Alert archive / Illinois / Tornado Watches in 2015

Tornado Watch 207

May 24, 201542 counties in Illinois; 16 counties in Iowa

The Storm Prediction Center issued this tornado watch at May 24, 2015, 5:34 PM CDT for 42 counties in Illinois; 16 counties in Iowa. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: May 24, 2015, 5:34 PM CDT (22:34 UTC)
Expired: May 25, 2015, 12:06 AM CDT
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

All 58 counties

Cedar County, IA, Clinton County, IA, Des Moines County, IA, Dubuque County, IA, Henry County, IA, Jackson County, IA, Jefferson County, IA, Johnson County, IA, Jones County, IA, Lee County, IA, Linn County, IA, Louisa County, IA, Muscatine County, IA, Scott County, IA, Van Buren County, IA, Washington County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, Cass County, IL, Christian County, IL, DeKalb County, IL, DeWitt County, IL, Fulton County, IL, Hancock County, IL, Henderson County, IL, Henry County, IL, Jo Daviess County, IL, Knox County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Logan County, IL, Macon County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, McLean County, IL, Menard County, IL, Mercer County, IL, Morgan County, IL, Moultrie County, IL, Ogle County, IL, Peoria County, IL, Piatt County, IL, Putnam County, IL, Rock Island County, IL, Sangamon County, IL, Schuyler County, IL, Scott County, IL, Shelby County, IL, Stark County, IL, Stephenson County, IL, Tazewell County, IL, Warren County, IL, Whiteside County, IL, Winnebago County, IL, Woodford County, IL

The radar

The Quad Cities radar (KDVN), 28 km from the middle of the area, began a volume at 22:37 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: 40%
One or more EF2 to EF5 tornadoes: 20%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 5%
Ten or more severe hail reports: 40%
One or more hailstones of 2 inches or more: 10%
Six or more combined severe hail and wind reports: 70%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
May 24, 7:04 PM CDT	Tornado Warning Tornado observed	DVN	Mercer, Rock Island	26 min
May 24, 7:18 PM CDT	Tornado Warning Tornado observed	DVN	Scott	27 min
May 24, 11:03 PM CDT	Severe Thunderstorm Warning	ILX	Christian, Sangamon	45 min
May 24, 11:29 PM CDT	Severe Thunderstorm Warning	ILX	Macon, Moultrie, Shelby	25 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 12:00Z, 10.6 hours before the alert went out and 21 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1494 m above ground
0-6 km bulk shear: 43 kt
0-1 km storm-relative helicity: 175 m²/s²
0-3 km storm-relative helicity: 206 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.

701 
WWUS20 KWNS 242229
SEL7  
SPC WW 242229
IAZ000-ILZ000-MOZ000-250600-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 207
NWS STORM PREDICTION CENTER NORMAN OK
530 PM CDT SUN MAY 24 2015

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* TORNADO WATCH FOR PORTIONS OF 
  EASTERN IOWA
  WESTERN...CENTRAL...AND NORTHERN ILLINOIS
  FAR NORTHEAST MISSOURI

* EFFECTIVE THIS SUNDAY AFTERNOON AND MONDAY MORNING FROM 530 PM
  UNTIL 100 AM CDT.

* PRIMARY THREATS INCLUDE...
  A COUPLE TORNADOES POSSIBLE
  SCATTERED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE
  ISOLATED DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

SUMMARY...SCATTERED THUNDERSTORMS...INCLUDING A FEW SUSTAINED STORMS
AND SUPERCELLS...EXPECTED TO MOVE GENERALLY NORTHEAST ACROSS WATCH
AREA THOUGH LATE EVENING...POSING A RISK FOR SEVERE HAIL...LOCALLY
DAMAGING WIND...AND TORNADOES.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 60 MILES NORTH NORTHWEST OF
BURLINGTON IOWA TO 30 MILES SOUTHEAST OF MARSEILLES ILLINOIS. 
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU7).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 202...WW 203...WW
204...WW 205...WW 206...

AVIATION...TORNADOES AND 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
500. MEAN STORM MOTION VECTOR 22035.


...CORFIDI

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 24, 3:34 PM CDT	Mesoscale Discussion	SPC	Bureau, Carroll, Fulton, Hancock, Henderson, Henry and 17 more	56 min
May 24, 4:14 PM CDT	Tornado Watch	SPC	Adams, Alexander, Bond, Brown, Calhoun, Clinton and 16 more	8 hr
May 24, 6:04 PM CDT	Mesoscale Discussion	SPC	Alexander, Calhoun, Greene, Jackson, Jersey, Madison and 6 more	116 min
May 24, 6:41 PM CDT	Mesoscale Discussion	SPC	Bureau, Carroll, Cass, Fulton, Grundy, Hancock and 22 more	94 min

Nearby

Tornado Watches in Illinois, 2015 Tornado Watches in Iowa, 2015 Every tornado watch in 2015

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.