Alert archive / Illinois / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 134, NWS Chicago, IL

July 21, 2017Cook County, DuPage County, Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Jul 21, 2017, 4:41 PM CDT for Cook County, DuPage County, Illinois. It was in force for 49 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Jul 21, 2017, 4:41 PM CDT (21:41 UTC)
Expired: Jul 21, 2017, 5:30 PM CDT
In force: 49 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Hail: 1.25 in
Wind: 60.0 mph

Counties Cook County, IL, DuPage County, IL

The radar

The Chicago radar (KLOT), 35 km from the middle of the area, began a volume at 21:41 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, 9.7 hours before the alert went out and 201 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: 1643 J/kg
Mixed-layer CIN: -136 J/kg
Mixed-layer LCL: 949 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: -31 m²/s²
0-3 km storm-relative helicity: 36 m²/s²
Significant tornado parameter: -0.1
Supercell composite: -0.9

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning 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 severe thunderstorm warning went out at Jul 21, 4:31 PM CDT, 10 minutes earlier.

Area forecast discussion, Jul 21, 4:31 PM CDT, 10 minutes before

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Hazardous weather outlook, Jul 21, 4:21 PM CDT, 20 minutes before

Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
421 PM CDT Fri Jul 21 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
222130-
Winnebago-Boone-McHenry-Lake Illinois-Ogle-Lee-De Kalb-Kane-
DuPage-Cook-La Salle-Kendall-Grundy-Will-Kankakee-Livingston-
Iroquois-Ford-Lake Indiana-Porter-Newton-Jasper-Benton-
421 PM CDT Fri Jul 21 2017 /521 PM EDT Fri Jul 21 2017/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS...
NORTHEAST ILLINOIS AND NORTHWEST INDIANA.

.DAY ONE...Tonight.

WEATHER HAZARDS EXPECTED:
  Significant Thunderstorm Risk...with an associated:
      Elevated Tornado Risk Along and West of I-39.
      Elevated Hail Risk...up to quarter size.
      Significant Thunderstorm Wind Damage Risk...up to 70
MPH.
  Significant Flooding Risk.
  Significant Excessive Heat Risk.

DISCUSSION:

Severe thunderstorms expected early this evening through late
evening across the entire outlook area, with damaging winds the
primary severe weather threat. In addition, there is an isolated
tornado threat, mainly along and west of I-39. Also, torrential
rainfall will be possible with any storm. Behind the initial
complex of storms, additional heavy rain producing thunderstorms
will likely develop overnight, especially across northern
Illinois. Heaviest rainfall amounts, of 1 to 3 inches or more,
are expected to occur primarily over northern Illinois north of
Interstate 80.

In addition, flooding will continue along portions of the Des
Plaines, Fox, and Kishwaukee rivers.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday...
  Limited Flooding Risk.
  Elevated Severe Thunderstorm Risk.
  Elevated Excessive Heat Risk.
Sunday...
  Limited Severe Thunderstorm Risk.
Thursday...
  Limited Thunderstorm Risk.

In addition, flooding will continue along portions of the Des
Plaines, Fox, Kishwaukee, Rock, and Pecatonica rivers.

.SPOTTER INFORMATION STATEMENT...

Spotters will likely be needed early this evening and overnight.

GENERAL STORM MOTION OF THE DAY:

Toward the east-southeast at 30 to 40 mph.

&&

LMZ740>745-222130-
Winthrop Harbor to Wilmette Harbor-
Wilmette Harbor to Northerly Island-
Northerly Island to Calumet Harbor-Calumet Harbor to Gary-
Gary to Burns Harbor-Burns Harbor to Michigan City-
421 PM CDT Fri Jul 21 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS NEARSHORE
WATERS OF LAKE MICHIGAN AND THE INDIANA NEARSHORE WATERS OF LAKE
MICHIGAN.

.DAY ONE...Tonight.

  Significant Thunderstorm Risk.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday and Sunday...
  Limited Thunderstorm Risk.
Thursday...
  Limited Thunderstorm Risk.

&&

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-222130-
Lake Michigan from Michigan City IN to St. Joseph MI 5 NM
offshore to Mid Lake-
Lake Michigan from Seul Choix Point to Rock Island Passage 5 NM
offshore to Mid Lake-
Lake Michigan South of a line from Seul Choix Point to the
Mackinac Bridge and north of a line from Charlevoix MI to South
Fox Island 5 NM offshore-
Lake Michigan from Charlevoix to Point Betsie MI 5 NM offshore to
Mid Lake-
Lake Michigan from Point Betsie to Manistee MI 5 NM offshore to
Mid Lake-
Lake Michigan from Rock Island Passage to Sturgeon Bay WI-
Lake Michigan from Sturgeon Bay to Two Rivers WI 5 NM offshore to
Mid Lake-
Lake Michigan from Two Rivers to Sheboygan WI 5 NM offshore to
Mid Lake-
Lake Michigan from Sheboygan to Port Washington WI 5 NM offshore
to Mid Lake-
Lake Michigan from Port Washington to North Point Light WI 5 NM
offshore to Mid Lake-
Lake Michigan from North Point Light to Wind Point WI 5 NM
offshore to Mid Lake-
Lake Michigan from Wind Point WI to Winthrop Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Winthrop Harbor to Wilmette Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Wilmette Harbor IL to Michigan City IN 5 NM
offshore to Mid Lake-
Lake Michigan from Pentwater to Manistee MI 5 NM offshore to Mid
Lake-
Lake Michigan from Whitehall to Pentwater MI 5 NM offshore to Mid
Lake-
Lake Michigan from Grand Haven to Whitehall MI 5 NM offshore to
Mid Lake-
Lake Michigan from Holland to Grand Haven MI 5 NM offshore to Mid
Lake-
Lake Michigan from South Haven to Holland MI 5 NM offshore to Mid
Lake-
Lake Michigan from St. Joseph to South Haven MI 5 NM offshore to
Mid Lake-
421 PM CDT Fri Jul 21 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE OPEN WATERS OF LAKE
MICHIGAN.

.DAY ONE...Tonight.

Thunderstorms are likely across the lake this evening and
overnight. Winds in excess of 30 kt are probable this evening,
mainly for the south half.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Low chances of thunderstorms exist for the weekend.

&&

Rodriguez

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In the hours before

Local storm report, Jul 21, 12:32 PM CDT, 4 hours 9 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1232 PM CDT FRI JUL 21 2017

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

0130 AM     TSTM WND DMG     5 SSW WILMINGTON        41.23N 88.20W
07/21/2017                   WILL               IL   TRAINED SPOTTER

            TREE BARANCHES DOWN AND AT LEAST ONE TREE UPROOTED. TIME
            ESTIMATED BY RADAR.

&&

MDB

Local storm report, Jul 21, 3:10 PM CDT, 1 hour 31 minutes before

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Local storm report, Jul 21, 3:16 PM CDT, 1 hour 25 minutes before

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Local storm report, Jul 21, 3:28 PM CDT, 1 hour 13 minutes before

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Local storm report, Jul 21, 3:33 PM CDT, 1 hour 8 minutes before

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Local storm report, Jul 21, 4:18 PM CDT, 23 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
Jul 21, 12:30 AM CDT	Special Weather Statement	LOT	Lee	30 min
Jul 21, 12:32 AM CDT	Severe Thunderstorm Warning	LOT	DeKalb, LaSalle, Lee	43 min
Jul 21, 12:57 AM CDT	Severe Thunderstorm Warning	LOT	DeKalb, LaSalle	14 min
Jul 21, 8:39 AM CDT	River Flood Advisory	LOT	LaSalle	5 days
Jul 21, 9:55 AM CDT	River Flood Warning	LOT	Winnebago	10 days
Jul 21, 9:55 AM CDT	River Flood Warning	LOT	Winnebago	11 days
Jul 21, 9:55 AM CDT	River Flood Warning	LOT	Ogle	9 days
Jul 21, 2:39 PM CDT	Severe Thunderstorm Warning	LOT	Boone, Winnebago	36 min
Jul 21, 3:08 PM CDT	Severe Thunderstorm Warning	LOT	Boone, DeKalb, McHenry	37 min
Jul 21, 4:10 PM CDT	River Flood Advisory	LOT	Cook	51 hr
Jul 21, 4:14 PM CDT	Severe Thunderstorm Warning	LOT	Cook, DuPage, Kane	46 min
Jul 21, 4:41 PM CDT	River Flood Warning	LOT	Cook	3 days
Jul 21, 4:53 PM CDT	River Flood Warning	LOT	LaSalle	5 days
Jul 21, 5:00 PM CDT	River Flood Advisory	LOT	Will	51 hr
Jul 21, 5:00 PM CDT	River Flood Advisory	LOT	Will	66 hr
Jul 21, 5:00 PM CDT	River Flood Advisory	LOT	DuPage	40 hr
Jul 21, 5:06 PM CDT	Special Marine Warning	LOT		84 min
Jul 21, 5:09 PM CDT	River Flood Warning	LOT	Boone	4 days
Jul 21, 5:18 PM CDT	Areal Flood Advisory	LOT	Cook, DuPage, Kane	3 hr
Jul 21, 5:22 PM CDT	River Flood Warning	LOT	Lee	5 days
Jul 21, 6:30 PM CDT	Severe Thunderstorm Warning	LOT	Ogle	45 min
Jul 21, 6:39 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, Kankakee, Livingston, Will	51 min
Jul 21, 2:34 AM CDT	Special Weather Statement	LOT	Benton, Jasper, Newton	41 min

Nearby

Severe Thunderstorm Warnings in Illinois, 2017 Every severe thunderstorm warning in 2017

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.