Alert archive / Illinois / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 133, NWS Chicago, IL

July 21, 2017Cook County, DuPage County, Kane County, Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Jul 21, 2017, 4:14 PM CDT for Cook County, DuPage County, Kane County, Illinois. It was in force for 46 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, 4:14 PM CDT (21:14 UTC)
Expired
Jul 21, 2017, 5:00 PM CDT
In force
46 min
Issued by
NWS Chicago, IL
Area
Storm-based polygon
Hail
1.0 in
Wind
60.0 mph

Counties Cook County, IL, DuPage County, IL, Kane County, IL

The radar

The Chicago radar (KLOT), 32 km from the middle of the area, began a volume at 21:14 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, 9.2 hours before the alert went out and 199 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-pSkew-T log-p diagram, Lincoln, IL at 12:00Z on 2017-07-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1643 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Lincoln, IL at 12:00Z on 2017-07-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -31 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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, 2:56 PM CDT, 1 hour 18 minutes earlier.

Area forecast discussion, Jul 21, 2:56 PM CDT, 1 hour 18 minutes before
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Hazardous weather outlook, Jul 21, 12:49 PM CDT, 3 hours 25 minutes before
Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
1249 PM CDT Fri Jul 21 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
221800-
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-
1249 PM CDT Fri Jul 21 2017 /149 PM EDT Fri Jul 21 2017/

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

.DAY ONE...This Afternoon and Tonight.

WEATHER HAZARDS EXPECTED:
  Significant Thunderstorm Risk...with an associated:
      Significant Thunderstorm Wind Damage Risk...up to 70 mph.
      Elevated Hail Risk...up to quarter size.
      Limited Tornado Risk.
  Significant Flooding Risk.
  Significant Excessive Heat Risk this afternoon.

DISCUSSION:

Thunderstorm potential will increase late this afternoon through
early Saturday morning, with the potential to produce torrential rainfall
and flash flooding. Strong to severe storms will be most likely
from late this afternoon through this evening, with damaging winds
the primary severe weather threat, in addition to very heavy rainfall.
Behind the initial line of storms, additional heavy rain producing
thunderstorms will likely develop for some areas.
Heaviest rainfall amounts, in excess of 1.5 inches or more, are expected to
occur primarily over far northern Illinois north of Interstate 80.

Heat index readings will approach 105 degrees both today and
Saturday, mainly along and south of Interstate 80.

.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 Fox and
Des Plaines Rivers.

.SPOTTER INFORMATION STATEMENT...

Spotters will likely be needed beginning this evening.

GENERAL STORM MOTION OF THE DAY:

Toward the east-southeast at 35 to 40 mph.

&&

LMZ740>745-221800-
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-
1249 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...This Afternoon and Tonight.

  Significant Thunderstorm Risk.

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

Saturday and Sunday...
  Limited Thunderstorm Risk.
Monday...
  Hazardous Conditions for Small Craft are likely.
Thursday...
  Limited Thunderstorm Risk.

&&

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-221800-
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-
1249 PM CDT Fri Jul 21 2017

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

.DAY ONE...This Afternoon and Tonight.

Thunderstorms are likely across the southern half of the lake
this evening and overnight. Winds in excess of 30 kt are probable
this evening for this same area.

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

Low chances of thunderstorms exist for the weekend.

&&

KMD

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In the hours before

Local storm report, Jul 21, 12:32 PM CDT, 3 hours 42 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 4 minutes before
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Local storm report, Jul 21, 3:16 PM CDT, 58 minutes before
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Local storm report, Jul 21, 3:28 PM CDT, 46 minutes before
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Local storm report, Jul 21, 3:33 PM CDT, 41 minutes before
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The office that day

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

IssuedProductOfficeCountiesLasted
Jul 21, 12:30 AM CDTSpecial Weather StatementLOTLee30 min
Jul 21, 12:32 AM CDTSevere Thunderstorm WarningLOTDeKalb, LaSalle, Lee43 min
Jul 21, 12:57 AM CDTSevere Thunderstorm WarningLOTDeKalb, LaSalle14 min
Jul 21, 8:39 AM CDTRiver Flood AdvisoryLOTLaSalle5 days
Jul 21, 9:55 AM CDTRiver Flood WarningLOTWinnebago10 days
Jul 21, 9:55 AM CDTRiver Flood WarningLOTWinnebago11 days
Jul 21, 9:55 AM CDTRiver Flood WarningLOTOgle9 days
Jul 21, 2:39 PM CDTSevere Thunderstorm WarningLOTBoone, Winnebago36 min
Jul 21, 3:08 PM CDTSevere Thunderstorm WarningLOTBoone, DeKalb, McHenry37 min
Jul 21, 4:10 PM CDTRiver Flood AdvisoryLOTCook51 hr
Jul 21, 4:41 PM CDTRiver Flood WarningLOTCook3 days
Jul 21, 4:41 PM CDTSevere Thunderstorm WarningLOTCook, DuPage49 min
Jul 21, 4:53 PM CDTRiver Flood WarningLOTLaSalle5 days
Jul 21, 5:00 PM CDTRiver Flood AdvisoryLOTWill51 hr
Jul 21, 5:00 PM CDTRiver Flood AdvisoryLOTWill66 hr
Jul 21, 5:00 PM CDTRiver Flood AdvisoryLOTDuPage40 hr
Jul 21, 5:06 PM CDTSpecial Marine WarningLOT84 min
Jul 21, 5:09 PM CDTRiver Flood WarningLOTBoone4 days
Jul 21, 5:18 PM CDTAreal Flood AdvisoryLOTCook, DuPage, Kane3 hr
Jul 21, 5:22 PM CDTRiver Flood WarningLOTLee5 days
Jul 21, 6:30 PM CDTSevere Thunderstorm WarningLOTOgle45 min
Jul 21, 6:39 PM CDTSevere Thunderstorm WarningLOTGrundy, Kankakee, Livingston, Will51 min
Jul 21, 2:34 AM CDTSpecial Weather StatementLOTBenton, Jasper, Newton41 min

Nearby

Severe Thunderstorm Warnings in Illinois, 2017Every 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.