Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1506
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 7:20 PM CDT for 17 counties in Illinois; 5 counties in Kentucky; 7 counties in Missouri. It was in force for 85 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 7:20 PM CDT (00:20 UTC)
- Expired
- Aug 12, 2021, 8:45 PM CDT
- In force
- 85 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
All 29 counties
Alexander County, IL, Franklin County, IL, Gallatin County, IL, Hamilton County, IL, Hardin County, IL, Jackson County, IL, Jefferson County, IL, Johnson County, IL, Massac County, IL, Perry County, IL, Pope County, IL, Pulaski County, IL, Saline County, IL, Union County, IL, Wayne County, IL, White County, IL, Williamson County, IL, Ballard County, KY, Crittenden County, KY, Livingston County, KY, McCracken County, KY, Union County, KY, Bollinger County, MO, Cape Girardeau County, MO, Madison County, MO, Perry County, MO, Scott County, MO, Stoddard County, MO, Wayne County, MO
The radar
The Paducah radar (KPAH), 71 km from the middle of the area, began a volume at 00:22 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, 0.3 hours before the alert went out and 289 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
- 1786 J/kg
- Mixed-layer CIN
- -31 J/kg
- Mixed-layer LCL
- 1455 m above ground
- 0-6 km bulk shear
- 7 kt
- 0-1 km storm-relative helicity
- -25 m²/s²
- 0-3 km storm-relative helicity
- 0 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
659
ACUS11 KWNS 130021
SWOMCD
SPC MCD 130020
INZ000-KYZ000-ILZ000-MOZ000-130145-
Mesoscale Discussion 1506
NWS Storm Prediction Center Norman OK
0720 PM CDT Thu Aug 12 2021
Areas affected...Southeast MO...Southern IL...Far western KY
Concerning...Severe potential...Watch possible
Valid 130020Z - 130145Z
Probability of Watch Issuance...60 percent
SUMMARY...A damaging wind threat will continue this evening, though
a gradual weakening trend is expected with time.
DISCUSSION...A large thunderstorm cluster is moving southward across
central MO into extreme western IL at 0015Z, with the strongest
portion of the cluster located near St. Louis, where observed wind
gusts of 49-58 kt have been noted from observing sites in the area.
The greatest short-term damaging wind threat will likely remain with
this portion of the cluster, which will affect far southeast MO into
southern IL and far western KY through mid-evening.
While a weakening trend is eventually expected later this evening
due to weak vertical shear and increasing MLCINH, some damaging wind
threat is likely to be maintained for the next 2-3 hours before more
substantial boundary-layer cooling occurs. New watch issuance is
possible downstream by 01Z, depending on short-term observational
trends as the bowing segment approaches the edge of WW 434.
..Dean/Goss.. 08/13/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PAH...LSX...
LAT...LON 38338817 37638786 37318811 37018858 36838943 36778985
36799058 36809082 37489093 37619055 37818979 38148943
38468848 38338817SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 7:37 PM CDT | Severe Thunderstorm Watch | SPC | Alexander, Franklin, Gallatin, Hamilton, Hardin, Jackson and 10 more | 4 hr |
| Aug 12, 9:55 PM CDT | Mesoscale Discussion | SPC | Alexander, Franklin, Gallatin, Hamilton, Hardin, Johnson and 7 more | 95 min |
| Aug 13, 12:13 PM CDT | Mesoscale Discussion | SPC | Anderson, Bath, Boone, Bourbon, Boyd, Boyle and 55 more | 2 hr |
| Aug 12, 10:20 PM CDT | Mesoscale Discussion | SPC | Andrew, Atchison, Bates, Buchanan, Caldwell, Carroll and 18 more | 2 hr |
Nearby
Mesoscale Discussions in Illinois, 2021Mesoscale Discussions in Missouri, 2021Mesoscale Discussions in Kentucky, 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.