Alert archive / Missouri / Mesoscale Discussions in 2021
Mesoscale Discussion 1505
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 6:06 PM CDT for 5 counties in Illinois; 8 counties in Missouri. It was in force for 84 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 6:06 PM CDT (23:06 UTC)
- Expired
- Aug 12, 2021, 7:30 PM CDT
- In force
- 84 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 434
Counties Calhoun County, IL, Jersey County, IL, Madison County, IL, Monroe County, IL, Saint Clair County, IL, City of Saint Louis, MO, Franklin County, MO, Gasconade County, MO, Jefferson County, MO, Lincoln County, MO, Saint Charles County, MO, Saint Louis County, MO, Warren County, MO
The radar
The St Louis radar (KLSX), 40 km from the middle of the area, began a volume at 23:04 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
Lincoln, IL (KILX), launched 12:00Z, 11.1 hours before the alert went out and 274 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
- 1191 J/kg
- Mixed-layer CIN
- -177 J/kg
- Mixed-layer LCL
- 1149 m above ground
- 0-6 km bulk shear
- 32 kt
- 0-1 km storm-relative helicity
- 140 m²/s²
- 0-3 km storm-relative helicity
- 128 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 3.1
The text
As transmitted.
352
ACUS11 KWNS 122306
SWOMCD
SPC MCD 122306
ILZ000-MOZ000-130030-
Mesoscale Discussion 1505
NWS Storm Prediction Center Norman OK
0606 PM CDT Thu Aug 12 2021
Areas affected...East-central MO into western IL
Concerning...Severe Thunderstorm Watch 434...
Valid 122306Z - 130030Z
The severe weather threat for Severe Thunderstorm Watch 434
continues.
SUMMARY...A damaging wind swath will be possible through 00-01Z in
association with a small bowing cluster.
DISCUSSION...At 23Z, a loosely-organized thunderstorm cluster and an
associated surging outflow was moving southeastward across
east-central MO and far western IL, while another outflow was
dropping southward in advance of the cluster. While vertical shear
is weak across the region, the strong cold pool and renewed
convective development along multiple outflow boundaries will likely
maintain a short-term damaging wind threat into the St. Louis area
and adjacent portions of western IL through 00-01Z.
With time, the combining outflows will likely continue surging
southward into this evening, potentially maintaining some damaging
wind risk into southeast MO and southwest IL, even as convection
eventually becomes more disorganized with time due to weak vertical
shear and increasing MLCINH.
..Dean.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LSX...SGF...
LAT...LON 38009042 38029132 38179178 38349178 39239083 38958978
38068982 38009042SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 11, 7:35 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 20 more | 85 min |
| Aug 11, 8:22 PM CDT | Severe Thunderstorm Watch | SPC | Bureau, Cook, DeKalb, DuPage, Ford, Grundy and 11 more | 8 hr |
| Aug 11, 11:06 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 15 more | 84 min |
| Aug 12, 3:16 AM CDT | Mesoscale Discussion | SPC | Bureau, Ford, Fulton, Grundy, Iroquois, Kankakee and 16 more | 119 min |
| Aug 12, 2:22 PM CDT | Mesoscale Discussion | SPC | Bond, Cass, Champaign, Christian, Clark, Clay and 26 more | 83 min |
| Aug 12, 5:19 PM CDT | Severe Thunderstorm Watch | SPC | Calhoun, Clinton, Greene, Jersey, Macoupin, Madison and 7 more | 5 hr |
| Aug 12, 3:30 PM CDT | Mesoscale Discussion | SPC | Audrain, Boone, Caldwell, Callaway, Carroll, Cass and 22 more | 90 min |
Nearby
Mesoscale Discussions in Missouri, 2021Mesoscale Discussions in Illinois, 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.