Alert archive / Mississippi / Mesoscale Discussions in 2021
Mesoscale Discussion 1553
The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2021, 1:20 PM CDT for 6 counties in Alabama; 20 counties in Mississippi; 19 counties in Tennessee. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 18, 2021, 1:20 PM CDT (18:20 UTC)
- Expired
- Aug 18, 2021, 3:45 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
All 45 counties
Colbert County, AL, Franklin County, AL, Lauderdale County, AL, Lawrence County, AL, Limestone County, AL, Marion County, AL, Alcorn County, MS, Benton County, MS, Calhoun County, MS, Chickasaw County, MS, DeSoto County, MS, Grenada 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, Tallahatchie County, MS, Tate County, MS, Tippah County, MS, Tishomingo County, MS, Union County, MS, Yalobusha County, MS, Bedford County, TN, Chester County, TN, Decatur County, TN, Fayette County, TN, Giles County, TN, Hardeman County, TN, Hardin County, TN, Henderson County, TN, Hickman County, TN, Lawrence County, TN, Lewis County, TN, Lincoln County, TN, Madison County, TN, Marshall County, TN, Maury County, TN, McNairy County, TN, Moore County, TN, Perry County, TN, Wayne County, TN
The radar
The Columbus AFB radar (KGWX), 100 km from the middle of the area, began a volume at 18:20 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 nearest sounding before it
Little Rock, AR (KLZK), launched 12:00Z, 6.3 hours before the alert went out and 119 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
- 1042 J/kg
- Mixed-layer CIN
- -18 J/kg
- Mixed-layer LCL
- 701 m above ground
- 0-6 km bulk shear
- 24 kt
- 0-1 km storm-relative helicity
- 37 m²/s²
- 0-3 km storm-relative helicity
- 46 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 1.1
The text
As transmitted.
396
ACUS11 KWNS 181820
SWOMCD
SPC MCD 181820
TNZ000-ALZ000-MSZ000-182045-
Mesoscale Discussion 1553
NWS Storm Prediction Center Norman OK
0120 PM CDT Wed Aug 18 2021
Areas affected...Northern Mississippi into northwest Alabama and
southwest Tennessee
Concerning...Severe potential...Watch unlikely
Valid 181820Z - 182045Z
Probability of Watch Issuance...5 percent
SUMMARY...Scattered thunderstorms may produce sporadic damaging
winds through the afternoon hours across parts of northern MS,
northwest AL, and southern TN.
DISCUSSION...A cluster of thunderstorms has shown signs of growth
and intensification over the past hour in the form of increased
lightning activity and cloud top cooling. While this activity is
rather disorganized, the downstream environment is destabilizing as
temperatures warm into the low 90s with dewpoints in the mid 70s.
MLCAPE values have already increased to 1000-1500 J/kg and may
increase further to near 2000 J/kg through the afternoon. Deep-layer
shear is modest over the region and will limit storm organization,
but amalgamating cold pools within the cluster and persistent ascent
associated with a weak shortwave trough over the region will likely
maintain thunderstorms into the early evening. Additional
thunderstorm development is possible along a weak confluence axis
noted in surface observations across the region. The combination of
moderate MLCAPE and somewhat steep low-level lapse rates (near 7
C/km) will support a damaging wind potential through the afternoon
and early evening both with the developing cluster and with any
stronger, more isolated cells. The overall severe potential is
expected to remain sporadic, so a watch is not anticipated at this
time.
..Moore/Dial.. 08/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OHX...BMX...HUN...MEG...JAN...
LAT...LON 34899025 35428941 35908828 35958707 35648645 35218622
34478682 34028801 33828896 33728976 33779036 34089066
34899025Nearby
Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Tennessee, 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.