Severe Thunderstorm Warning 149, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
329 PM CDT Thu Aug 3 2017

.SHORT TERM...
241 PM CDT

Through Friday...

The main concern continues to focus on the threat of strong to
severe thunderstorms late afternoon and into this evening.

Widely scattered prefrontal storms are ongoing across the area
this afternoon in response to weak capping and ascent from a
weak mid-level disturbance shifting across the area. This
activity should begin to wane from west to east for a period
within the next couple hours as this disturbance shifts east. The
severe threat with this activity will remain low due to unfavorable
deep layer shear. Skies may end up breaking up for a short period
late this afternoon, before the main round of strong to severe
thunderstorms develops and impacts the area this evening.

We are already seeing signs of renewed development over portions
of eastern Iowa in association with the surface cold front. Large
scale forcing for ascent is expected to continue to increase atop
the cold frontal boundary through the rest of the afternoon and
this evening as a stout mid-level disturbance, currently over the
Upper Midwest, digs southeastward towards the area. This should
continue to result in an uptick in thunderstorm development ahead
of the cold front as we head through the late afternoon hours. It
appears that these storms will then track eastward over northern
IL/northwestern IN this evening. Given the expected increasing
mid-level flow in association with the approaching disturbance,
deep layer shear should become strong enough to allow these
storms to have more organized structures, thus supporting a
higher severe threat this evening (~6 to 10 PM). At this time
strong damaging winds and large hail look to be the primary
threats.

Overall, this thunderstorm activity looks to remain quiet
progressive with the arrival of the surface front. For this
reason, the storms should come to a quick end from west to east
this evening. Heavy rain will be likely with these storms, but
the quick movement should lessen the threat of flooding.

Once the front pushes across the area, expect the winds to become
gusty out of the west. These gusty winds will continue on Friday.

KJB

&&

.LONG TERM...
330 PM CDT

Friday Night through Thursday...

By Friday night, the upper low and associated cold pool will lift
northeast of the region quickly this weekend with a quick
moderating trend in temperatures, though still a bit below
average. A broad, low amplitude long wave trough is forecast to
remain in place from the Northern Plains to New England into early
next week. One shortwave trough is forecast to pivot through the
base of the trough and approach the area Sunday, but models remain
somewhat inconsistent as far as timing and exact track, so timing
and coverage of associated pcpn remains a concern.

Some model variability and the tendency for widespread light QPF
in the GFS is resulting in many periods with low pops in the
blended model grids. It is hard to completely rule out precip in
this pattern, so have maintained chance PoPs into early next week.
Shortwave ridging building in aloft after Monday night should help
keep conditions dry through mid to late next week. The next
chance for pcpn may not be until Friday.

&&

.AVIATION...
For the 18Z TAFs...

The main weather concerns continue to focus on thunderstorm
timing today into this evening.

A few isolated to widely scattered thunderstorms are ongoing
across the Chicago airspace. These storms, while they may miss a
given terminal, will remain around the Chicago terminals for the
next couple hours, before shifting east of the area. Another area
of remnant thunderstorms near the Mississippi has dissipated
along its southern end over the past couple hours. However, an
associated outflow boundary remains, and is shifting eastward
into western IL at this time. Additional storms may try to begin
developing along this boundary over the next hour or two.
Confidence is not the highest with this occurring, but if it
does, it could result in another chance of storms at the terminals
around mid-afternoon.

Otherwise, the main threat of severe thunderstorms looks to be
very late this afternoon through early this evening (generally
21-00z at RFD and 23-02z at the Chicago area terminals). With this
main wave of storms this evening, expect the possibility for very
strong wind gusts and/or hail. The surface cold front should
shift across the area later this evening, bringing a quick end to
the storms. Expect winds to become westerly in the wake of the
front, with gusty west-northwesterly winds likely on Friday. A
period of lower MVFR CIGs also appears likely later tonight into
Friday morning following this frontal passage.

KJB

&&

.MARINE...
330 PM CDT

Area of low pressure over southern Wisconsin this afternoon is
expected to deepen as it lifts across Lake Michigan tonight and
will continue to deepen as it lifts towards Quebec by early
Saturday. As the low passes east of the lake, the strengthening
southeast winds will shift through southwest and strengthen
further to Gale Force by Friday morning over the southern portions
of the lake and then over the northern portions of the lake in
the afternoon. Gales should increase to 40 kt in a strong
northwest gradient into Friday night. A Gale Warning has been
hoisted for the open waters of Lake Michigan. Nearshore waters
should remain below gale force and a Small Craft Advisory has been
issued. An unseasonably cool airmass overspreading the lake Friday
will support lake effect showers and thunderstorms along with the
potential for water spouts. Winds will taper late Friday night
into Saturday as high pressure builds back across the region.
Relatively light flow should continue through the remainder of the
weekend.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Beach Hazards Statement...INZ002...10 AM Friday to 5 AM Saturday.

LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743...7 AM Friday
     to 9 PM Friday.

     Small Craft Advisory...LMZ744-LMZ745...7 AM Friday to 5 AM
     Saturday.

     Gale Warning...LMZ777-LMZ779...10 AM Friday to 3 AM Saturday.

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
356 PM CDT Thu Aug 3 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
042100-
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-
356 PM CDT Thu Aug 3 2017 /456 PM EDT Thu Aug 3 2017/

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

.DAY ONE...Tonight.

WEATHER HAZARDS EXPECTED:
  Elevated Thunderstorm Risk...with an associated:
  Limited Tornado Risk.
  Elevated Hail Risk...up to quarter size.
  Elevated Thunderstorm Wind Damage Risk...up to 70 MPH.
  Limited Flooding Risk.

DISCUSSION:

Widely scattered  to scattered thunderstorms will continue through
this evening. Storm coverage and intensity will increase through
the late afternoon into the evening hours. One general area of
thunderstorms over northeastern and east-central Illinois into
northwest Indiana will continue to push east, with chances for
marginally severe hail, strong, damaging wind gusts and heavy
downpours. Localized flooding will be possible.

Another line of storms developing just west of the Mississippi
River along a cold front will push into northwestern Illinois by
early evening and then push east across the outlook area. With
this line, the most likely hazards are damaging winds and quarter
size hail. There is a low, but non-zero, risk of a tornado as
well, should some storms develop supercell characteristics. The
thunderstorm threat will end from west to east during the late
evening hours and come to an end by around midnight tonight.

In addition, portions of the Pecatonica River will remain in
flood.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Sunday and Monday...
  Limited Thunderstorm Risk.
Wednesday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

Spotters will likely be needed this afternoon through this
evening.

GENERAL STORM MOTION OF THE DAY:

East at 30 mph.

&&

LMZ740>745-042100-
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-
356 PM CDT Thu Aug 3 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.

  Elevated Thunderstorm Risk.
  Hazardous Conditions for Small Craft are likely.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Friday...
  Hazardous Conditions for Small Craft are likely.

Sunday and Monday...
  Limited Thunderstorm Risk.

&&

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-042100-
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-
356 PM CDT Thu Aug 3 2017

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

.DAY ONE...Tonight.

Thunderstorms are likely, some could be severe through this
evening south of a Bay of Green Bay to Traverse City line.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Gales to 40 kt are likely Friday and Friday night.

There is a chance of thunderstorms and waterspouts Friday and
Friday evening.

There is also a chance of thunderstorms again Sunday and Monday
and again, Wednesday and Thursday.

&&

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Special Weather Statement
National Weather Service Chicago/Romeoville Il
335 PM CDT THU AUG 3 2017

ILZ033-INZ010-011-019-032100-
Iroquois IL-Newton IN-Jasper IN-Benton IN-
335 PM CDT THU AUG 3 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN IROQUOIS...NEWTON...
NORTHWESTERN BENTON AND SOUTHWESTERN JASPER COUNTIES UNTIL 400 PM
CDT/500 PM EDT/...

At 334 PM CDT/434 PM EDT/, Doppler radar was tracking strong
thunderstorms along a line extending from near Morocco to near
Sheldon. Movement was east at 25 mph. Additional strong thunderstorm
were located near Earl Park and Kentland and moving northeast at
about 25 mph.

Nickel size hail and wind gusts of 50 to 55 mph will be possible with
these storms.

Locations impacted include...
Rensselaer, Watseka, Kentland, Morocco, Percy Junction, Perkins,
Beaver City, Raub, Surrey, Sheldon, Goodland, Brook, Collegeville,
Beaverville, Donovan, Iroquois and Mount Ayr.

Including the following interstate...
 Indiana I-65 between mile markers 207 and 219.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4102 8710 4072 8721 4073 8772 4099 8764
TIME...MOT...LOC 2034Z 269DEG 21KT 4095 8751 4078 8762

RC

Special Weather Statement
National Weather Service Chicago/Romeoville Il
347 PM CDT THU AUG 3 2017

ILZ022-023-INZ001-002-032115-
Will IL-Kankakee IL-Porter IN-Lake IN-
347 PM CDT THU AUG 3 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN WILL...NORTHEASTERN
KANKAKEE...PORTER AND LAKE COUNTIES UNTIL 415 PM CDT...

At 347 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near New Chicago to near Lake Dalecarlia to
near Bourbonnais. Movement was east at 40 mph.

Dime to nickel size hail and winds up to 50 mph will be possible
with these storms.

Locations impacted include...
Gary, Portage, Merrillville, Valparaiso, Schererville, Hobart, Crown
Point, Griffith, St. John, Lake Station, Cedar Lake, Lowell, Manteno,
Peotone, Hebron, Lakes Of The Four Seasons, Wheeler, Boone Grove,
South Haven and Lincoln Hills.

Including the following interstates...
 I-57 between mile markers 319 and 328.
 Indiana I-65 between mile markers 239 and 258.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4134 8695 4122 8757 4120 8801 4129 8801
      4140 8761 4147 8751 4155 8742 4157 8693
      4144 8693
TIME...MOT...LOC 2047Z 269DEG 33KT 4154 8732 4136 8737 4122 8792

RC

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Special Weather Statement
National Weather Service Chicago/Romeoville Il
455 PM CDT THU AUG 3 2017

ILZ006-032215-
Lake IL-
455 PM CDT THU AUG 3 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN LAKE COUNTY UNTIL 515 PM
CDT...

At 455 PM CDT, Doppler radar was tracking a strong thunderstorm over
Lindenhurst, or over Venetian Village, moving northeast at 30 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

Locations impacted include...
Waukegan, Gurnee, Zion, Grayslake, Round Lake, Antioch, Beach Park,
Fox Lake, Lake Villa, Gages Lake, Venetian Village, Long Lake,
Pistakee Highlands, Lindenhurst, Lakemoor, Wadsworth, Volo, Third
Lake, Lake Catherine and Grandwood Park.

Including the following interstates...
 I-94 between mile markers 1 and 10.
 I-294 between mile markers 1 and 10.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4249 8780 4246 8780 4238 8781 4230 8820
      4249 8820 4250 8818 4250 8812
TIME...MOT...LOC 2155Z 241DEG 25KT 4242 8800

RC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
504 PM CDT THU AUG 03 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0455 PM     HAIL             NNW LINDENHURST         42.42N 88.03W
08/03/2017  M0.88 INCH       LAKE               IL   COCORAHS

&&

AKREIN