Alert archive / Illinois / Special Weather Statements in 2021

Special Weather Statement, NWS Chicago, IL

August 18, 2021Will County, Illinois

NWS Chicago, IL issued this special weather statement at Aug 18, 2021, 3:21 PM CDT for Will County, Illinois. It was in force for 39 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued
Aug 18, 2021, 3:21 PM CDT (20:21 UTC)
Expired
Aug 18, 2021, 4:00 PM CDT
In force
39 min
Issued by
NWS Chicago, IL
Hail
0.25 in
Wind
40

County Will County, IL

The radar

The Chicago radar (KLOT), 31 km from the middle of the area, began a volume at 20:20 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, 8.4 hours before the alert went out and 166 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 2021-08-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 558 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 2021-08-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 5 square meters per square second.19395878Sfc1 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
558 J/kg
Mixed-layer CIN
-35 J/kg
Mixed-layer LCL
850 m above ground
0-6 km bulk shear
19 kt
0-1 km storm-relative helicity
5 m²/s²
0-3 km storm-relative helicity
22 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

538 
WWUS83 KLOT 182021
SPSLOT

Special Weather Statement
National Weather Service Chicago/Romeoville
321 PM CDT Wed Aug 18 2021
 
ILZ105-182100-
Southern Cook IL-
321 PM CDT Wed Aug 18 2021

...A strong thunderstorm will impact portions of south central Cook
County through 400 PM CDT...

At 320 PM CDT, Doppler radar was tracking a strong thunderstorm over
Matteson. This storm was nearly stationary.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around 
         unsecured objects. Minor damage to outdoor objects is 
         possible.

Locations impacted include...
Tinley Park, Park Forest, Homewood, Matteson, Country Club Hills,
Hazel Crest, Richton Park, Flossmoor and Olympia Fields.

Including the following interstate...
 I-57 between mile markers 339 and 343.
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building. 

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 4147 8773 4147 8778 4149 8779 4154 8779
      4157 8768 4148 8768
TIME...MOT...LOC 2020Z 159DEG 1KT 4151 8776 

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

$$

RATZER

The office that day

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

IssuedProductOfficeCountiesLasted
Aug 18, 1:33 PM CDTAreal Flood AdvisoryLOTWill93 min
Aug 18, 5:47 PM CDTAreal Flood AdvisoryLOTBenton118 min

Nearby

Special Weather Statements in Illinois, 2021Every special weather statement 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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.