Alert archive / Illinois / Tornado Watches in 2017

Tornado Watch 378

June 28, 20179 counties in Illinois

The Storm Prediction Center issued this tornado watch at Jun 28, 2017, 7:06 PM CDT for 9 counties in Illinois. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Jun 28, 2017, 7:06 PM CDT (00:06 UTC)
Expired: Jun 28, 2017, 11:03 PM CDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

Counties Boone County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Kane County, IL, Lake County, IL, McHenry County, IL, Ogle County, IL, Winnebago County, IL

The radar

The Chicago radar (KLOT), 88 km from the middle of the area, began a volume at 00:06 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: 30%
One or more EF2 to EF5 tornadoes: 10%
Ten or more severe wind reports: 60%
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: 80%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Jun 28, 7:10 PM CDT	Severe Thunderstorm Warning	LOT	Boone, Winnebago	65 min
Jun 28, 7:40 PM CDT	Tornado Warning	LOT	Winnebago	20 min
Jun 28, 7:55 PM CDT	Severe Thunderstorm Warning	LOT	Boone, DeKalb, Kane, McHenry, Ogle, Winnebago	65 min
Jun 28, 8:19 PM CDT	Tornado Warning	LOT	Boone, DeKalb	26 min
Jun 28, 8:24 PM CDT	Flash Flood Warning Emergency	LOT	Boone, Winnebago	6 hr
Jun 28, 8:35 PM CDT	Severe Thunderstorm Warning	LOT	Lake	50 min
Jun 28, 8:38 PM CDT	Severe Thunderstorm Warning	LOT	Cook, DeKalb, DuPage, Kane, McHenry	52 min
Jun 28, 9:09 PM CDT	Flash Flood Warning	LOT	Lake, McHenry	6 hr

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, 0.1 hours before the alert went out and 144 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: 1521 J/kg
Mixed-layer CIN: -10 J/kg
Mixed-layer LCL: 1099 m above ground
0-6 km bulk shear: 50 kt
0-1 km storm-relative helicity: 259 m²/s²
0-3 km storm-relative helicity: 334 m²/s²
Significant tornado parameter: 2.7
Supercell composite: 15.1

Open this sounding in Storm Lab

The text

As transmitted.

222 
WWUS20 KWNS 290004
SEL8  
SPC WW 290004
ILZ000-LMZ000-290500-

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 378
NWS Storm Prediction Center Norman OK
705 PM CDT Wed Jun 28 2017

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of 
  Northern Illinois
  Lake Michigan

* Effective this Wednesday night from 705 PM until Midnight CDT.

* Primary threats include...
  A couple tornadoes possible
  Scattered damaging wind gusts to 70 mph likely
  Isolated large hail events to 1.5 inches in diameter possible

SUMMARY...Severe storms over southern Wisconsin and far northwest
Illinois  nd northeast Iowa are expected to continue moving eastward
toward southern Lake Michigan later this evening with potential to
produce damaging wind gusts and possibly a couple of tornadoes.

The tornado watch area is approximately along and 50 statute miles
east and west of a line from 30 miles northeast of Rockford IL to 50
miles south southeast of Rockford IL. For a complete depiction of
the watch see the associated watch outline update (WOUS64 KWNS
WOU8).

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 375...WW 376...WW 377...

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 27035.

...Weiss

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 28, 7:53 PM CDT	Mesoscale Discussion	SPC	Boone, Carroll, Jo Daviess, McHenry, Ogle, Stephenson and 1 more	97 min
Jun 29, 1:45 PM CDT	Mesoscale Discussion	SPC	Bond, Calhoun, Christian, Greene, Jersey, Macoupin and 8 more	2 hr

Nearby

Tornado Watches in Illinois, 2017 Every tornado 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.