Alert archive / Illinois / Severe Thunderstorm Watches in 2017

Severe Thunderstorm Watch 479

September 4, 201735 counties in Illinois; 14 counties in Missouri

The Storm Prediction Center issued this severe thunderstorm watch at Sep 4, 2017, 4:00 PM CDT for 35 counties in Illinois; 14 counties in Missouri. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued
Sep 4, 2017, 4:00 PM CDT (21:00 UTC)
Expired
Sep 4, 2017, 10:00 PM CDT
In force
6 hr
Issued by
the Storm Prediction Center
Largest hail expected
1.5 in
Strongest gust expected
60 kt
All 49 counties

Bond County, IL, Calhoun County, IL, Champaign County, IL, Christian County, IL, Clark County, IL, Clay County, IL, Clinton County, IL, Coles County, IL, Crawford County, IL, Cumberland County, IL, Douglas County, IL, Edgar County, IL, Effingham County, IL, Fayette County, IL, Greene County, IL, Jasper County, IL, Jersey County, IL, Lawrence County, IL, Macon County, IL, Macoupin County, IL, Madison County, IL, Marion County, IL, Monroe County, IL, Montgomery County, IL, Morgan County, IL, Moultrie County, IL, Piatt County, IL, Randolph County, IL, Richland County, IL, Saint Clair County, IL, Sangamon County, IL, Scott County, IL, Shelby County, IL, Vermilion County, IL, Washington County, IL, City of Saint Louis, MO, Cole County, MO, Crawford County, MO, Franklin County, MO, Gasconade County, MO, Jefferson County, MO, Lincoln County, MO, Osage County, MO, Saint Charles County, MO, Saint Francois County, MO, Saint Louis County, MO, Sainte Genevieve County, MO, Warren County, MO, Washington County, MO

The radar

The Lincoln radar (KILX), 108 km from the middle of the area, began a volume at 21:05 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
10%
One or more EF2 to EF5 tornadoes
2%
Ten or more severe wind reports
40%
One or more gusts of 65 knots or more
10%
Ten or more severe hail reports
30%
One or more hailstones of 2 inches or more
10%
Six or more combined severe hail and wind reports
70%

Warnings issued inside it

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

IssuedProductOfficeCountiesLasted
Sep 4, 4:21 PM CDTSevere Thunderstorm WarningILXMorgan, Sangamon24 min
Sep 4, 4:23 PM CDTSevere Thunderstorm WarningILXSangamon38 min
Sep 4, 4:25 PM CDTSevere Thunderstorm WarningLSXGreene, Macoupin, Montgomery65 min
Sep 4, 5:15 PM CDTSevere Thunderstorm WarningLSXJersey, Macoupin, Montgomery60 min
Sep 4, 5:22 PM CDTSevere Thunderstorm WarningILXMacon, Moultrie, Piatt, Shelby38 min
Sep 4, 6:11 PM CDTSevere Thunderstorm WarningLSXBond, Jersey, Macoupin, Madison, Montgomery64 min
Sep 4, 6:25 PM CDTSevere Thunderstorm WarningLSXLincoln, Saint Charles, Warren50 min
Sep 4, 6:53 PM CDTSevere Thunderstorm WarningLSXBond, Clinton, Madison, Saint Clair82 min
Sep 4, 7:08 PM CDTSevere Thunderstorm WarningLSXFranklin, Jefferson, Saint Charles, Saint Louis, Warren52 min
Sep 4, 7:47 PM CDTSevere Thunderstorm WarningLSXMonroe43 min
Sep 4, 7:55 PM CDTSevere Thunderstorm WarningLSXClinton, Saint Clair, Washington41 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, 9.0 hours before the alert went out and 101 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 2017-09-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 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 2017-09-04The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 220 square meters per square second.193958Sfc1 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1674 m above ground
0-6 km bulk shear
30 kt
0-1 km storm-relative helicity
220 m²/s²
0-3 km storm-relative helicity
241 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 4, 2:17 PM CDTMesoscale DiscussionSPCChampaign, Douglas, Edgar, Ford, Iroquois, Vermilion118 min
Sep 4, 3:43 PM CDTMesoscale DiscussionSPCChampaign, Christian, DeWitt, Douglas, Ford, Greene and 16 more2 hr
Sep 4, 6:05 PM CDTMesoscale DiscussionSPCBond, Calhoun, Champaign, Christian, Clark, Clay and 28 more115 min

Nearby

Severe Thunderstorm Watches in Illinois, 2017Severe Thunderstorm Watches in Missouri, 2017Every severe thunderstorm watch in 2017

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.