Alert archive / Illinois / Special Weather Statements in 2021

Special Weather Statement, NWS Chicago, IL

August 9, 2021Grundy County, Illinois

NWS Chicago, IL issued this special weather statement at Aug 9, 2021, 9:19 PM CDT for Grundy County, Illinois. It was in force for 26 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 9, 2021, 9:19 PM CDT (02:19 UTC)
Expired: Aug 9, 2021, 9:45 PM CDT
In force: 26 min
Issued by: NWS Chicago, IL
Hail: 0.00 in
Wind: 40

County Grundy County, IL

The radar

The Chicago radar (KLOT), 40 km from the middle of the area, began a volume at 02:20 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 00:00Z, 2.3 hours before the alert went out and 127 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 4598 J/kg
Mixed-layer CIN: -5 J/kg
Mixed-layer LCL: 775 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 179 m²/s²
0-3 km storm-relative helicity: 284 m²/s²
Significant tornado parameter: 3.9
Supercell composite: 24.2

Open this sounding in Storm Lab

The text

As transmitted.

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What forecasters said that day

The local office's own words before this special weather statement went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Chicago, IL wrote its last area forecast discussion before this special weather statement went out at Aug 9, 9:13 PM CDT, 6 minutes earlier.

Area forecast discussion, Aug 9, 9:13 PM CDT, 6 minutes before

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Hazardous weather outlook, Aug 9, 3:49 PM CDT, 5 hours 30 minutes before

Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
349 PM CDT Mon Aug 9 2021

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-102100-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
349 PM CDT Mon Aug 9 2021 /449 PM EDT Mon Aug 9 2021/

This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Elevated Thunderstorm Risk...with an associated:
     Limited Tornado risk.
     Limited hail risk...up to nickel size.
     Limited damaging wind risk...up to 70 mph.
  Limited Flooding Risk.
  Limited Excessive Heat Risk.

DISCUSSION...

Severe thunderstorms are possible across northern Illinois and
northwest Indiana this evening, with an
areawide threat for damaging winds, large hail, and a tornado or
two. The threat for locally heavy rainfall and flooding also
exists, especially in the late evening and overnight.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  Elevated Severe Thunderstorm Risk.
  Limited Flooding Risk.
  Elevated Excessive Heat Risk.
Wednesday...
  Limited Severe Thunderstorm Risk.
  Limited Excessive Heat Risk.
Thursday...
  Limited Thunderstorm Risk.
  Limited Excessive Heat Risk.
Friday...
  Limited Thunderstorm Risk.

DISCUSSION:

Periodic thunderstorms are expected through Friday, with strong
to severe storms possible Tuesday.

Warm and very humid conditions will persist through Thursday.
Heat indices over 100 are expected during the afternoon hours,
with dangerous heat index values likely surpassing 105 Tuesday
afternoon in many locations.

.SPOTTER INFORMATION STATEMENT...

  Spotters may be needed this evening.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east southeast around 25 mph.

LMZ740>745-102100-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
349 PM CDT Mon Aug 9 2021

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

Weather hazards expected...

  Elevated Thunderstorm Risk...with an associated:
     Limited Waterspout Risk.
     Limited hail risk...up to nickel size.
     Limited thunderstorm wind gust risk...up to 50 knots.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  Elevated Severe Thunderstorm Risk.
Wednesday...
  Limited Severe Thunderstorm Risk.
Thursday and Friday...
  Limited Thunderstorm Risk.

Lenning

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In the hours before

Local storm report, Aug 9, 7:04 PM CDT, 2 hours 15 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
704 PM CDT MON AUG 9 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0658 PM     TORNADO          1 WSW CAMPTON HILLS     41.93N 88.42W
08/09/2021                   KANE               IL   TRAINED SPOTTER

            MULTIPLE REPORTS OF A BRIEF TORNADO NEAR
            CAMPTON HILLS.

&&

WSL

Local storm report, Aug 9, 7:17 PM CDT, 2 hours 2 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
717 PM CDT MON AUG 9 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0405 PM     FLOOD            1 E ROCKFORD            42.27N 89.07W
08/09/2021                   WINNEBAGO          IL   PUBLIC

            MULTIPLE VIDEOS SHARED VIA SOCIAL MEDIA SHOW
            MINOR STREET FLOODING IN ROCKFORD.

&&

WSL

Local storm report, Aug 9, 7:23 PM CDT, 1 hour 56 minutes before

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Local storm report, Aug 9, 7:28 PM CDT, 1 hour 51 minutes before

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Local storm report, Aug 9, 7:51 PM CDT, 1 hour 28 minutes before

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Special weather statement, Aug 9, 9:19 PM CDT, 0 minutes before

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The office that day

Everything else NWS Chicago, IL issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 9, 7:18 PM CDT	Severe Thunderstorm Warning	LOT	Cook, DuPage	42 min
Aug 9, 8:21 PM CDT	Special Marine Warning	LOT		114 min
Aug 9, 9:30 PM CDT	Tornado Warning	LOT	Kankakee, Will	45 min
Aug 9, 10:06 PM CDT	Tornado Warning	LOT	Will	54 min
Aug 9, 10:12 PM CDT	Special Marine Warning	LOT		2 hr
Aug 10, 3:07 PM CDT	Heat Advisory	LOT	Boone, Cook, DeKalb, DuPage, Ford, Grundy and 12 more	28 hr
Aug 10, 5:21 PM CDT	Special Weather Statement	LOT	Lee, Ogle, Winnebago	54 min
Aug 10, 5:39 PM CDT	Severe Thunderstorm Warning	LOT	Lee, Ogle, Winnebago	81 min
Aug 10, 6:10 PM CDT	Severe Thunderstorm Warning	LOT	DeKalb, LaSalle, Lee	65 min
Aug 10, 6:16 PM CDT	Severe Thunderstorm Warning	LOT	Boone, DeKalb, McHenry	74 min
Aug 10, 6:34 PM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Cook, DuPage, Kane, Lake, McHenry	86 min
Aug 10, 6:38 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, Kane, Kendall	82 min
Aug 10, 6:55 PM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Cook, DuPage, Will	95 min

Nearby

Special Weather Statements in Illinois, 2021 Every special weather statement 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.