Alert archive / Illinois / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 18, NWS Chicago, IL

February 28, 20174 counties in Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Feb 28, 2017, 8:35 PM CST for 4 counties in Illinois. It was in force for 40 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Feb 28, 2017, 8:35 PM CST (02:35 UTC)
Expired: Feb 28, 2017, 9:15 PM CST
In force: 40 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Hail: 1.0 in
Wind: 60.0 mph

Counties DeKalb County, IL, Kendall County, IL, LaSalle County, IL, Lee County, IL

The watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
Feb 28, 2:57 PM CST	Tornado Watch	SPC	7 hr

The nearest sounding before it

Davenport, (KDVN), launched 00:00Z, 2.6 hours before the alert went out and 137 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: 23 J/kg
Mixed-layer CIN: -97 J/kg
Mixed-layer LCL: 1185 m above ground
0-6 km bulk shear: 46 kt
0-1 km storm-relative helicity: 124 m²/s²
0-3 km storm-relative helicity: 238 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.4

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Chicago, IL wrote its last area forecast discussion before this severe thunderstorm warning went out at Feb 28, 7:24 PM CST, 1 hour 11 minutes earlier.

Area forecast discussion, Feb 28, 7:24 PM CST, 1 hour 11 minutes before

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Hazardous weather outlook, Feb 28, 3:39 PM CST, 4 hours 56 minutes before

Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
339 PM CST Tue Feb 28 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
012145-
Winnebago-Boone-McHenry-Lake Illinois-Ogle-Lee-De Kalb-Kane-
DuPage-Cook-La Salle-Kendall-Grundy-Will-Kankakee-Livingston-
Iroquois-Ford-Lake Indiana-Porter-Newton-Jasper-Benton-
339 PM CST Tue Feb 28 2017 /439 PM EST Tue Feb 28 2017/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS...
NORTHEAST ILLINOIS AND NORTHWEST INDIANA.

.DAY ONE...Tonight.

WEATHER HAZARDS EXPECTED:
  Significant Thunderstorm Risk...with an associated:
      Elevated Tornado Risk.
      Extreme Hail Risk...larger than golf ball size.
      Significant Thunderstorm Wind Damage Risk.

DISCUSSION:

Low pressure over eastern Iowa this afternoon will move east
across northern Illinois tonight. Unseasonably mild and moist
air will continue to spread across the area this evening as a
warm front lifts north across the region ahead of the low,
which combined with strong mid and upper level winds will set
the stage for strong to severe thunderstorms across the area.
Any thunderstorm which develops in this environment will have
the potential to produce large hail, and some storms especially
this evening will likely have the potential for producing
damaging winds and isolated tornadoes. While areas south of
Interstate 88 across northern Illinois and Interstate 80 across
northwest Indiana may have a slightly higher potential to
produce damaging wind and isolated tornadoes, some threat
exists all the way north to the Wisconsin border. Storms will
initially be scattered during the late afternoon and early
evening hours, but should develop into a line which will move
slowly east across the outlook area by mid or late evening.
Storms may linger well into the overnight hours especially
south and southeast of Chicago, with the potential for
locally heavy rainfall in some of these locations.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Wednesday...
  Limited Thunderstorm Risk.
  Elevated Snow Risk.
Thursday...
  Elevated Snow Risk.
Sunday and Monday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

Spotters will likely be needed this afternoon into tonight. Due
to very fast storm motion and the likelihood of the most intense
storms in the region occurring after dark, spotters should use
extreme caution.

GENERAL STORM MOTION OF THE DAY:

Moving to the northeast or east at 40 MPH and increasing to 65 MPH
later this evening.

&&

LMZ740>745-012145-
Winthrop Harbor to Wilmette Harbor-
Wilmette Harbor to Northerly Island-
Northerly Island to Calumet Harbor-Calumet Harbor to Gary-
Gary to Burns Harbor-Burns Harbor to Michigan City-
339 PM CST Tue Feb 28 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE illinois NEARSHORE
WATERS OF LAKE MICHIGAN AND THE indiana NEARSHORE WATERS OF LAKE
MICHIGAN.

.DAY ONE...Tonight.

Hazardous Conditions for Small Craft are likely, including the
potential for severe thunderstorms this evening.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Wednesday through Friday...
  Hazardous Conditions for Small Craft are likely.
Monday...
  Hazardous Conditions for Small Craft are likely.

&&

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-012145-
Lake Michigan from Michigan City IN to St. Joseph MI 5 NM
offshore to Mid Lake-
Lake Michigan from Seul Choix Point to Rock Island Passage 5 NM
offshore to Mid Lake-
Lake Michigan South of a line from Seul Choix Point to the
Mackinac Bridge and north of a line from Charlevoix MI to South
Fox Island 5 NM offshore-
Lake Michigan from Charlevoix to Point Betsie MI 5 NM offshore to
Mid Lake-
Lake Michigan from Point Betsie to Manistee MI 5 NM offshore to
Mid Lake-
Lake Michigan from Rock Island Passage to Sturgeon Bay WI-
Lake Michigan from Sturgeon Bay to Two Rivers WI 5 NM offshore to
Mid Lake-
Lake Michigan from Two Rivers to Sheboygan WI 5 NM offshore to
Mid Lake-
Lake Michigan from Sheboygan to Port Washington WI 5 NM offshore
to Mid Lake-
Lake Michigan from Port Washington to North Point Light WI 5 NM
offshore to Mid Lake-
Lake Michigan from North Point Light to Wind Point WI 5 NM
offshore to Mid Lake-
Lake Michigan from Wind Point WI to Winthrop Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Winthrop Harbor to Wilmette Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Wilmette Harbor IL to Michigan City IN 5 NM
offshore to Mid Lake-
Lake Michigan from Pentwater to Manistee MI 5 NM offshore to Mid
Lake-
Lake Michigan from Whitehall to Pentwater MI 5 NM offshore to Mid
Lake-
Lake Michigan from Grand Haven to Whitehall MI 5 NM offshore to
Mid Lake-
Lake Michigan from Holland to Grand Haven MI 5 NM offshore to Mid
Lake-
Lake Michigan from South Haven to Holland MI 5 NM offshore to Mid
Lake-
Lake Michigan from St. Joseph to South Haven MI 5 NM offshore to
Mid Lake-
339 PM CST Tue Feb 28 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE OPEN WATERS OF LAKE
MICHIGAN.

.DAY ONE...Tonight.

Thunderstorms are likely across southern Lake Michigan tonight.
Some storms may be severe this evening and early overnight. Fog
is possible across southern parts of the Lake overnight. Gales
are likely across northern Lake Michigan late tonight.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Gale force winds are likely Wednesday and Wednesday evening.

&&

Ratzer

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In the hours before

Local storm report, Feb 28, 7:41 PM CST, 54 minutes before

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Local storm report, Feb 28, 7:57 PM CST, 38 minutes before

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Local storm report, Feb 28, 8:04 PM CST, 31 minutes before

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Local storm report, Feb 28, 8:19 PM CST, 16 minutes before

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Local storm report, Feb 28, 8:27 PM CST, 8 minutes before

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Local storm report, Feb 28, 8:30 PM CST, 5 minutes before

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The office that day

Everything else NWS Chicago, IL issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 28, 6:00 PM CST	Severe Thunderstorm Warning	LOT	Cook, Grundy, Kendall, Will	45 min
Feb 28, 6:13 PM CST	Tornado Warning	LOT	Grundy, LaSalle, Livingston	32 min
Feb 28, 6:24 PM CST	Severe Thunderstorm Warning	LOT	LaSalle	51 min
Feb 28, 6:26 PM CST	Areal Flood Advisory	LOT	Cook, Grundy, Kendall, LaSalle, Livingston, Will	3 hr
Feb 28, 6:44 PM CST	Severe Thunderstorm Warning	LOT	Kankakee, Will	46 min
Feb 28, 6:44 PM CST	Severe Thunderstorm Warning	LOT	Cook, Will	46 min
Feb 28, 7:04 PM CST	Severe Thunderstorm Warning	LOT	Grundy, Kendall, Will	41 min
Feb 28, 7:41 PM CST	Severe Thunderstorm Warning	LOT	LaSalle	34 min
Feb 28, 7:45 PM CST	Severe Thunderstorm Warning	LOT	Cook, Kankakee, Will	45 min
Feb 28, 8:04 PM CST	Severe Thunderstorm Warning	LOT	Grundy, LaSalle, Will	26 min
Feb 28, 8:24 PM CST	Special Marine Warning	LOT		96 min
Feb 28, 8:51 PM CST	Areal Flood Advisory	LOT	Cook, DeKalb, DuPage, Grundy, Kane, Kankakee and 4 more	6 hr
Feb 28, 8:57 PM CST	Severe Thunderstorm Warning	LOT	Cook, Will	37 min
Feb 28, 9:09 PM CST	Areal Flood Warning	LOT	Cook, Grundy, Kendall, Will	6 hr
Feb 28, 9:34 PM CST	Severe Thunderstorm Warning	LOT	LaSalle	56 min
Feb 28, 9:57 PM CST	Special Weather Statement	LOT	Cook	33 min
Feb 28, 10:18 PM CST	Severe Thunderstorm Warning	LOT	DeKalb, DuPage, Grundy, Kane, Kendall, Will	27 min
Feb 28, 10:56 PM CST	Special Marine Warning	LOT		64 min
Feb 28, 11:20 PM CST	Special Weather Statement	LOT	Ford, Iroquois	25 min
Feb 28, 11:27 PM CST	River Flood Warning	LOT	Lake	5 days
Feb 28, 11:28 PM CST	River Flood Warning	LOT	Cook	31 hr
Feb 28, 11:34 PM CST	River Flood Advisory	LOT	Kane, Kendall	7 days
Feb 28, 11:38 PM CST	River Flood Advisory	LOT	Cook	36 hr
Mar 1, 12:21 AM CST	River Flood Warning	LOT	Will	27 hr
Mar 1, 12:21 AM CST	River Flood Warning	LOT	Bureau, LaSalle, Putnam	72 hr
Feb 28, 6:31 PM CST	Severe Thunderstorm Warning	LOT	Lake, Porter	59 min
Feb 28, 7:31 PM CST	Severe Thunderstorm Warning	LOT	Porter	29 min
Feb 28, 11:25 PM CST	River Flood Warning	LOT	Lake	29 hr
Feb 28, 11:32 PM CST	Severe Thunderstorm Warning	LOT	Jasper, Lake, Porter	28 min
Feb 28, 11:54 PM CST	Special Weather Statement	LOT	Jasper, Newton	36 min
Mar 1, 12:04 AM CST	Severe Thunderstorm Warning	LOT	Jasper, Newton	26 min
Mar 1, 12:21 AM CST	River Flood Warning	LOT	Lake, Newton	32 hr

Nearby

Severe Thunderstorm Warnings in Illinois, 2017 Every severe thunderstorm warning 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.