Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1508
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 9:55 PM CDT for 5 states. It was in force for 95 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 9:55 PM CDT (02:55 UTC)
- Expired
- Aug 12, 2021, 11:30 PM CDT
- In force
- 95 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 435
All 33 counties
Clay County, AR, Randolph County, AR, Alexander County, IL, Franklin County, IL, Gallatin County, IL, Hamilton County, IL, Hardin County, IL, Johnson County, IL, Massac County, IL, Pope County, IL, Pulaski County, IL, Saline County, IL, Union County, IL, White County, IL, Williamson County, IL, Ballard County, KY, Carlisle County, KY, Fulton County, KY, Hickman County, KY, Livingston County, KY, McCracken County, KY, Union County, KY, Bollinger County, MO, Butler County, MO, Cape Girardeau County, MO, Carter County, MO, Mississippi County, MO, New Madrid County, MO, Ripley County, MO, Scott County, MO, Stoddard County, MO, Wayne County, MO, Lake County, TN
The radar
The Paducah radar (KPAH), 50 km from the middle of the area, began a volume at 02:58 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
Nashville Metro, TN (KBNA), launched 00:00Z, 2.9 hours before the alert went out and 270 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.
253
ACUS11 KWNS 130256
SWOMCD
SPC MCD 130255
KYZ000-INZ000-ILZ000-TNZ000-MOZ000-ARZ000-130430-
Mesoscale Discussion 1508
NWS Storm Prediction Center Norman OK
0955 PM CDT Thu Aug 12 2021
Areas affected...Southeast MO...Northeast AR...Southern IL...Western
KY
Concerning...Severe Thunderstorm Watch 435...
Valid 130255Z - 130430Z
The severe weather threat for Severe Thunderstorm Watch 435
continues.
SUMMARY...A localized damaging wind threat will continue tonight,
though a gradual weakening trend is expected with time.
DISCUSSION...The convective line that earlier produced measured
severe wind gusts and wind damage around St. Louis has shown some
signs of weakening over the last hour across southern IL, with
warming cloud tops and weaker inbound winds from the KPAH radar
compared to what was observed earlier from the KLSX radar. The
gradual weakening trend is expected to continue as the boundary
layer cools and stabilizes, but as a substantial cold pool continues
to push southeastward in conjunction with this line, a localized
damaging wind threat will continue downstream as long as convection
remains active near the gust front.
Further southwest, convection has recently increased in intensity
across southeast MO, where somewhat greater buoyancy is in place per
recent mesoanalyses. While this area is removed from the stronger
cold pool surge to the east, a localized damaging wind risk may also
materialize into far southeast MO and northeast AR into the late
evening hours.
..Dean.. 08/13/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PAH...MEG...LSX...LZK...SGF...
LAT...LON 37088838 36228955 36339108 36759142 37269067 37398979
37858918 38398853 38238797 37918788 37548795 37088838SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 13, 12:24 PM CDT | Mesoscale Discussion | SPC | Cleburne, Conway, Craighead, Crawford, Crittenden, Cross and 23 more | 2 hr |
| Aug 12, 7:20 PM CDT | Mesoscale Discussion | SPC | Alexander, Franklin, Gallatin, Hamilton, Hardin, Jackson and 11 more | 85 min |
| Aug 12, 7:37 PM CDT | Severe Thunderstorm Watch | SPC | Alexander, Franklin, Gallatin, Hamilton, Hardin, Jackson and 10 more | 4 hr |
| 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.