Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1495
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 3:16 AM CDT for 22 counties in Illinois; 10 counties in Indiana. It was in force for 119 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 3:16 AM CDT (08:16 UTC)
- Expired
- Aug 12, 2021, 5:15 AM CDT
- In force
- 119 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 32 counties
Bureau County, IL, Ford County, IL, Fulton County, IL, Grundy County, IL, Iroquois County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, LaSalle County, IL, Livingston County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, McLean County, IL, Peoria County, IL, Putnam County, IL, Schuyler County, IL, Stark County, IL, Tazewell County, IL, Warren County, IL, Will County, IL, Woodford County, IL, Jasper County, IN, Lake County, IN, LaPorte County, IN, Marshall County, IN, Newton County, IN, Porter County, IN, Pulaski County, IN, Saint Joseph County, IN, Starke County, IN, White County, IN
The radar
The Chicago radar (KLOT), 72 km from the middle of the area, began a volume at 08:16 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 00:00Z, 8.3 hours before the alert went out and 112 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
- 3800 J/kg
- Mixed-layer CIN
- -58 J/kg
- Mixed-layer LCL
- 1058 m above ground
- 0-6 km bulk shear
- 19 kt
- 0-1 km storm-relative helicity
- 255 m²/s²
- 0-3 km storm-relative helicity
- 406 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 20.7
The text
As transmitted.
661
ACUS11 KWNS 120817
SWOMCD
SPC MCD 120816
INZ000-MIZ000-ILZ000-121015-
Mesoscale Discussion 1495
NWS Storm Prediction Center Norman OK
0316 AM CDT Thu Aug 12 2021
Areas affected...Central IL...Northwest IN
Concerning...Severe potential...Watch unlikely
Valid 120816Z - 121015Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated damaging wind gusts and/or hail may occur across
central IL and northwest IN over the next hour or two.
DISCUSSION...Elevated thunderstorms continued to develop along and
ahead of the cold front pushing slowly southeastward across northern
IL. A predominantly multicellular mode has been observed over the
past hour or so, with occasional development of downdrafts strong
enough to penetrate the low-level stability and produce gusts at the
surface. Updrafts have been generally transient, likely a result of
only modest vertical shear.
The trends observed over the past hour will likely persist, with
strong buoyancy supporting occasionally robust updrafts amid a
generally disorganized storm mode. Given the ample low-level
moisture, a few wet downbursts may be strong enough to reach the
surface and produce damaging wind gusts. Storm mergers may also
result in updrafts strong enough for hail, although the warm
thermodynamic profiles may the hail threat less likely. Overall,
isolated severe thunderstorms are possible within the extended
portion of Severe Thunderstorm Watch 430, but an additional watch is
not anticipated.
..Mosier/Edwards.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IWX...LOT...ILX...DVN...
LAT...LON 41109093 41638876 41838719 41578589 40798659 40079062
41109093SPC 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, 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, 6:06 PM CDT | Mesoscale Discussion | SPC | Calhoun, Jersey, Madison, Monroe, Saint Clair | 84 min |
Nearby
Mesoscale Discussions in Illinois, 2021Mesoscale Discussions in Indiana, 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.