Once storms do emerge over the region, a strong low-level jet and
bowing segments will favor damaging gusts, with a few mesovortex
tornadoes possible as well. Convective trends will continue to be
monitored as a watch will likely be needed for portions of the MCD
area in the next 2-3 hours.
..Leitman/Hart.. 12/29/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MRX...FFC...OHX...BMX...HUN...MEG...JAN...
LAT...LON 33818564 33508679 33418766 33538812 33708824 34248826
35018822 35338794 35498757 35548706 35448624 35328552
35138516 34848500 34538496 34348502 34198514 33888544
33818564SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 29, 10:44 AM CST | Mesoscale Discussion | SPC | Colbert, Franklin, Lamar, Marion | 2 hr |
| Dec 29, 12:24 PM CST | Mesoscale Discussion | SPC | Geneva, Houston | 96 min |
| Dec 29, 3:53 PM CST | Tornado Watch | SPC | Bibb, Blount, Calhoun, Cherokee, Colbert, Cullman and 24 more | 6 hr |
| Dec 29, 4:38 PM CST | Mesoscale Discussion | SPC | Colbert, Fayette, Franklin, Lamar, Lauderdale, Lawrence and 6 more | 2 hr |
| Dec 29, 12:05 PM CST | Tornado Watch | SPC | Fayette, Hardeman, Hardin, McNairy, Shelby | 7 hr |
| Dec 29, 3:41 PM CST | Mesoscale Discussion | SPC | Hardeman, Hardin, McNairy | 64 min |
Nearby
Mesoscale Discussions in Alabama, 2021Mesoscale Discussions in Tennessee, 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.