Alert archive / Tennessee / Mesoscale Discussions in 2021
Mesoscale Discussion 520
The Storm Prediction Center issued this mesoscale discussion at May 4, 2021, 4:17 AM CDT for 4 states. It was in force for 88 min.
The area
The outline as issued.
The facts
- Issued
- May 4, 2021, 4:17 AM CDT (09:17 UTC)
- Expired
- May 4, 2021, 5:45 AM CDT
- In force
- 88 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 140
All 84 counties
Crittenden County, AR, Massac County, IL, Adair County, KY, Allen County, KY, Ballard County, KY, Barren County, KY, Butler County, KY, Caldwell County, KY, Calloway County, KY, Christian County, KY, Crittenden County, KY, Cumberland County, KY, Edmonson County, KY, Graves County, KY, Grayson County, KY, Green County, KY, Hart County, KY, Hopkins County, KY, Livingston County, KY, Logan County, KY, Lyon County, KY, Marshall County, KY, McCracken County, KY, McLean County, KY, Metcalfe County, KY, Monroe County, KY, Muhlenberg County, KY, Ohio County, KY, Russell County, KY, Simpson County, KY, Todd County, KY, Trigg County, KY, Warren County, KY, Bedford County, TN, Benton County, TN, Cannon County, TN, Carroll County, TN, Cheatham County, TN, Chester County, TN, Clay County, TN, Coffee County, TN, Crockett County, TN, Davidson County, TN, Decatur County, TN, DeKalb County, TN, Dickson County, TN, Fayette County, TN, Franklin County, TN, Gibson County, TN, Giles County, TN, Hardeman County, TN, Hardin County, TN, Haywood County, TN, Henderson County, TN, Henry County, TN, Hickman County, TN, Houston County, TN, Humphreys County, TN, Jackson County, TN, Lawrence County, TN, Lewis County, TN, Lincoln County, TN, Macon County, TN, Madison County, TN, Marshall County, TN, Maury County, TN, McNairy County, TN, Montgomery County, TN, Moore County, TN, Perry County, TN, Putnam County, TN, Robertson County, TN, Rutherford County, TN, Shelby County, TN, Smith County, TN, Stewart County, TN, Sumner County, TN, Tipton County, TN, Trousdale County, TN, Warren County, TN, Wayne County, TN, Weakley County, TN, Williamson County, TN, Wilson County, TN
The radar
The Paducah radar (KPAH), 109 km from the middle of the area, began a volume at 09:20 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 00:00Z, 9.3 hours before the alert went out and 163 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
- 2263 J/kg
- Mixed-layer CIN
- -5 J/kg
- Mixed-layer LCL
- 1050 m above ground
- 0-6 km bulk shear
- 30 kt
- 0-1 km storm-relative helicity
- 119 m²/s²
- 0-3 km storm-relative helicity
- 193 m²/s²
- Significant tornado parameter
- 1.3
- Supercell composite
- 7.6
The text
As transmitted.
159
ACUS11 KWNS 040918
SWOMCD
SPC MCD 040917
KYZ000-TNZ000-ILZ000-ARZ000-MSZ000-041045-
Mesoscale Discussion 0520
NWS Storm Prediction Center Norman OK
0417 AM CDT Tue May 04 2021
Areas affected...western portions of Kentucky and Tennessee
Concerning...Severe Thunderstorm Watch 140...
Valid 040917Z - 041045Z
The severe weather threat for Severe Thunderstorm Watch 140
continues.
SUMMARY...Rick for primarily damaging winds continues locally across
WW 140. New WW may be needed east of the current watch, as storms
advance.
DISCUSSION...Latest radar loop shows a bowing band of storms moving
across far western portions of Kentucky and Tennessee at this time.
The strongest storms occurring in the vicinity of the
Kentucky/Tennessee border, where outflow continues to surge eastward
just to the south of a mesolow currently located between Cape
Girardeau and Paducah. Strong/locally damaging wind gusts remain
possible ahead of this portion of the line.
Meanwhile, some weakening of convection has occurred farther south
along the band, into southwestern Tennessee. Here, updrafts are
largely occurring just west of outflow at the leading edge of the
cold pool, in a slightly elevated manner.
Overall however, with the 06Z KBNA RAOB observing very steep lapse
rates aloft, above a shallow/stable boundary layer, continuation of
at least locally vigorous convection -- and associated potential for
strong/damaging gusts -- is expected over the next couple of hours
as storms advance eastward. A new WW may be needed as storms near
the eastern fringe of WW 140.
..Goss.. 05/04/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MRX...LMK...OHX...HUN...PAH...MEG...
LAT...LON 34979074 35648967 36498866 36938900 37318913 37718636
37218492 35078593 35038903 34979074SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 3, 8:38 PM CDT | Mesoscale Discussion | SPC | Arkansas, Baxter, Boone, Calhoun, Carroll, Clark and 60 more | 2 hr |
| May 3, 9:10 PM CDT | Severe Thunderstorm Watch | SPC | Baxter, Benton, Boone, Calhoun, Carroll, Clark and 50 more | 7 hr |
| May 3, 10:22 PM CDT | Mesoscale Discussion | SPC | Boone, Crawford, Franklin, Johnson, Madison, Marion and 2 more | 83 min |
| May 3, 11:34 PM CDT | Mesoscale Discussion | SPC | Baxter, Boone, Carroll, Clark, Cleburne, Conway and 27 more | 86 min |
| May 4, 1:06 AM CDT | Mesoscale Discussion | SPC | Clay, Craighead, Crittenden, Cross, Greene, Jackson and 5 more | 114 min |
| May 4, 1:41 AM CDT | Severe Thunderstorm Watch | SPC | Clay, Craighead, Crittenden, Cross, Greene, Mississippi and 2 more | 6 hr |
| May 4, 2:02 AM CDT | Mesoscale Discussion | SPC | Clay, Conway, Craighead, Cross, Faulkner, Garland and 16 more | 88 min |
| May 4, 6:44 AM CDT | Mesoscale Discussion | SPC | Bradley, Calhoun, Clark, Cleveland, Columbia, Dallas and 8 more | 2 hr |
| May 4, 10:52 AM CDT | Tornado Watch | SPC | Ashley, Bradley, Calhoun, Chicot, Columbia, Desha and 2 more | 7 hr |
| May 4, 11:58 AM CDT | Mesoscale Discussion | SPC | Crittenden, Lee, Phillips | 2 hr |
| May 4, 12:18 PM CDT | Severe Thunderstorm Watch | SPC | Phillips | 5 hr |
| May 4, 1:59 PM CDT | Mesoscale Discussion | SPC | Cleburne, Conway, Craighead, Cross, Faulkner, Greene and 17 more | 2 hr |
| May 3, 7:58 PM CDT | Severe Thunderstorm Watch | SPC | Clark, Clay, Crawford, Cumberland, Effingham, Jasper and 2 more | 3 hr |
| May 4, 1:17 AM CDT | Mesoscale Discussion | SPC | Adair, Allen, Barren, Butler, Christian, Clinton and 19 more | 118 min |
| May 4, 5:13 AM CDT | Severe Thunderstorm Watch | SPC | Adair, Allen, Barren, Butler, Clinton, Cumberland and 11 more | 5 hr |
| May 4, 7:31 AM CDT | Mesoscale Discussion | SPC | Anderson, Bedford, Bledsoe, Bradley, Campbell, Cannon and 33 more | 89 min |
| May 4, 8:37 AM CDT | Severe Thunderstorm Watch | SPC | Anderson, Blount, Bradley, Jefferson, Knox, Loudon and 7 more | 3 hr |
Nearby
Mesoscale Discussions in Tennessee, 2021Mesoscale Discussions in Kentucky, 2021Mesoscale Discussions in Arkansas, 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.