Alert archive / Illinois / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 616

September 4, 201219 counties in Illinois; 6 counties in Iowa

The Storm Prediction Center issued this severe thunderstorm watch at Sep 4, 2012, 8:51 PM CDT for 19 counties in Illinois; 6 counties in Iowa. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued
Sep 4, 2012, 8:51 PM CDT (01:51 UTC)
Expired
Sep 5, 2012, 2:00 AM CDT
In force
5 hr
Issued by
the Storm Prediction Center
Largest hail expected
1.5 in
Strongest gust expected
60 kt
All 25 counties

Buchanan County, IA, Clinton County, IA, Delaware County, IA, Dubuque County, IA, Jackson County, IA, Jones County, IA, Boone County, IL, Carroll County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Grundy County, IL, Jo Daviess County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, McHenry County, IL, Ogle County, IL, Stephenson County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL

The radar

The Milwaukee radar (KMKX), 104 km from the middle of the area, began a volume at 01:52 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
30%
One or more gusts of 65 knots or more
30%
Ten or more severe hail reports
30%
One or more hailstones of 2 inches or more
20%
Six or more combined severe hail and wind reports
60%

Warnings issued inside it

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

IssuedProductOfficeCountiesLasted
Sep 4, 9:45 PM CDTSevere Thunderstorm WarningLOTBoone, Cook, DeKalb, DuPage, Kane, Lake and 4 more60 min
Sep 4, 10:35 PM CDTSevere Thunderstorm WarningLOTCook, DeKalb, DuPage, Grundy, Kane, Kendall and 5 more70 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

Davenport, (KDVN), launched 00:00Z, 1.9 hours before the alert went out and 121 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, Davenport, at 00:00Z on 2012-09-05Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1890 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, Davenport, at 00:00Z on 2012-09-05The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -23 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
1890 J/kg
Mixed-layer CIN
-49 J/kg
Mixed-layer LCL
1662 m above ground
0-6 km bulk shear
32 kt
0-1 km storm-relative helicity
-23 m²/s²
0-3 km storm-relative helicity
44 m²/s²
Significant tornado parameter
-0.0
Supercell composite
-0.9

Open this sounding in Storm Lab

The text

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

462 
WWUS20 KWNS 050147
SEL6
SPC WW 050147
IAZ000-ILZ000-LMZ000-050700-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 616
NWS STORM PREDICTION CENTER NORMAN OK
850 PM CDT TUE SEP 4 2012

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

       EAST CENTRAL IOWA
       NORTHERN ILLINOIS
       LAKE MICHIGAN

EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 850 PM
UNTIL 200 AM CDT.

HAIL TO 1.5 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 30
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES SOUTH OF
DUBUQUE IOWA TO 105 MILES EAST OF ROCKFORD ILLINOIS.  FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU6).

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...CONTINUE...WW 614...WW 615...

DISCUSSION...THE MCS OVER SE WI HAS SHOWN A TENDENCY TO ACCELERATE
SEWD IN THE PAST HOUR...WHILE UPSTREAM SEVERE STORMS ACROSS SW WI/NE
IA SHOULD LIKEWISE MOVE SEWD WITH THE COMPOSITE OUTFLOW BOUNDARY.
GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES AND MLCAPE AOA 2000
J/KG PER 00Z DVN SOUNDING...THE THREAT FOR AT LEAST ISOLATED
DAMAGING WINDS/LARGE HAIL SHOULD SPREAD INTO NRN IL BEFORE THE
STORMS WEAKEN LATER TONIGHT.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM
MOTION VECTOR 31025.


...THOMPSON

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 4, 8:30 PM CDTMesoscale DiscussionSPCJo Daviess60 min
Sep 5, 1:14 AM CDTMesoscale DiscussionSPCCarroll, Henry, Jo Daviess, Rock Island, Stephenson, Whiteside and 1 more91 min
Sep 5, 3:43 AM CDTMesoscale DiscussionSPCBoone, Bureau, Carroll, DeKalb, Grundy, Henderson and 21 more92 min
Sep 5, 9:04 AM CDTMesoscale DiscussionSPCAlexander, Bond, Clark, Clay, Clinton, Crawford and 28 more86 min
Sep 5, 9:37 AM CDTSevere Thunderstorm WatchSPCBond, Clark, Clay, Clinton, Coles, Crawford and 24 more6 hr
Sep 5, 1:10 PM CDTMesoscale DiscussionSPCGallatin, Hardin, Johnson, Massac, Pope65 min
Sep 5, 1:43 PM CDTSevere Thunderstorm WatchSPCHardin5 hr
Sep 5, 2:13 PM CDTMesoscale DiscussionSPCAlexander, Massac, Pulaski2 hr
Sep 5, 2:29 PM CDTSevere Thunderstorm WatchSPCAlexander, Johnson, Massac, Pope, Pulaski, Union8 hr
Sep 5, 4:02 PM CDTMesoscale DiscussionSPCBoone, Carroll, Cook, DeKalb, DuPage, Jo Daviess and 7 more88 min
Sep 4, 7:27 PM CDTMesoscale DiscussionSPCBuena Vista, Cherokee, Clay, Dickinson, Lyon, O'Brien and 3 more63 min
Sep 4, 7:45 PM CDTSevere Thunderstorm WatchSPCBuena Vista, Cherokee, Clay, Dickinson, Ida, Lyon and 5 more6 hr
Sep 4, 9:51 PM CDTMesoscale DiscussionSPCBuena Vista, Calhoun, Cerro Gordo, Clay, Dickinson, Emmet and 12 more54 min
Sep 4, 10:19 PM CDTSevere Thunderstorm WatchSPCBlack Hawk, Bremer, Butler, Calhoun, Cerro Gordo, Emmet and 14 more5 hr
Sep 4, 11:16 PM CDTSevere Thunderstorm WatchSPCAllamakee, Chickasaw, Clayton, Fayette, Floyd, Howard and 2 more4 hr

Nearby

Severe Thunderstorm Watches in Illinois, 2012Severe Thunderstorm Watches in Iowa, 2012Every 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.