Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1707
The Storm Prediction Center issued this mesoscale discussion at Sep 7, 2021, 3:14 PM CDT for 17 counties in Illinois. It was in force for 91 min.
The area
The outline as issued.
The facts
- Issued
- Sep 7, 2021, 3:14 PM CDT (20:14 UTC)
- Expired
- Sep 7, 2021, 4:45 PM CDT
- In force
- 91 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 489
Counties DuPage County, IL, Ford 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, McLean County, IL, Peoria County, IL, Putnam County, IL, Stark County, IL, Tazewell County, IL, Will County, IL, Woodford County, IL
The radar
The Chicago radar (KLOT), 100 km from the middle of the area, began a volume at 20:18 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, 8.2 hours before the alert went out and 100 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1964 m above ground
- 0-6 km bulk shear
- 25 kt
- 0-1 km storm-relative helicity
- 93 m²/s²
- 0-3 km storm-relative helicity
- 115 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
527
ACUS11 KWNS 072014
SWOMCD
SPC MCD 072014
INZ000-ILZ000-072145-
Mesoscale Discussion 1707
NWS Storm Prediction Center Norman OK
0314 PM CDT Tue Sep 07 2021
Areas affected...Central Illinois
Concerning...Severe Thunderstorm Watch 489...
Valid 072014Z - 072145Z
The severe weather threat for Severe Thunderstorm Watch 489
continues.
SUMMARY...Damaging winds remain a threat, particularly with a
cluster moving towards the south side of Chicago. Isolated large
hail may also occur.
DISCUSSION...A cluster of intense storms responsible for several
large hail reports in northern Illinois continues to move
southeastward. Over the past 30 minutes this cluster has shown a
greater forward surge on KLOT radar imagery and has had recent
reports of severe winds and wind damage. This would indicate a
greater threat for damaging wind gusts as it moves near and south of
the Chicago suburbs and near Kankakee. Isolated large hail remains
possible even with a less favorable storm mode given cold
temperatures aloft and around 40 kts of effective shear. Though dry
air at low-levels has allowed some capping to remain, ascent in the
immediate frontal zone along with modest height falls this evening
should allow some continued activity into early evening. Additional
storm development into parts of west-central Illinois is less
certain as surface convergence is weaker as is the mid-level ascent.
..Wendt.. 09/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...ILX...DVN...
LAT...LON 41079024 41868840 41898803 41548746 40928745 40478814
40228956 40338988 40699032 41079024SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 7, 12:25 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 9 more | 65 min |
| Sep 7, 1:12 PM CDT | Severe Thunderstorm Watch | SPC | Boone, Bureau, Champaign, Cook, DeKalb, DeWitt and 34 more | 8 hr |
| Sep 7, 5:25 PM CDT | Mesoscale Discussion | SPC | Champaign, Vermilion | 95 min |
Nearby
Mesoscale 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.