Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1641
The Storm Prediction Center issued this mesoscale discussion at Aug 29, 2021, 1:18 PM CDT for 26 counties in Illinois; Lake County, Newton County, Indiana; Kenosha County, Wisconsin. It was in force for 87 min.
The area
The outline as issued.
The facts
- Issued
- Aug 29, 2021, 1:18 PM CDT (18:18 UTC)
- Expired
- Aug 29, 2021, 2:45 PM CDT
- In force
- 87 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 29 counties
Bureau County, IL, Champaign County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Ford County, IL, Grundy County, IL, Henry County, IL, Iroquois County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Marshall County, IL, McHenry County, IL, McLean County, IL, Peoria County, IL, Putnam County, IL, Stark County, IL, Tazewell County, IL, Will County, IL, Woodford County, IL, Lake County, IN, Newton County, IN, Kenosha County, WI
The radar
The Chicago radar (KLOT), 59 km from the middle of the area, began a volume at 18:20 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, 6.3 hours before the alert went out and 124 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
- 810 J/kg
- Mixed-layer CIN
- -63 J/kg
- Mixed-layer LCL
- 1215 m above ground
- 0-6 km bulk shear
- 21 kt
- 0-1 km storm-relative helicity
- 63 m²/s²
- 0-3 km storm-relative helicity
- 91 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.8
The text
As transmitted.
590
ACUS11 KWNS 291818
SWOMCD
SPC MCD 291818
INZ000-ILZ000-WIZ000-291945-
Mesoscale Discussion 1641
NWS Storm Prediction Center Norman OK
0118 PM CDT Sun Aug 29 2021
Areas affected...Northern Illinois and far Northwestern Indiana
Concerning...Severe potential...Watch unlikely
Valid 291818Z - 291945Z
Probability of Watch Issuance...20 percent
SUMMARY...A few multicell storms capable of isolated damaging wind
gusts possible this afternoon.
DISCUSSION...Regional radar show a line of storms that have
initiated along a cold front across northern and northwestern
Illinois. Minimal cloud cover this morning has allowed the
downstream surface environment to warm rapidly into the mid 80s F
amid rich low-level moisture (dew point temperatures in the low 70s
F). This has allowed the atmosphere to destabilize, resulting in
MLCAPE values near 2000-2500 J/kg. Low-level winds are veered ahead
of the front and forecast soundings indicate predominately
unidirectional shear profiles. This area is situated along the
southern periphery of the advancing mid-level trough, and thus,
generally weak flow aloft is yielding little in the way of
deep-layer shear (effective bulk shear perhaps approaching 20 kt).
Nevertheless, continued heating through the afternoon may yield
low-level lapse rates near 7 C/km sufficient to aid in the threat
for localized damaging wind gusts with any multicell clusters that
are able to persist along the advancing front this afternoon.
..Karstens/Grams.. 08/29/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IND...LOT...ILX...MKX...DVN...
LAT...LON 40278979 41089065 42018914 42978811 42688760 41478713
40538741 40118799 40278979SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 29, 3:08 PM CDT | Mesoscale Discussion | SPC | Elkhart, Fulton, Jasper, Kosciusko, LaGrange, LaPorte and 9 more | 97 min |
Nearby
Mesoscale Discussions in Illinois, 2021Mesoscale Discussions in Indiana, 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.