Alert archive / Illinois / Flash Flood Warnings in 2020

Flash Flood Warning 17, NWS Chicago, IL

June 29, 2020Boone County, McHenry County, Winnebago County, Illinois

NWS Chicago, IL issued this flash flood warning at Jun 29, 2020, 4:23 PM CDT for Boone County, McHenry County, Winnebago County, Illinois. It was in force for 4 hr. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Jun 29, 2020, 4:23 PM CDT (21:23 UTC)
Expired: Jun 29, 2020, 8:15 PM CDT
In force: 4 hr
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Flood severity: None

Counties Boone County, IL, McHenry County, IL, Winnebago County, IL

The radar

The Milwaukee radar (KMKX), 74 km from the middle of the area, began a volume at 21:23 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

Davenport, (KDVN), launched 12:00Z, 9.4 hours before the alert went out and 160 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: 1499 J/kg
Mixed-layer CIN: -120 J/kg
Mixed-layer LCL: 1072 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: 3 m²/s²
0-3 km storm-relative helicity: 12 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this flash flood 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 flash flood warning went out at Jun 29, 2:54 PM CDT, 1 hour 29 minutes earlier.

Area forecast discussion, Jun 29, 2:54 PM CDT, 1 hour 29 minutes before

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Hazardous weather outlook, Jun 29, 3:28 PM CDT, 55 minutes before

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In the hours before

Special weather statement, Jun 29, 1:20 PM CDT, 3 hours 3 minutes before

SPECIAL WEATHER STATEMENT
National Weather Service Chicago/Romeoville IL
120 PM CDT Mon Jun 29 2020

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-300000-
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-
Including the cities of Rockford, Belvidere, Crystal Lake,
Algonquin, McHenry, Woodstock, Waukegan, Buffalo Grove,
Mundelein, Gurnee, Rochelle, Oregon, Byron, Dixon, DeKalb,
Sycamore, Aurora, Elgin, Naperville, Wheaton, Downers Grove,
Lombard, Carol Stream, Ottawa, Streator, La Salle, Mendota,
Marseilles, Oswego, Yorkville, Plano, Morris, Coal City, Minooka,
Kankakee, Bourbonnais, Bradley, Pontiac, Dwight, Fairbury,
Watseka, Gilman, Paxton, Gibson City, Evanston, Des Plaines,
Schaumburg, Palatine, Northbrook, Chicago, Cicero, Oak Lawn,
Oak Park, La Grange, Calumet City, Oak Forest, Lemont,
Orland Park, Park Forest, Joliet, Bolingbrook, Plainfield,
Mokena, Channahon, Manhattan, Wilmington, Crete, Peotone,
Beecher, Gary, Hammond, Merrillville, Portage, Valparaiso,
Chesterton, Roselawn, Kentland, Morocco, Rensselaer, DeMotte,
Fowler, and Oxford
120 PM CDT Mon Jun 29 2020 /220 PM EDT Mon Jun 29 2020/

...SCATTERED THUNDERSTORMS TO CONTINUE THIS AFTERNOON...

Scattered thunderstorms will continue developing this afternoon
across northern Illinois. The thunderstorms will be capable of
producing frequent cloud to ground lightning, winds strong enough to
down small tree branches, small hail, and torrential downpours. Move
indoors until 30 minutes after the last rumble of thunder.

Isolated severe thunderstorms are possible, with winds strong enough
to bring down large tree branches, hail large enough to dent cars,
and rain rates heavy enough to cause flash flooding. If such a storm
is identified, a severe thunderstorm or flash flood warning will be
issued.  Make sure to have multiple ways to receive warnings.

Borchardt

Local storm report, Jun 29, 3:31 PM CDT, 52 minutes before

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Local storm report, Jun 29, 3:32 PM CDT, 51 minutes before

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Local storm report, Jun 29, 3:46 PM CDT, 37 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
Jun 28, 7:56 PM CDT	River Flood Advisory	LOT	Iroquois	25 hr
Jun 29, 3:20 PM CDT	Severe Thunderstorm Warning	LOT	Cook, Kane, Lake, McHenry	25 min
Jun 29, 3:33 PM CDT	Areal Flood Advisory	LOT	Boone, Cook, Kane, Lake, McHenry, Ogle and 1 more	3 hr
Jun 29, 4:11 PM CDT	Severe Thunderstorm Warning	LOT	Cook	64 min
Jun 29, 4:16 PM CDT	Special Marine Warning	LOT		89 min
Jun 29, 4:31 PM CDT	Areal Flood Advisory	LOT	Cook, Lake	119 min
Jun 29, 5:00 PM CDT	Areal Flood Advisory	LOT	DeKalb, Kane, Ogle	2 hr
Jun 29, 5:26 PM CDT	Areal Flood Advisory	LOT	Kankakee, Will	2 hr
Jun 29, 6:30 PM CDT	Areal Flood Advisory	LOT	Cook, DuPage, Kane, Lake, McHenry	2 hr
Jun 29, 4:35 PM CDT	Areal Flood Advisory	LOT	Lake	115 min
Jun 29, 5:41 PM CDT	Areal Flood Advisory	LOT	Lake, Porter	2 hr

Nearby

Flash Flood Warnings in Illinois, 2020 Every flash flood warning in 2020

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.