Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1703
The Storm Prediction Center issued this mesoscale discussion at Sep 7, 2021, 12:25 PM CDT for 15 counties in Illinois. It was in force for 65 min.
The area
The outline as issued.
The facts
- Issued
- Sep 7, 2021, 12:25 PM CDT (17:25 UTC)
- Expired
- Sep 7, 2021, 1:30 PM CDT
- In force
- 65 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Boone County, IL, Bureau County, IL, Carroll County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Kane County, IL, Kendall County, IL, Lake County, IL, Lee County, IL, McHenry County, IL, Ogle County, IL, Stephenson County, IL, Whiteside County, IL, Winnebago County, IL
The radar
The Chicago radar (KLOT), 78 km from the middle of the area, began a volume at 17:25 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, 5.4 hours before the alert went out and 140 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
- 827 J/kg
- Mixed-layer CIN
- -263 J/kg
- Mixed-layer LCL
- 1475 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km storm-relative helicity
- 185 m²/s²
- 0-3 km storm-relative helicity
- 167 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.1
The text
As transmitted.
906
ACUS11 KWNS 071726
SWOMCD
SPC MCD 071725
INZ000-ILZ000-WIZ000-IAZ000-071830-
Mesoscale Discussion 1703
NWS Storm Prediction Center Norman OK
1225 PM CDT Tue Sep 07 2021
Areas affected...Northern Illinois
Concerning...Severe potential...Watch possible
Valid 071725Z - 071830Z
Probability of Watch Issuance...40 percent
SUMMARY...The need for a watch in parts of northern Illinois is
uncertain. The most probable scenario is that stronger storms will
develop later this afternoon along the advancing front after
inhibition weakens further. Trends, however, will be monitored.
DISCUSSION...Storm motion with the ongoing convection in southern
Wisconsin is expected to keep that activity near and perhaps just
south into Illinois. Weak convection has developed in far northwest
Illinois along a pre-frontal boundary. So far this new convection
has struggled. Morning observed soundings from DVN and ILX showed
low-level dry air that is likely contributing to MLCIN. It seems
most likely that a few more hours of heating and moistening will be
needed, along with greater low-level forcing along the front, for
more substantial development to occur. That being said, model
guidance has been poor with timing and evolution of convection this
morning. A watch is not expected in the short term, but trends will
continue to be monitored in northern Illinois.
..Wendt/Hart.. 09/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...MKX...DVN...
LAT...LON 41309005 41609019 42069018 42278991 42378975 42528922
42518820 42498775 42528752 42308723 41598728 41558760
41348945 41309005SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 7, 1:12 PM CDT | Severe Thunderstorm Watch | SPC | Boone, Bureau, Champaign, Cook, DeKalb, DeWitt and 34 more | 8 hr |
| Sep 7, 3:14 PM CDT | Mesoscale Discussion | SPC | DuPage, Ford, Grundy, Iroquois, Kankakee, Kendall and 11 more | 91 min |
| 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.