Alert archive / Tennessee / Mesoscale Discussions in 2021
Mesoscale Discussion 257
The Storm Prediction Center issued this mesoscale discussion at Mar 25, 2021, 2:29 PM CDT for Alcorn County, Mississippi; 22 counties in Tennessee. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Mar 25, 2021, 2:29 PM CDT (19:29 UTC)
- Expired
- Mar 25, 2021, 4:30 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...tornado watch likely
- Chance of a watch
- 80%
All 23 counties
Alcorn County, MS, Bedford County, TN, Benton County, TN, Cannon County, TN, Cheatham County, TN, Chester County, TN, Davidson County, TN, Decatur County, TN, DeKalb County, TN, Dickson County, TN, Hardin County, TN, Henderson County, TN, Hickman County, TN, Humphreys County, TN, Lewis County, TN, Marshall County, TN, Maury County, TN, McNairy County, TN, Perry County, TN, Rutherford County, TN, Smith County, TN, Williamson County, TN, Wilson County, TN
The radar
The Nashville radar (KOHX), 131 km from the middle of the area, began a volume at 19:31 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
Nashville Metro, TN (KBNA), launched 12:00Z, 7.5 hours before the alert went out and 120 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
- 60 J/kg
- Mixed-layer CIN
- -88 J/kg
- Mixed-layer LCL
- 753 m above ground
- 0-6 km bulk shear
- 57 kt
- 0-1 km storm-relative helicity
- 168 m²/s²
- 0-3 km storm-relative helicity
- 113 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
517
ACUS11 KWNS 251930
SWOMCD
SPC MCD 251929
TNZ000-ALZ000-MSZ000-252130-
Mesoscale Discussion 0257
NWS Storm Prediction Center Norman OK
0229 PM CDT Thu Mar 25 2021
Areas affected...far northern Mississippi into Middle Tennessee
Concerning...Severe potential...Tornado Watch likely
Valid 251929Z - 252130Z
Probability of Watch Issuance...80 percent
SUMMARY...The threat of severe storms including tornadoes will
increase by late afternoon into Middle Tennessee and persist through
the evening. A watch may be issued by 21Z.
DISCUSSION...Surface analysis currently shows a warm front into far
southwestern TN extending east/southeast into northern AL.
Meanwhile, another warm front extended from the developing surface
low from southern IL into central KY.
In between these two fronts, gradual warming is taking place, with
temperatures now into the low 70s F. MUCAPE currently remains below
1000 J/kg as a result of dewpoints near 60 F.
Strengthening 850 mb winds out of the southwest later today should
aid moisture advection out of MS into Middle TN, with areas of
heating helping to destabilize as well. Shear will become
increasingly favorable for tornadic supercells in the 21-03Z time
frame, and a few tornadoes are anticipated as the mid 60s F
dewpoints arrive later today. With the more unstable air in place,
effective SRH may reach 400-500 m2/s2.
..Jewell/Hart.. 03/25/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OHX...HUN...MEG...
LAT...LON 35048892 35238887 35668872 36178799 36478647 36318583
36008560 35548590 35368661 35378741 35278780 34998804
34718875 34798891 35048892SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 24, 9:25 PM CDT | Mesoscale Discussion | SPC | Adams, Amite, Claiborne, Clarke, Copiah, Covington and 27 more | 65 min |
| Mar 25, 9:02 AM CDT | Mesoscale Discussion | SPC | Itawamba, Lee, Lowndes, Monroe, Prentiss, Tishomingo | 118 min |
| Mar 25, 10:12 AM CDT | Mesoscale Discussion | SPC | Kemper, Lauderdale, Lowndes, Noxubee | 3 hr |
| Mar 25, 10:58 AM CDT | Mesoscale Discussion | SPC | Alcorn, Attala, Benton, Calhoun, Carroll, Chickasaw and 35 more | 3 hr |
| Mar 25, 11:00 AM CDT | Mesoscale Discussion | SPC | Hancock, Harrison, Pearl River, Stone | 2 hr |
| Mar 25, 11:26 AM CDT | Tornado Watch | SPC | Attala, Calhoun, Carroll, Chickasaw, Choctaw, Clarke and 40 more | 9 hr |
| Mar 25, 1:24 PM CDT | Mesoscale Discussion | SPC | Chickasaw, Choctaw, Clarke, Clay, Itawamba, Jasper and 16 more | 2 hr |
| Mar 25, 3:45 PM CDT | Mesoscale Discussion | SPC | Clarke, Covington, Forrest, Jasper, Jones, Lamar and 3 more | 2 hr |
| Mar 25, 3:48 PM CDT | Tornado Watch | SPC | Alcorn | 7 hr |
| Mar 25, 2:33 PM CDT | Mesoscale Discussion | SPC | Dyer, Henry, Lake, Obion, Weakley | 117 min |
| Mar 25, 4:31 PM CDT | Mesoscale Discussion | SPC | Bledsoe, Blount, Bradley, Hamilton, Loudon, McMinn and 5 more | 119 min |
| Mar 25, 5:52 PM CDT | Mesoscale Discussion | SPC | Benton, Carroll, Cheatham, Chester, Crockett, Davidson and 24 more | 83 min |
Nearby
Mesoscale Discussions in Tennessee, 2021Mesoscale Discussions in Mississippi, 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.