Alert archive / Illinois / Mesoscale Discussions in 2018

Mesoscale Discussion 1325

August 20, 20186 states

The Storm Prediction Center issued this mesoscale discussion at Aug 20, 2018, 11:46 AM CDT for 6 states. It was in force for 119 min.

The area

The outline as issued.

The facts

Issued: Aug 20, 2018, 11:46 AM CDT (16:46 UTC)
Expired: Aug 20, 2018, 1:45 PM CDT
In force: 119 min
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 91 counties

Arkansas County, AR, Clay County, AR, Craighead County, AR, Crittenden County, AR, Cross County, AR, Greene County, AR, Independence County, AR, Jackson County, AR, Jefferson County, AR, Lawrence County, AR, Lee County, AR, Lonoke County, AR, Mississippi County, AR, Monroe County, AR, Phillips County, AR, Poinsett County, AR, Prairie County, AR, Randolph County, AR, Sharp County, AR, St. Francis County, AR, White County, AR, Woodruff County, AR, Alexander County, IL, Bond County, IL, Clay County, IL, Clinton County, IL, Franklin County, IL, Hamilton County, IL, Jackson County, IL, Jefferson County, IL, Johnson County, IL, Madison County, IL, Marion County, IL, Massac County, IL, Monroe County, IL, Perry County, IL, Pope County, IL, Pulaski County, IL, Randolph County, IL, Saint Clair County, IL, Saline County, IL, Union County, IL, Washington County, IL, Wayne County, IL, Williamson County, IL, Ballard County, KY, Carlisle County, KY, Fulton County, KY, Graves County, KY, Hickman County, KY, McCracken County, KY, Bollinger County, MO, Butler County, MO, Cape Girardeau County, MO, Carter County, MO, City of Saint Louis, MO, Dunklin County, MO, Iron County, MO, Jefferson County, MO, Madison County, MO, Mississippi County, MO, New Madrid County, MO, Oregon County, MO, Pemiscot County, MO, Perry County, MO, Reynolds County, MO, Ripley County, MO, Saint Francois County, MO, Saint Louis County, MO, Sainte Genevieve County, MO, Scott County, MO, Stoddard County, MO, Washington County, MO, Wayne County, MO, Coahoma County, MS, DeSoto County, MS, Marshall County, MS, Panola County, MS, Quitman County, MS, Tate County, MS, Tunica County, MS, Crockett County, TN, Dyer County, TN, Fayette County, TN, Gibson County, TN, Haywood County, TN, Lake County, TN, Lauderdale County, TN, Obion County, TN, Shelby County, TN, Tipton County, TN

The radar

The Paducah radar (KPAH), 123 km from the middle of the area, began a volume at 16:48 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 344Aug 20, 12:45 PM CDT

The nearest sounding before it

Little Rock, AR (KBYH), launched 12:00Z, 4.8 hours before the alert went out and 215 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: 904 J/kg
Mixed-layer CIN: -46 J/kg
Mixed-layer LCL: 737 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 81 m²/s²
0-3 km storm-relative helicity: 133 m²/s²
Significant tornado parameter: 0.5
Supercell composite: 3.7

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 20, 12:46 PM CDT	Severe Thunderstorm Watch	SPC	Baxter, Clay, Cleburne, Craighead, Crittenden, Cross and 21 more	7 hr
Aug 20, 3:14 PM CDT	Mesoscale Discussion	SPC	Ashley, Chicot	3 hr
Aug 20, 4:00 PM CDT	Mesoscale Discussion	SPC	Clay, Cleburne, Craighead, Crittenden, Cross, Greene and 16 more	2 hr
Aug 20, 5:57 PM CDT	Mesoscale Discussion	SPC	Ashley, Chicot	63 min
Aug 20, 4:45 PM CDT	Severe Thunderstorm Watch	SPC	Gallatin, Hardin, Massac, Pope	6 hr
Aug 20, 4:46 PM CDT	Mesoscale Discussion	SPC	Boone, Carroll, Cook, DeKalb, DuPage, Grundy and 11 more	119 min

Nearby

Mesoscale Discussions in Illinois, 2018 Mesoscale Discussions in Missouri, 2018 Mesoscale Discussions in Arkansas, 2018 Every mesoscale discussion in 2018

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.