Alert archive / Tennessee / Mesoscale Discussions in 2018
Mesoscale Discussion 1749
The Storm Prediction Center issued this mesoscale discussion at Dec 31, 2018, 1:54 PM CST for 16 counties in Alabama; 13 counties in Mississippi; 21 counties in Tennessee. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Dec 31, 2018, 1:54 PM CST (19:54 UTC)
- Expired
- Dec 31, 2018, 4:00 PM CST
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
All 50 counties
Colbert County, AL, Fayette County, AL, Franklin County, AL, Greene County, AL, Lamar County, AL, Lauderdale County, AL, Lawrence County, AL, Limestone County, AL, Madison County, AL, Marion County, AL, Morgan County, AL, Pickens County, AL, Sumter County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL, Clarke County, MS, Jasper County, MS, Kemper County, MS, Lauderdale County, MS, Lowndes County, MS, Monroe County, MS, Neshoba County, MS, Newton County, MS, Noxubee County, MS, Oktibbeha County, MS, Scott County, MS, Smith County, MS, Winston County, MS, Bedford County, TN, Cheatham County, TN, Davidson County, TN, Dickson County, TN, Giles County, TN, Hickman County, TN, Lawrence County, TN, Lewis County, TN, Lincoln County, TN, Macon County, TN, Marshall County, TN, Maury County, TN, Montgomery County, TN, Moore County, TN, Robertson County, TN, Rutherford County, TN, Sumner County, TN, Trousdale County, TN, Wayne County, TN, Williamson County, TN, Wilson County, TN
The radar
The Columbus AFB radar (KGWX), 78 km from the middle of the area, began a volume at 19:54 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, 7.9 hours before the alert went out and 154 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
- 27 J/kg
- Mixed-layer CIN
- -137 J/kg
- Mixed-layer LCL
- 572 m above ground
- 0-6 km bulk shear
- 54 kt
- 0-1 km storm-relative helicity
- 264 m²/s²
- 0-3 km storm-relative helicity
- 336 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
439
ACUS11 KWNS 311955
SWOMCD
SPC MCD 311954
TNZ000-ALZ000-MSZ000-312200-
Mesoscale Discussion 1749
NWS Storm Prediction Center Norman OK
0154 PM CST Mon Dec 31 2018
Areas affected...Middle Tennessee...northwest and west central
Alabama...and into eastern Mississippi
Concerning...Tornado Watch 449...
Valid 311954Z - 312200Z
The severe weather threat for Tornado Watch 449 continues.
SUMMARY...Local severe risk -- including the potential for a brief
tornado or two -- continues across the watch area.
DISCUSSION...Latest radar loop shows a band of storms moving across
the Mid South and central Gulf Coast states, with the stronger/more
organized portion of the band to the north, and increasingly
disorganized/weaker storms farther south.
This stronger portion of the band, crossing Middle Tennessee, far
northwest Alabama, and northeast Mississippi, is a fairly organized
QLCS, though it remains low-topped to the degree that little
lightning is being observed.
Still, with strong shear in place across the region (flow increasing
with height to in excess of 50kt between .5km and 1km AGL, and to
near 100kt at mid levels), risk for locally damaging wind gusts, and
a brief tornado or two, will continue as convection continues moving
quickly eastward across the area.
As storms advance farther eastward, toward eastern Tennessee and
northeast Alabama over the next couple of hours, indications of even
more limited instability with eastward extent suggest that an
additional watch, to the east of Tornado Watch 449 -- may not be
required.
..Goss.. 12/31/2018
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OHX...BMX...HUN...MOB...MEG...JAN...
LAT...LON 36598595 35478612 33698712 32008847 31698987 32428976
34038846 36608741 36598595SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 31, 11:22 AM CST | Mesoscale Discussion | SPC | Colbert, Franklin, Lamar, Lauderdale, Marion | 83 min |
| Dec 31, 11:47 AM CST | Tornado Watch | SPC | Colbert, Cullman, Fayette, Franklin, Greene, Lamar and 11 more | 5 hr |
| Dec 31, 7:02 AM CST | Mesoscale Discussion | SPC | Adams, Amite, Attala, Choctaw, Claiborne, Copiah and 26 more | 118 min |
Nearby
Mesoscale Discussions in Tennessee, 2018Mesoscale Discussions in Alabama, 2018Mesoscale Discussions in Mississippi, 2018Every mesoscale discussion in 2018
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.