Alert archive / Illinois / Flash Flood Warnings in 2021

Flash Flood Warning 7, NWS Chicago, IL

August 24, 2021Boone County, McHenry County, Illinois

NWS Chicago, IL issued this flash flood warning at Aug 24, 2021, 5:40 PM CDT for Boone County, McHenry County, Illinois. It was in force for 4 hr. 2 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 24, 2021, 5:40 PM CDT (22:40 UTC)
Expired: Aug 24, 2021, 9:45 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

The radar

The Milwaukee radar (KMKX), 63 km from the middle of the area, began a volume at 22:42 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 24, 6:45 PM CDT	FLASH FLOOD	Harvard, IL	DELAYED REPORT OF ONE CAR STALLED DUE TO FLOODWATERS ON MCKINLEY STREET IN HARVARD. TIME ESTIMATED.
Aug 24, 9:17 PM CDT	HEAVY RAIN 2.06	1 Ese Harvard, IL	STORM TOTAL. 1.49 INCHES FELL OVER A ONE HOUR PERIOD BETWEEN 6:14 AND 7:14 PM. PERSONAL WEATHER STATION KILHARVA3.

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

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 10.7 hours before the alert went out and 175 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: 1809 J/kg
Mixed-layer CIN: -127 J/kg
Mixed-layer LCL: 1284 m above ground
0-6 km bulk shear: 15 kt
0-1 km storm-relative helicity: 35 m²/s²
0-3 km storm-relative helicity: 9 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

888 
WGUS53 KLOT 242240
FFWLOT
ILC007-111-250245-
/O.NEW.KLOT.FF.W.0007.210824T2240Z-210825T0245Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Chicago IL
540 PM CDT Tue Aug 24 2021

The National Weather Service in Chicago has issued a

* Flash Flood Warning for...
  Northeastern Boone County in north central Illinois...
  Northwestern McHenry County in northeastern Illinois...

* Until 945 PM CDT.

* At 540 PM CDT, doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. An estimated 2 to 3 inches of 
  rain have fallen, with isolated higher amounts. Although rainfall 
  is diminishing in intensity, additional storms are expected to 
  move into the area shortly. Rainfall rates in excess of 1 inch per 
  hour will be possible, causing additional rainfall amounts up to 
  1.5 inches.

  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...
  Harvard, Capron, Hebron and Chemung.

The heaviest rainfall has occurred in the headwaters of Piscasaw 
Creek north of Chemung and Harvard. Rapid water level rises along 
Piscasaw Creek and tributaries may be imminent.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Flash Flood Warning means rapid-onset flooding is imminent or may 
already be occurring. Persons along creeks, drainage ditches, and 
other waterways should take immediate precautions to protect life 
and property.

Expect flooding of creeks, ditches, farmland, roadways, and and 
other low lying areas.

&&

LAT...LON 4236 8881 4244 8877 4249 8872 4249 8836
      4237 8851 4233 8871

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL...1 INCH IN 1 HOUR

$$

WSL

2 follow-up statements

801 
WGUS73 KLOT 250024
FFSLOT

Flash Flood Statement
National Weather Service Chicago IL
724 PM CDT Tue Aug 24 2021

ILC007-111-250245-
/O.CON.KLOT.FF.W.0007.000000T0000Z-210825T0245Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boone IL-McHenry IL-
724 PM CDT Tue Aug 24 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 945 PM CDT THIS 
EVENING FOR NORTHEASTERN BOONE AND NORTHWESTERN MCHENRY COUNTIES...

At 724 PM CDT, doppler radar and automated rain gauges indicated 
thunderstorms had produced heavy rain across the warned area. 
Between 2 and 5 inches of rain have fallen. Although the heaviest 
rainfall had moved east out of the area, light rainfall may 
continue, with additional rainfall amounts up to 0.5 inches possible.

HAZARD...Flash flooding.

SOURCE...Radar and automated gauges.

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...
  Harvard, Capron, Hebron and Chemung.

The heaviest rainfall has occurred in the headwaters of Piscasaw 
Creek north of Chemung and Harvard. A rapid rise in water levels 
along Piscasaw Creek and nearby waterways is imminent.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Flash Flood Warning means rapid-onset flooding is imminent or may 
already be occurring. Persons along creeks, drainage ditches, and 
other waterways should take immediate precautions to protect life 
and property.

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

&&

LAT...LON 4236 8881 4244 8877 4249 8872 4249 8836
      4237 8851 4233 8871

FLASH FLOOD...RADAR AND GAUGE INDICATED

$$

WSL

089 
WGUS73 KLOT 250242
FFSLOT

Flash Flood Statement
National Weather Service Chicago IL
942 PM CDT Tue Aug 24 2021

ILC007-111-250252-
/O.EXP.KLOT.FF.W.0007.000000T0000Z-210825T0245Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boone IL-McHenry IL-
942 PM CDT Tue Aug 24 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 945 PM CDT THIS EVENING FOR 
NORTHEASTERN BOONE AND NORTHWESTERN MCHENRY COUNTIES...

Flooding is no longer expected to pose a threat. Please continue to 
heed remaining road closures.

LAT...LON 4236 8881 4244 8877 4249 8872 4249 8836
      4237 8851 4233 8871

$$

Birk

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 24, 3:19 AM CDT	Heat Advisory	LOT	Cook, DeKalb, Ford, Grundy, Iroquois, Kankakee and 6 more	17 hr
Aug 24, 3:30 PM CDT	Special Marine Warning	LOT		60 min
Aug 24, 4:21 PM CDT	Special Weather Statement	LOT	Boone	24 min
Aug 24, 4:33 PM CDT	Heat Advisory	LOT	Ford, Grundy, Iroquois, Kankakee, LaSalle, Livingston and 1 more	26 hr
Aug 24, 4:58 PM CDT	Areal Flood Advisory	LOT	Boone, Lake, McHenry	3 hr
Aug 24, 5:13 PM CDT	Special Weather Statement	LOT	DuPage	32 min
Aug 24, 5:26 PM CDT	Severe Thunderstorm Warning	LOT	Boone, Lee, Ogle, Winnebago	64 min
Aug 24, 5:28 PM CDT	Special Marine Warning	LOT		92 min
Aug 24, 6:09 PM CDT	Severe Thunderstorm Warning	LOT	Boone, DeKalb, Kane, Lee, McHenry, Ogle	66 min
Aug 24, 6:13 PM CDT	Beach Hazards Statement	LOT	Cook, Lake	4 hr
Aug 24, 6:19 PM CDT	Areal Flood Advisory	LOT	Cook, DuPage, Lake	17 min
Aug 24, 6:36 PM CDT	Flash Flood Warning	LOT	Cook, DuPage, Lake	3 hr
Aug 24, 6:54 PM CDT	Special Weather Statement	LOT	Kendall, LaSalle	51 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.