Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1594
The Storm Prediction Center issued this mesoscale discussion at Aug 24, 2021, 3:09 PM CDT for 5 counties in Illinois; Green County, Rock County, Walworth County, Wisconsin. It was in force for 66 min.
The area
The outline as issued.
The facts
- Issued
- Aug 24, 2021, 3:09 PM CDT (20:09 UTC)
- Expired
- Aug 24, 2021, 4:15 PM CDT
- In force
- 66 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Boone County, IL, McHenry County, IL, Ogle County, IL, Stephenson County, IL, Winnebago County, IL, Green County, WI, Rock County, WI, Walworth County, WI
The radar
The Milwaukee radar (KMKX), 65 km from the middle of the area, began a volume at 20:11 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
Davenport, (KDVN), launched 12:00Z, 8.2 hours before the alert went out and 154 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
- 1809 J/kg
- Mixed-layer CIN
- -127 J/kg
- Mixed-layer LCL
- 1284 m above ground
- 0-6 km bulk shear
- 15 kt
- 0-1 km storm-relative helicity
- 35 m²/s²
- 0-3 km storm-relative helicity
- 9 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
351
ACUS11 KWNS 242009
SWOMCD
SPC MCD 242009
ILZ000-WIZ000-242115-
Mesoscale Discussion 1594
NWS Storm Prediction Center Norman OK
0309 PM CDT Tue Aug 24 2021
Areas affected...southeast Wisconsin through northeast Illinois
Concerning...Severe potential...Watch possible
Valid 242009Z - 242115Z
Probability of Watch Issuance...40 percent
SUMMARY...Organized MCS with a threat for damaging wind may continue
beyond WW 461 into southeast Wisconsin and northeast Illinois.
Trends are being monitored for a possible severe thunderstorm watch
by 21-22Z.
DISCUSSION...An organized MCS with embedded bowing segments and an
occasional rear inflow notch continues through northeast IA at
around 35 kt. The storms are developing along and north of an
outflow boundary that is moving slowly south and continues to
decelerate. The warm sector is very moist and unstable with 3500
J/kg MLCAPE. Storms will continue to ingest higher theta-e air that
is advecting northward above the shallow near-surface stable layer.
Farther downstream, a few thunderstorms are developing along the
boundary across southeast WI. These may serve to reinforce the
boundary and increase potential for storm interactions as the MCS
continues east.
..Dial/Kerr.. 08/24/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...MKX...DVN...
LAT...LON 42838986 43008879 42788794 42028794 41948947 42318974
42838986SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 24, 6:00 AM CDT | Mesoscale Discussion | SPC | Jo Daviess | 90 min |
| Aug 24, 1:52 PM CDT | Severe Thunderstorm Watch | SPC | Carroll, Jo Daviess, Rock Island, Stephenson, Whiteside | 5 hr |
| Aug 24, 3:55 PM CDT | Severe Thunderstorm Watch | SPC | Boone, Cook, DeKalb, DuPage, Kane, Lake and 4 more | 5 hr |
| Aug 24, 5:10 PM CDT | Mesoscale Discussion | SPC | Boone, Carroll, DeKalb, DuPage, Jo Daviess, Kane and 7 more | 2 hr |
| Aug 24, 2:17 AM CDT | Severe Thunderstorm Watch | SPC | Pierce, Polk, Saint Croix | 7 hr |
| Aug 24, 3:00 AM CDT | Mesoscale Discussion | SPC | Pierce, Polk, Saint Croix | 2 hr |
| Aug 24, 7:10 AM CDT | Mesoscale Discussion | SPC | Adams, Barron, Buffalo, Chippewa, Clark, Dunn and 15 more | 95 min |
| Aug 24, 9:13 AM CDT | Mesoscale Discussion | SPC | Brown, Calumet, Menominee, Oconto, Outagamie, Shawano and 3 more | 62 min |
| Aug 24, 12:44 PM CDT | Mesoscale Discussion | SPC | Crawford, Grant, Iowa, Richland, Sauk, Vernon | 91 min |
Nearby
Mesoscale Discussions in Illinois, 2021Mesoscale Discussions in Wisconsin, 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.