Alert archive / Illinois / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 233

May 3, 201218 counties in Illinois; 5 counties in Indiana

The Storm Prediction Center issued this severe thunderstorm watch at May 3, 2012, 6:41 PM CDT for 18 counties in Illinois; 5 counties in Indiana. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: May 3, 2012, 6:41 PM CDT (23:41 UTC)
Expired: May 4, 2012, 12:00 AM CDT
In force: 5 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 23 counties

Boone County, IL, Cook County, IL, DeKalb 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, Lee County, IL, Livingston County, IL, McHenry County, IL, Ogle County, IL, Will County, IL, Winnebago County, IL, Benton County, IN, Jasper County, IN, Lake County, IN, Newton County, IN, Porter County, IN

The radar

The Chicago radar (KLOT), 20 km from the middle of the area, began a volume at 23:42 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 SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 20%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 30%
Ten or more severe hail reports: 50%
One or more hailstones of 2 inches or more: 30%
Six or more combined severe hail and wind reports: 70%

Warnings issued inside it

6 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
May 3, 7:08 PM CDT	Severe Thunderstorm Warning	LOT	Cook	67 min
May 3, 7:23 PM CDT	Flash Flood Warning	LOT	Cook, DuPage	4 hr
May 3, 8:00 PM CDT	Severe Thunderstorm Warning	LOT	Cook, DuPage	75 min
May 3, 8:07 PM CDT	Severe Thunderstorm Warning	LOT	LaSalle, Livingston	68 min
May 3, 9:50 PM CDT	Severe Thunderstorm Warning	LOT	Cook, Will	55 min
May 3, 10:10 PM CDT	Flash Flood Warning	LOT	Cook	5 hr

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 11.7 hours before the alert went out and 182 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: 1717 J/kg
Mixed-layer CIN: -76 J/kg
Mixed-layer LCL: 775 m above ground
0-6 km bulk shear: 25 kt
0-1 km storm-relative helicity: 122 m²/s²
0-3 km storm-relative helicity: 49 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

016 
WWUS20 KWNS 032341
SEL3
SPC WW 032341
ILZ000-INZ000-LMZ000-040500-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 233
NWS STORM PREDICTION CENTER NORMAN OK
645 PM CDT THU MAY 3 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

       NORTHEAST ILLINOIS
       EXTREME NORTHWEST INDIANA
       LAKE MICHIGAN

EFFECTIVE THIS THURSDAY NIGHT FROM 645 PM UNTIL MIDNIGHT CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 50
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES NORTHWEST
OF MARSEILLES ILLINOIS TO 10 MILES NORTH OF VALPARAISO INDIANA.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU3).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...THIS SEVERE THUNDERSTORM WATCH REPLACES
SEVERE THUNDERSTORM WATCH NUMBER 230. WATCH NUMBER 230 WILL NOT
BE IN EFFECT AFTER 645 PM CDT. CONTINUE...WW 231...WW 232...

DISCUSSION...RENEWED THUNDERSTORM DEVELOPMENT IS UNDERWAY ALONG A
CONFLUENCE BAND ACROSS NE IL...WITH THE CONVECTION BEING FED BY 30
KT SWLY LOW-LEVEL FLOW AND RICHER MOISTURE/INSTABILITY ACROSS
CENTRAL IL.  THE COMBINATION OF MODERATE INSTABILITY AND EFFECTIVE
BULK SHEAR OF 30-40 KT WILL SUPPORT ORGANIZED CLUSTERS AND SUPERCELL
STRUCTURES...WITH A PRIMARY RISK OF LARGE HAIL AND DAMAGING WINDS
THROUGH EARLY TONIGHT.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 26025.


...THOMPSON

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 3, 1:07 PM CDT	Severe Thunderstorm Watch	SPC	Boone, Cook, DeKalb, DuPage, Kane, Kendall and 5 more	6 hr
May 3, 2:53 PM CDT	Mesoscale Discussion	SPC	Boone, Cook, DeKalb, DuPage, Kane, Lake and 3 more	67 min
May 3, 3:53 PM CDT	Mesoscale Discussion	SPC	Brown, Bureau, Cass, DeWitt, Fulton, Greene and 22 more	37 min
May 3, 4:20 PM CDT	Tornado Watch	SPC	Bureau, Cass, Champaign, DeWitt, Ford, Fulton and 26 more	8 hr
May 3, 6:22 PM CDT	Mesoscale Discussion	SPC	Cook, DeKalb, DuPage, Kane, Kendall, Lake and 1 more	23 min
May 3, 6:42 PM CDT	Mesoscale Discussion	SPC	Adams, Brown, Cass, DeWitt, Fulton, Greene and 17 more	63 min

Nearby

Severe Thunderstorm Watches in Illinois, 2012 Severe Thunderstorm Watches in Indiana, 2012 Every severe thunderstorm watch in 2012

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.