Alert archive / Illinois / Flash Flood Warnings in 2021

Flash Flood Warning 10, NWS Chicago, IL

August 25, 20214 counties in Illinois

NWS Chicago, IL issued this flash flood warning at Aug 25, 2021, 9:06 PM CDT for 4 counties in Illinois. It was in force for 5 hr. 4 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Aug 25, 2021, 9:06 PM CDT (02:06 UTC)
Expired: Aug 26, 2021, 1:38 AM CDT
In force: 5 hr
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Flood severity: None

Counties DuPage County, IL, Kane County, IL, Kendall County, IL, Will County, IL

The radar

The Chicago radar (KLOT), 27 km from the middle of the area, began a volume at 02:08 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.

What was reported inside it

Time	Report	Where	Remark
Aug 25, 9:24 PM CDT	HEAVY RAIN 3.37	3 Nw Montgomery, IL	STATION ID KILAUROR108. ONE HOUR RAINFALL. HEAVY RAIN CONTINUES.
Aug 25, 9:25 PM CDT	HEAVY RAIN 3.14	3 E Sugar Grove, IL	STATION ID KILAUROR86. ONE HOUR RAINFALL.
Aug 25, 9:35 PM CDT	HEAVY RAIN 2.11	2 Wnw Crystal Lawns, IL	2.11 INCHES OF RAIN IN THE PAST 60 MINUTES.
Aug 25, 9:47 PM CDT	HEAVY RAIN 4.1	1 Nw Montgomery, IL	MESONET STATION ID KILAUROR112. RAINFALL SINCE 8:00 PM CDT.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Lincoln, IL (KILX), launched 00:00Z, 2.1 hours before the alert went out and 181 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: 2295 J/kg
Mixed-layer CIN: -13 J/kg
Mixed-layer LCL: 1479 m above ground
0-6 km bulk shear: 16 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 40 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

800 
WGUS53 KLOT 260206
FFWLOT
ILC043-089-093-197-260800-
/O.NEW.KLOT.FF.W.0010.210826T0206Z-210826T0800Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Chicago IL
906 PM CDT Wed Aug 25 2021

The National Weather Service in Chicago has issued a

* Flash Flood Warning for...
  Southwestern DuPage County in northeastern Illinois...
  Southern Kane County in northeastern Illinois...
  Northeastern Kendall County in northeastern Illinois...
  Northwestern Will County in northeastern Illinois...

* Until 300 AM CDT.

* At 906 PM CDT, doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between up to 2 inches of rain 
  have fallen. Additional rainfall amounts of 1 to 3 inches are 
  possible in the warned area. Flash flooding is ongoing or expected 
  to begin shortly.

  HAZARD...Flash flooding.

  SOURCE...Radar.

  IMPACT...Rapid-onset flooding of small creeks and streams,
           urban areas, highways, streets and underpasses, as
           well as other poor drainage and low lying areas.

* Some locations that will experience flash flooding include...
  Aurora, Joliet, Naperville, Bolingbrook, Romeoville, Plainfield, 
  St. Charles, Oswego, Batavia, Lockport, Geneva, Yorkville, Campton 
  Hills, Crest Hill, Montgomery, North Aurora, Sugar Grove, Boulder 
  Hill, Elburn and Fairmont.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Expect flooding of creeks, ditches, canals, and storm sewers, as 
well roadways, underpasses, and other poor drainage areas.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

&&

LAT...LON 4190 8860 4191 8832 4184 8826 4176 8819
      4173 8815 4157 8798 4157 8834 4169 8850

FLASH FLOOD...RADAR INDICATED

$$

Birk

2 follow-up statements

701 
WGUS73 KLOT 260329
FFSLOT

Flash Flood Statement
National Weather Service Chicago IL
1029 PM CDT Wed Aug 25 2021

ILC043-089-093-197-260800-
/O.CON.KLOT.FF.W.0010.000000T0000Z-210826T0800Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
DuPage IL-Kane IL-Kendall IL-Will IL-
1029 PM CDT Wed Aug 25 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 3 AM CDT THURSDAY FOR 
SOUTHWESTERN DUPAGE, SOUTHERN KANE, NORTHEASTERN KENDALL AND 
NORTHWESTERN WILL COUNTIES...

At 1029 PM CDT, doppler radar indicated that the heavy rain 
producing thunderstorms have abated across the warned area. However, 
between 2 and 4 inches of rain have fallen over the past few hours, 
with the highest amounts in the Sugar Grove area. Flash flooding is 
ongoing or expected to begin shortly.

HAZARD...Flash flooding.

SOURCE...Radar.

IMPACT...Rapid-onset flooding of small creeks and streams, urban
         areas, highways, streets and underpasses, as well as
         other poor drainage and low lying areas.

Some locations that will experience flash flooding include...
  Aurora, Joliet, Naperville, Bolingbrook, Romeoville, Plainfield, 
  St. Charles, Oswego, Batavia, Lockport, Geneva, Yorkville, Campton 
  Hills, Crest Hill, Montgomery, North Aurora, Sugar Grove, Boulder 
  Hill, Elburn and Fairmont.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Expect flooding of creeks, ditches, canals, and storm sewers, as 
well roadways, underpasses, and other poor drainage areas.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

&&

LAT...LON 4190 8860 4191 8832 4176 8822 4170 8819
      4157 8798 4157 8822 4169 8850 4172 8851

FLASH FLOOD...RADAR INDICATED

$$

Birk

423 
WGUS73 KLOT 260638
FFSLOT

Flash Flood Statement
National Weather Service Chicago IL
138 AM CDT Thu Aug 26 2021

ILC043-089-093-197-260648-
/O.CAN.KLOT.FF.W.0010.000000T0000Z-210826T0800Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
DuPage IL-Kane IL-Kendall IL-Will IL-
138 AM CDT Thu Aug 26 2021

...FLASH FLOOD WARNING FOR SOUTHWESTERN DUPAGE, SOUTHERN KANE, 
NORTHEASTERN KENDALL AND NORTHWESTERN WILL COUNTIES HAS BEEN 
REPLACED WITH A FLOOD ADVISORY...

The earlier heavy rain has ended. The threat for Flash Flooding has 
ended as a result. However, runoff over low spots may remain for a 
few more hours. 

LAT...LON 4190 8860 4191 8832 4176 8822 4170 8819
      4157 8798 4157 8822 4169 8850 4172 8851

$$

Carlaw

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 25, 7:21 PM CDT	Flash Flood Warning	LOT	Cook, DuPage	3 hr
Aug 25, 7:33 PM CDT	Special Marine Warning	LOT		117 min
Aug 25, 8:34 PM CDT	Areal Flood Advisory	LOT	Cook, Kankakee, Will	3 hr
Aug 25, 8:43 PM CDT	Special Weather Statement	LOT	Kankakee	47 min
Aug 25, 8:54 PM CDT	Areal Flood Advisory	LOT	DuPage, Kane, Kendall, Will	17 min
Aug 25, 9:15 PM CDT	Flash Flood Warning	LOT	Cook, Kankakee, Will	4 hr
Aug 26, 1:38 AM CDT	Areal Flood Advisory	LOT	Kane, Kendall	2 hr
Aug 26, 5:30 PM CDT	Special Weather Statement	LOT	Cook	30 min

Nearby

Flash Flood Warnings in Illinois, 2021 Every flash flood warning 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.