Alert archive / Illinois / Tornado Watches in 2020

Tornado Watch 73

March 28, 202033 counties in Illinois

The Storm Prediction Center issued this tornado watch at Mar 28, 2020, 8:41 PM CDT for 33 counties in Illinois. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Mar 28, 2020, 8:41 PM CDT (01:41 UTC)
Expired: Mar 28, 2020, 11:19 PM CDT
In force: 3 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 50 kt

All 33 counties

Bureau County, IL, Cass County, IL, Champaign County, IL, Christian County, IL, DeKalb County, IL, DeWitt County, IL, Ford County, IL, Grundy County, IL, Iroquois County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Logan County, IL, Macon County, IL, Marshall County, IL, Mason County, IL, McLean County, IL, Menard County, IL, Morgan County, IL, Ogle County, IL, Peoria County, IL, Piatt County, IL, Putnam County, IL, Sangamon County, IL, Stark County, IL, Tazewell County, IL, Vermilion County, IL, Will County, IL, Winnebago County, IL, Woodford County, IL

The radar

The Lincoln radar (KILX), 62 km from the middle of the area, began a volume at 01:39 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: 30%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 20%
One or more hailstones of 2 inches or more: 20%
Six or more combined severe hail and wind reports: 60%

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
Mar 28, 8:53 PM CDT	Tornado Warning	LOT	Lee, Ogle	37 min
Mar 28, 8:56 PM CDT	Tornado Warning	ILX	Peoria, Tazewell, Woodford	28 min
Mar 28, 9:19 PM CDT	Tornado Warning	LOT	Ogle, Winnebago	26 min
Mar 28, 9:39 PM CDT	Severe Thunderstorm Warning	ILX	Woodford	15 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 00:00Z, 1.7 hours before the alert went out and 76 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: 730 J/kg
Mixed-layer CIN: -64 J/kg
Mixed-layer LCL: 861 m above ground
0-6 km bulk shear: 81 kt
0-1 km storm-relative helicity: 445 m²/s²
0-3 km storm-relative helicity: 445 m²/s²
Significant tornado parameter: 2.2
Supercell composite: 15.8

Open this sounding in Storm Lab

The text

As transmitted.

610 
WWUS20 KWNS 290138
SEL3  
SPC WW 290138
ILZ000-LMZ000-290700-

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 73
NWS Storm Prediction Center Norman OK
840 PM CDT Sat Mar 28 2020

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of 
  Northern and central Illinois
  Lake Michigan

* Effective this Saturday night and Sunday morning from 840 PM
  until 200 AM CDT.

* Primary threats include...
  A couple intense tornadoes possible
  Scattered damaging wind gusts to 60 mph possible
  Isolated large hail events to 1.5 inches in diameter possible

SUMMARY...Low-topped arcing line of thunderstorms will spread
rapidly east-northeast across the rest of northern and central
Illinois through at least late evening before eventually weakening
overnight.

The tornado watch area is approximately along and 65 statute miles
east and west of a line from 15 miles south of Decatur IL to 10
miles northeast of Rockford IL. For a complete depiction of the
watch see the associated watch outline update (WOUS64 KWNS WOU3).

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...This tornado watch replaces tornado
watch number 69. Watch number 69 will not be in effect after 840
PM CDT. CONTINUE...WW 70...WW 71...WW 72...

AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 1.5 inches. Extreme turbulence and surface wind
gusts to 50 knots. A few cumulonimbi with maximum tops to 350. Mean
storm motion vector 25045.

...Grams

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Mar 28, 8:06 PM CDT	Mesoscale Discussion	SPC	Bureau, Carroll, Cass, DeKalb, DeWitt, Grundy and 17 more	54 min
Mar 28, 10:23 PM CDT	Mesoscale Discussion	SPC	DeKalb, Ford, Grundy, Kendall, LaSalle, Livingston and 1 more	97 min

Nearby

Tornado Watches in Illinois, 2020 Every tornado watch in 2020

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.