Alert archive / Tennessee / Mesoscale Discussions in 2021
Mesoscale Discussion 575
The Storm Prediction Center issued this mesoscale discussion at May 9, 2021, 5:48 PM CDT for 4 states. It was in force for 87 min.
The area
The outline as issued.
The facts
- Issued
- May 9, 2021, 5:48 PM CDT (22:48 UTC)
- Expired
- May 9, 2021, 7:15 PM CDT
- In force
- 87 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 158
All 50 counties
Colbert County, AL, Franklin County, AL, Lauderdale County, AL, Lawrence County, AL, Limestone County, AL, Crittenden County, AR, Lee County, AR, Phillips County, AR, St. Francis County, AR, Alcorn County, MS, Benton County, MS, Coahoma County, MS, DeSoto County, MS, Itawamba County, MS, Lafayette County, MS, Lee County, MS, Marshall County, MS, Panola County, MS, Pontotoc County, MS, Prentiss County, MS, Quitman County, MS, Tate County, MS, Tippah County, MS, Tishomingo County, MS, Tunica County, MS, Union County, MS, Benton County, TN, Carroll County, TN, Chester County, TN, Crockett County, TN, Decatur County, TN, Fayette County, TN, Giles County, TN, Hardeman County, TN, Hardin County, TN, Haywood County, TN, Henderson County, TN, Hickman County, TN, Humphreys County, TN, Lawrence County, TN, Lewis County, TN, Madison County, TN, Marshall County, TN, Maury County, TN, McNairy County, TN, Perry County, TN, Shelby County, TN, Tipton County, TN, Wayne County, TN, Williamson County, TN
The radar
The Memphis radar (KNQA), 77 km from the middle of the area, began a volume at 22:51 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
Little Rock, AR (KLZK), launched 12:00Z, 10.8 hours before the alert went out and 89 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
- 203 J/kg
- Mixed-layer CIN
- -439 J/kg
- Mixed-layer LCL
- 759 m above ground
- 0-6 km bulk shear
- 26 kt
- 0-1 km storm-relative helicity
- 446 m²/s²
- 0-3 km storm-relative helicity
- 571 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
607
ACUS11 KWNS 092249
SWOMCD
SPC MCD 092248
TNZ000-ALZ000-MSZ000-ARZ000-100015-
Mesoscale Discussion 0575
NWS Storm Prediction Center Norman OK
0548 PM CDT Sun May 09 2021
Areas affected...Far Eastern Arkansas...Northern
Mississippi...Northwest Alabama...and Southwestern/Central Tennessee
Concerning...Severe Thunderstorm Watch 158...
Valid 092248Z - 100015Z
The severe weather threat for Severe Thunderstorm Watch 158
continues.
SUMMARY...Semi-discrete storms capable of large hail, damaging wind
gusts, and a few tornadoes remain possible this evening across WW
158.
DISCUSSION...Regional radar shows a segmented line of convection
moving southeast through WW 158, extending northeast into portions
of southwestern Tennessee. Storms thus far have been able to
maintain semi-discrete within the line, likely attributable to
strong deep layer shear (effective shear near 50 kt) and decent
low-level shear (20-25 kt 0-1 km shear) amid modest instability that
ranges from 2000 J/kg in northern Mississippi to near 1000 J/kg
across southwest Tennessee. In particular, mid-level lapse rates of
7-8 C in the 700-500 mb layer will continue to support a large hail
threat, as indicated in RAP forecast soundings.
Given the persistence of the semi-discrete mode in the short term,
embedded supercells capable of large hail, damaging wind gusts, and
a few tornadoes will remain possible during the next couple of
hours. As the low-level jet begins to strengthen this evening,
increasing low-level theta-e advection and destabilization should
allow storms to transition to a linear mode after the 00z-01z time
frame. Given uncertainty in convective evolution the next few hours,
downstream watch issuance across portions of central Tennessee and
northwest Alabama remains unclear, and thus, trends will continue to
be monitored.
..Karstens.. 05/09/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OHX...BMX...HUN...MEG...JAN...LZK...
LAT...LON 35449034 35868940 36188778 36108684 35358659 34508707
34168841 34109065 34489129 35129094 35449034SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 9, 3:23 PM CDT | Mesoscale Discussion | SPC | DeKalb, Jackson, Lawrence, Limestone, Madison, Morgan | 2 hr |
| May 9, 3:46 AM CDT | Mesoscale Discussion | SPC | Baxter, Boone, Carroll, Fulton, Izard, Madison and 4 more | 119 min |
| May 9, 12:14 PM CDT | Mesoscale Discussion | SPC | Arkansas, Ashley, Bradley, Calhoun, Chicot, Clark and 46 more | 91 min |
| May 9, 1:14 PM CDT | Severe Thunderstorm Watch | SPC | Arkansas, Ashley, Bradley, Calhoun, Chicot, Clark and 33 more | 8 hr |
| May 9, 2:27 PM CDT | Severe Thunderstorm Watch | SPC | Craighead, Crittenden, Cross, Lee, Mississippi, Phillips and 2 more | 7 hr |
| May 9, 3:42 PM CDT | Mesoscale Discussion | SPC | Arkansas, Ashley, Bradley, Calhoun, Clark, Cleveland and 31 more | 93 min |
| May 9, 5:41 PM CDT | Mesoscale Discussion | SPC | Arkansas, Ashley, Bradley, Calhoun, Chicot, Clark and 16 more | 2 hr |
| May 9, 3:53 PM CDT | Mesoscale Discussion | SPC | Claiborne, Copiah, Covington, Hinds, Jasper, Jefferson and 10 more | 2 hr |
| May 9, 6:40 PM CDT | Mesoscale Discussion | SPC | Calhoun, Chickasaw, Itawamba, Lafayette, Lee, Monroe and 3 more | 65 min |
Nearby
Mesoscale Discussions in Tennessee, 2021Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Alabama, 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.