Alert archive / Illinois / Flash Flood Warnings in 2020

Flash Flood Warning 6, NWS Chicago, IL

May 17, 202013 counties in Illinois

NWS Chicago, IL issued this flash flood warning at May 17, 2020, 4:32 PM CDT for 13 counties in Illinois. It was in force for 6 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: May 17, 2020, 4:32 PM CDT (21:32 UTC)
Expired: May 17, 2020, 10:30 PM CDT
In force: 6 hr
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Flood severity: None

Counties Cook County, IL, DuPage County, IL, Ford County, IL, Grundy County, IL, Iroquois County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Lake County, IL, LaSalle County, IL, Livingston County, IL, McHenry County, IL, Will County, IL

The radar

The Chicago radar (KLOT), 16 km from the middle of the area, began a volume at 21:36 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, 9.5 hours before the alert went out and 153 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: 40 J/kg
Mixed-layer CIN: -26 J/kg
Mixed-layer LCL: 599 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 167 m²/s²
0-3 km storm-relative helicity: 173 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 May 17, 2:30 PM CDT, 2 hours 2 minutes earlier.

Area forecast discussion, May 17, 2:30 PM CDT, 2 hours 2 minutes before

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Hazardous weather outlook, May 17, 3:35 PM CDT, 57 minutes before

Hazardous Weather Outlook...CORRECTED
National Weather Service Chicago/Romeoville IL
335 PM CDT Sun May 17 2020

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-182015-
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-
335 PM CDT Sun May 17 2020 /435 PM EDT Sun May 17 2020/

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

.DAY ONE...Tonight.

Weather hazards expected...

  Significant Flooding Risk.
  Significant Thunderstorm Risk...with an associated:
     Elevated Tornado risk mainly south of I-80.
     Limited damaging wind risk...up to 60 mph.
  Elevated Fog Risk.
  Elevated Lakeshore Flood Risk Illinois shore.

DISCUSSION...

Showers and storms will increase and coverage and intensity
through this afternoon. The ground is saturated and anticipated
swaths of heavy rainfall are therefore expected to result in flash
flooding, some potentially significant, along with renewed river
rises. A threat for severe storms exists this afternoon and
evening, with a potential for damaging wind gusts and and even a
few tornadoes, mainly south of I-80 and east of I-39.

Some dense fog will be possible tonight. In addition, increasing
surge and waves will result in a threat for minor lakeshore
flooding across the Illinois shore.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Monday and Tuesday...
  Elevated Fog Risk.
  Elevated Lakeshore Flood Risk.
Thursday through Saturday...
  Limited Thunderstorm Risk.

DISCUSSION:

Near record water levels combined with gusty northeast winds,
increased wave action, and developing surge may lead to areas of
lakeshore flooding Monday into Tuesday.

.SPOTTER INFORMATION STATEMENT...

  Spotters may be needed this afternoon and evening.

GENERAL STORM MOTION OF THE DAY:

  Individual storms moving toward the northeast at 30 to 35 mph,
  with the line of storms motion generally toward the east at
  10 to 15 mph.

LMZ740>745-182015-
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-
335 PM CDT Sun May 17 2020

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...

  Hazardous conditions for small craft.
  Elevated Thunderstorm Risk...with an associated:
     Limited thunderstorm wind gust risk...up to 45 kts.
  Elevated Fog Risk.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Monday...
  Hazardous conditions for small craft are likely.
  Elevated Fog Risk.
Tuesday and Wednesday...
  Hazardous conditions for small craft are likely.
Friday and Saturday...
  Limited Thunderstorm Risk.

Carlaw

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In the hours before

Special weather statement, May 17, 1:48 PM CDT, 2 hours 44 minutes before

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Local storm report, May 17, 2:40 PM CDT, 1 hour 52 minutes before

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Local storm report, May 17, 3:54 PM CDT, 38 minutes before

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Local storm report, May 17, 4:00 PM CDT, 32 minutes before

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Local storm report, May 17, 4:26 PM CDT, 6 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
May 16, 7:21 PM CDT	River Flood Watch	LOT		45 hr
May 16, 7:26 PM CDT	River Flood Advisory	LOT	DeKalb	48 hr
May 16, 7:48 PM CDT	River Flood Advisory	LOT	Cook	68 hr
May 16, 7:51 PM CDT	River Flood Advisory	LOT	Iroquois	17 hr
May 16, 7:52 PM CDT	River Flood Warning	LOT	LaSalle	5 days
May 16, 8:00 PM CDT	River Flood Watch	LOT	Grundy	17 hr
May 16, 8:09 PM CDT	River Flood Warning	LOT	Lake	7 days
May 16, 8:20 PM CDT	River Flood Warning	LOT	Cook	6 days
May 16, 9:16 PM CDT	Small Craft Advisory	LOT		3 days
May 17, 5:43 AM CDT	River Flood Warning	LOT	Cook	4 days
May 17, 12:42 PM CDT	River Flood Warning	LOT	Iroquois	5 days
May 17, 12:44 PM CDT	River Flood Warning	LOT	Boone	4 days
May 17, 12:44 PM CDT	River Flood Warning	LOT	Ogle	45 hr
May 17, 12:49 PM CDT	River Flood Warning	LOT	Grundy, Kankakee, Will	7 days
May 17, 1:12 PM CDT	River Flood Advisory	LOT	Winnebago	25 hr
May 17, 1:12 PM CDT	River Flood Advisory	LOT	Winnebago	33 hr
May 17, 1:15 PM CDT	River Flood Watch	LOT	Iroquois	6 days
May 17, 1:15 PM CDT	River Flood Watch	LOT	Iroquois, Kankakee	5 days
May 17, 1:48 PM CDT	Special Weather Statement	LOT	Livingston	27 min
May 17, 2:04 PM CDT	Areal Flood Advisory	LOT	Boone, DeKalb, Kane, Kendall, Lake, LaSalle and 3 more	6 hr
May 17, 2:14 PM CDT	Areal Flood Advisory	LOT	Cook, DuPage, Ford, Grundy, Iroquois, Kankakee and 4 more	3 hr
May 17, 2:54 PM CDT	Marine Dense Fog Advisory	LOT		52 hr
May 17, 3:29 PM CDT	Areal Flood Advisory	LOT	Cook, DuPage, Grundy, Kane, Kendall, Lake and 3 more	94 min
May 17, 5:43 PM CDT	Areal Flood Advisory	LOT	Ford, Iroquois, Kankakee	3 hr
May 17, 6:48 PM CDT	Flash Flood Warning Considerable damage threat	LOT	Cook, DuPage, Kankakee, Lake, Will	3 hr
May 17, 6:59 PM CDT	Special Marine Warning	LOT		31 min
May 16, 7:32 PM CDT	River Flood Warning	LOT	Lake	65 hr
May 16, 8:07 PM CDT	River Flood Advisory	LOT	Newton	6 days
May 17, 1:07 PM CDT	River Flood Watch	LOT	Porter	21 days
May 17, 1:07 PM CDT	River Flood Watch	LOT	Jasper, Porter	21 days
May 17, 1:07 PM CDT	River Flood Watch	LOT	Jasper	4 days

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.