Alert archive / Illinois / Tornado Watches in 2004
Tornado Watch 242
The Storm Prediction Center issued this tornado watch at May 21, 2004, 5:35 PM CDT for 27 counties in Illinois; 5 counties in Indiana; Lafayette County, Wisconsin. It was in force for 5 hr.
The area
The outline as issued.
The facts
- Issued
- May 21, 2004, 5:35 PM CDT (22:35 UTC)
- Expired
- May 21, 2004, 11:00 PM CDT
- In force
- 5 hr
- Issued by
- the Storm Prediction Center
All 33 counties
Boone County, IL, Bureau County, IL, Carroll County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Grundy County, IL, Henry County, IL, Iroquois County, IL, Jo Daviess County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Marshall County, IL, McHenry County, IL, Ogle County, IL, Putnam County, IL, Stark County, IL, Stephenson County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL, Benton County, IN, Jasper County, IN, Lake County, IN, Newton County, IN, Porter County, IN, Lafayette County, WI
The radar
The Chicago radar (KLOT), 82 km from the middle of the area, began a volume at 22:38 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.
Warnings issued inside it
12 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 21, 6:45 PM CDT | Severe Thunderstorm Warning | DVN | Carroll | 60 min |
| May 21, 6:55 PM CDT | Severe Thunderstorm Warning | DVN | Whiteside | 65 min |
| May 21, 7:00 PM CDT | Severe Thunderstorm Warning | LOT | Lee, Ogle, Winnebago | 60 min |
| May 21, 7:09 PM CDT | Flash Flood Warning | LOT | Lake, McHenry | 3 hr |
| May 21, 7:13 PM CDT | Severe Thunderstorm Warning | LOT | DeKalb, Kane | 47 min |
| May 21, 7:23 PM CDT | Flash Flood Warning | LOT | Cook, DeKalb, DuPage, Kane, Lee, Ogle | 3 hr |
| May 21, 7:59 PM CDT | Severe Thunderstorm Warning | LOT | Lee, Ogle, Winnebago | 61 min |
| May 21, 8:01 PM CDT | Severe Thunderstorm Warning | LOT | DeKalb, Kane | 59 min |
| May 21, 8:03 PM CDT | Tornado Warning | LOT | DeKalb | 27 min |
| May 21, 8:22 PM CDT | Severe Thunderstorm Warning | LOT | Cook, DuPage | 53 min |
| May 21, 8:35 PM CDT | Severe Thunderstorm Warning | LOT | Cook, DuPage | 40 min |
| May 21, 9:10 PM CDT | Severe Thunderstorm Warning | LOT | Kane, Kendall | 50 min |
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, 10.6 hours before the alert went out and 190 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.
- Mixed-layer CAPE
- 2541 J/kg
- Mixed-layer CIN
- -64 J/kg
- Mixed-layer LCL
- 923 m above ground
- 0-6 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 59 m²/s²
- 0-3 km storm-relative helicity
- 99 m²/s²
- Significant tornado parameter
- 0.5
- Supercell composite
- 3.0
The text
As transmitted, in the capitals the NWS used until 2016.
000
WWUS20 KWNS 212233
SEL2
SPC WW 212235
ILZ000-INZ000-LMZ000-220400-
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 242
NWS STORM PREDICTION CENTER NORMAN OK
535 PM CDT FRI MAY 21 2004
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
NORTHERN ILLINOIS
NORTHWEST INDIANA
LAKE MICHIGAN
EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 535 PM UNTIL 1100
PM CDT.
TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS ALONG AND 60 STATUTE MILES NORTH AND
SOUTH OF A LINE FROM 70 MILES WEST SOUTHWEST OF ROCKFORD ILLINOIS
TO 45 MILES SOUTHEAST OF MEIGS FIELD ILLINOIS.
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND 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.
OTHER WATCH INFORMATION...CONTINUE...WW 235...WW 236...WW 237...WW
238...WW 239...WW 240...WW 241...
DISCUSSION...TORNADIC SUPERCELLS ERN IA EXPECTED TO DEVELOP/MOVE
E/SE VICINITY E/W BOUNDARY ACROSS NRN IL. WITH VERY UNSTABLE AIR
MASS AND VEERING SHEAR PROFILES VICINITY BOUNDARY...TORNADO THREAT
WILL CONTINUE.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
550. MEAN STORM MOTION VECTOR 27030.
...HALES
424,0902 421,0870 403,0870 405,0902SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 20, 7:32 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 21 more | 88 min |
| May 20, 9:05 PM CDT | Severe Thunderstorm Watch | SPC | Bureau, Cook, DeKalb, DuPage, Ford, Fulton and 20 more | 5 hr |
| May 21, 4:34 AM CDT | Mesoscale Discussion | SPC | Jo Daviess | 56 min |
| May 21, 9:40 AM CDT | Mesoscale Discussion | SPC | Cook, DuPage, Kane, Kankakee, Lake, Will | 2 hr |
| May 21, 10:25 AM CDT | Severe Thunderstorm Watch | SPC | Boone, Bureau, Carroll, DeKalb, Henry, Jo Daviess and 8 more | 6 hr |
| May 21, 2:45 PM CDT | Tornado Watch | SPC | Rock Island | 7 hr |
| May 21, 12:05 PM CDT | Severe Thunderstorm Watch | SPC | Adams, Allen, Blackford, DeKalb, Grant, Huntington and 7 more | 4 hr |
| May 21, 1:19 PM CDT | Mesoscale Discussion | SPC | Allen, DeKalb, Fulton, Kosciusko, Marshall, Noble and 2 more | 116 min |
| May 21, 9:44 AM CDT | Mesoscale Discussion | SPC | Adams, Buffalo, Crawford, Eau Claire, Grant, Jackson and 9 more | 3 hr |
| May 21, 1:59 PM CDT | Mesoscale Discussion | SPC | Adams, Columbia, Crawford, Dane, Dodge, Fond du Lac and 10 more | 2 hr |
| May 21, 3:00 PM CDT | Severe Thunderstorm Watch | SPC | Adams, Calumet, Columbia, Dane, Dodge, Fond du Lac and 19 more | 7 hr |
Nearby
Tornado Watches in Illinois, 2004Tornado Watches in Indiana, 2004Tornado Watches in Wisconsin, 2004Every tornado watch in 2004
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.