Special Weather Statement, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
648 PM CDT Mon Jun 28 2021

.SHORT TERM...
305 PM CDT

Through Tuesday...

Waves of showers and thunderstorms will continue to be the focus through
at least midday Wednesday. Southwesterly flow around the
periphery of a broad ridge over the eastern third of the country
and an upper trough over the northern Plains continues to be
favorable. The first wave of showers and thunderstorms is crossing
the area now with a bit of a break behind it before another area
of storms moving northeast from west/central IL arrives yet this
evening. With additional shortwaves tracking through the flow
through later Tuesday. May see some decrease in coverage as some
of this is likely diurnally influenced. Coverage will likely not
be solid but many areas will likely see repeated instances of
thunderstorms through late Tuesday. With precipitable water values
pushing 2 inches and the potential for repeat storms, though not
necessarily training in the typical sense, will maintain the Flash
Flood Watch for the area. Have seen intense rainfall rates play
out again this afternoon with 1 inch+ per hour rates in spots.

The northern plains trough is expected to be kicked eastward
Tuesday night which will push a cool front southward into
Wednesday. A reinforcing trough will push south across Hudson Bay
which will drive the front towards the Ohio River Valley into
Thursday morning. Until then, the front looks to make slow
progress across the forecast area into Wednesday. Will likely have
some severe potential later Tuesday with any thunderstorms as a
surface low passes to the northwest of the local area. By
Wednesday, the flow will be oriented more west to east which will
allow for more of a west to east orientation of shower and
thunderstorm movement. This will keep heavy rain/flooding concerns
going through Wednesday, especially for central and southern
portions of the area. The Wednesday time period is further
discussed below...

MDB

&&

.LONG TERM...
310 PM CDT

Thinking of previous long term discussion remains valid and it
follows below...

Tuesday Night through Sunday...

Forecast focus in the extended period continues to be on shower
and thunderstorm trends through mid-week, then shifts to the
arrival of drier and cooler conditions for the end of the week.
Global guidance continues to trend slightly farther east with an
upper trough over the holiday weekend, offering hope for mainly
dry weather during that time.

The blocky upper level pattern that we've seen over the past several
days is expected to persist into mid-week, before a gradual
weakening of upper level ridging centered off the mid-Atlantic coast
allows our upper Midwestern trough to shift eastward. Prior to this
shift, southwesterly flow will maintain a plume of deep moisture
from the western Gulf into the Great Lakes region characterized by
juicy PWATs around 2 inches. As the upper trough begins to shift
east Tuesday night into Wednesday, surface low pressure will track
across the northern Lakes and will trail a cold front slowly
southeastward across the forecast area. Low level convergence ahead
of the front, combined with increasing large scale forcing
associated with height falls ahead of the upper trough will likely
serve to maintain the threat of additional clusters of potentially
heavy-rain producing thunderstorms. Flow aloft also increases along
the southern periphery of the upper level jet streak ahead of the
upper trough, which may support storm organization and some severe
gusty wind threat Tuesday evening, and perhaps again Wednesday
afternoon/evening across mainly the south/southeastern part of the
cwa as the front completes it's slow transit of the forecast area.

By Thursday, the cold front will be moving south of the forecast
area, though some scattered shower/thunderstorm potential may linger
linger as the upper level trough axis moves across the area and
cooler mid-level temps maintain some instability. Medium range
ensemble guidance has continued to trend toward the ECMWF/EPS
forecast of shifting the upper trough axis to the east/southeast of
the forecast area Thursday night into Friday, which would suggest a
drier trend into the weekend. There still remains some spread with
just how far east the trough axis (and potentially a closed upper
low) get however - the 00Z operational GFS has a closed H5 low over
IL at 18Z Saturday - so uncertainty still exists. Blended NBM pops
have decreased for the Friday-Sunday period though still exhibit
slight chances mainly during the afternoon hours for the possibility
of diurnally-driven instability shower and that seems appropriate
given the lingering spread. Hopefully things will continue to trend
toward the farther east/drier ECMWF/EPS solutions which would
support a mainly dry holiday weekend.

Warm and humid conditions will persist into Wednesday, before cooler
weather spreads in behind the front on northerly low level flow
Thursday and Friday. After muggy highs in the lower 80s Wednesday,
temps by Friday are only expected to be in the low-mid 70s with
modest lake cooling as well. If the upper trough does shift farther
east over the weekend, temps would likely gradually moderate back to
around average (low 80s) by Sunday.

Ratzer

&&

.AVIATION...
For the 00Z TAFs...

The pattern across the region continues to favor periods of TS
through the forecast window, though there are some favored
timeframes for potential TS. Isolated TS currently developing
southwest of the Chicago metro are expected to drift NE across the
terminals through mid-evening, with most activity either exiting
the area or dissipating by 03Z. Dry/VFR conditions are then
expected through the remainder of the night amid light SW winds.

A weak area of WAA may result in a northward-moving band of
scattered elevated TS passing over the terminals after daybreak
Tuesday, but confidence remains low enough to maintain a PROB30 at
this time. During this period, low-end MVFR ceilings may develop
and continue into the late morning.

Then, a low to mid-level trough will likely produce an area of
scattered TS across northern Illinois and northwest Indiana early
to mid-afternoon. Any of these TS will be capable of very heavy
rain rates and wind gusts possibly over 30 knots. Behind this area
of TS, dry conditions should once again prevail for Tuesday
evening.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
     ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108
     until 7 PM Tuesday.

IN...Flash Flood Watch...INZ001-INZ002-INZ010-INZ011-INZ019 until 7
     PM Tuesday.

LM...None.
&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
454 PM CDT Mon Jun 28 2021

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-292200-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
454 PM CDT Mon Jun 28 2021 /554 PM EDT Mon Jun 28 2021/

This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk...with an associated:
     Limited damaging wind risk...up to 60 mph.
  Limited Flooding Risk.

DISCUSSION...

 Additional rounds of scattered thunderstorms with torrential
 downpours and gusty winds are expected this evening. Flooding of
 ditches, farm fields, and roadways may occur beneath the
 strongest storms, especially in areas that already received
 rainfall today. A Flash Flood Watch remains in effect for
 northern Illinois and northwestern Indiana until Tuesday
 evening.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  Limited Severe Thunderstorm Risk.
  Limited Flooding Risk.
Wednesday...
  Limited Flooding Risk.
  Limited Thunderstorm Risk.
Thursday and Friday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotters activation is not anticipated, though rainfall and
  flooding reports would be appreciated.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the northeast around 20 mph.

LMZ740>745-292200-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
454 PM CDT Mon Jun 28 2021

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk...with an associated:
   Limited thunderstorm wind gust risk...up to 40 kt.
  Limited Fog Risk.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  Limited Severe Thunderstorm Risk.
Wednesday and Thursday...
  Limited Thunderstorm Risk.

Lenning

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Special Weather Statement
National Weather Service Chicago/Romeoville
230 PM CDT Mon Jun 28 2021

ILZ013-104-105-282000-
Southern Cook IL-DuPage IL-Central Cook IL-
230 PM CDT Mon Jun 28 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN DUPAGE AND SOUTH
CENTRAL COOK COUNTIES UNTIL 300 PM CDT...

At 230 PM CDT, Doppler radar was tracking a strong thunderstorm over
Homer Glen, moving east northeast at 30 mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
Bolingbrook, Orland Park, Tinley Park, Downers Grove, Woodridge, Oak
Forest, Homer Glen, Palos Hills, Lemont, Justice, Burr Ridge, Darien,
Bridgeview, Hickory Hills, Palos Heights, Worth, Willowbrook,
Countryside, Willow Springs and Indian Head Park.

Including the following interstates...
 I-55 between mile markers 270 and 281.
 I-57 near mile marker 344.
 I-80 between mile markers 150 and 151.
 I-355 between mile markers 8 and 10, and mile marker 12 and near
mile marker 15.

This includes...  Argonne National Laboratory, Hollywood Casino
Amphitheatre, and Moraine Valley Community College.

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.

&&

LAT...LON 4155 8774 4154 8779 4156 8779 4156 8791
      4164 8791 4164 8803 4173 8803 4173 8807
      4174 8807 4178 8783
TIME...MOT...LOC 1930Z 247DEG 25KT 4161 8798

Birk

SPECIAL WEATHER STATEMENT
National Weather Service Chicago/Romeoville IL
238 PM CDT Mon Jun 28 2021

ILZ003-004-008-010-011-282145-
Winnebago-Boone-Ogle-Lee-De Kalb-
Including the cities of Rockford, Belvidere, Rochelle, Oregon,
Byron, Dixon, DeKalb, and Sycamore
238 PM CDT Mon Jun 28 2021

...Funnel Clouds Possible Next Few Hours...

Conditions are favorable for the development of funnel clouds in
conjunction with isolated showers and thunderstorms mainly west
of Interstate 39. The chance for these funnel clouds to make
contact with the ground is low. Seek shelter as these isolated
thunderstorms approach.

Special Weather Statement
National Weather Service Chicago/Romeoville
809 PM CDT Mon Jun 28 2021

ILZ005-006-012-103-290145-
Lake IL-Kane IL-McHenry IL-Northern Cook IL-
809 PM CDT Mon Jun 28 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN LAKE...NORTHEASTERN
KANE...SOUTHEASTERN MCHENRY AND NORTHWESTERN COOK COUNTIES UNTIL 845
PM CDT...

At 809 PM CDT, Doppler radar was tracking a strong thunderstorm over
northern Kane County, moving northeast at 30 mph.

Winds in excess of 45 mph will be possible with this storm.
Torrential rainfall is also occurring with this storm.

Locations impacted include...
Elgin, Hoffman Estates, Crystal Lake, Carpentersville, Algonquin,
Lake in the Hills, McHenry, Huntley, Lake Zurich, Wauconda,
Barrington, Island Lake, Cary, Pingree Grove, Gilberts, Long Grove,
Hawthorn Woods, Inverness, West Dundee and Hampshire.

Including the following interstate...
 I-90 between mile markers 44 and 56.

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 4199 8842 4210 8854 4240 8821 4219 8799
TIME...MOT...LOC 0106Z 228DEG 25KT 4210 8838

Kluber