Areal Flood Warning 3, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
210 PM CDT Thu Aug 12 2021

.SHORT TERM...
210 PM CDT

Through Friday night...

An impressively large west to east band of thunderstorms continues
from near Manhattan, Kansas to Fowler, Indiana along the nose of a
veered by nevertheless persisent low-level jet and instability axis.
North of the complex of storms, overcast skies are prevalent which
are keeping temperatures in the upper 70s to lower 80s.

As a cold front currently stretching from southern Iowa to central
Wisconsin approaches this evening, at least widely scattered showers
and a few thunderstorms may attempt to develop along the
Illinois/Wisconsin state line. With robust moisture tranport being
effectively blocked by the aforementioned sprawling complex of
storms to our south, we feel most of the area has a much better
chance of staying dry this evening and overnight. The exception may
be across our far southern forecast area after midnight when the low-
level jet begins to ride atop whatever is left of the ongiong
convection across out south. Considering the localized 4-8 inches of
rain that fell across parts of Ford county this morning, such would
set the stage for potentially another round of flash flooding,
though confidence in this scenario is low.

Tomorrow (onward) will be beautiful with partly cloudy skies, highs
in the lower 80s, much lower humidity, and no chances for showers or
storms.

Borchardt

&&

.LONG TERM...
348 AM CDT

Friday night through Wednesday...

No significant update to extended forecast due to ongoing
convective weather overnight. Previous extended discussion remains
valid:

A shift in the longwave pattern will allow Canadian high pressure
to slowly advance along the northern CONUS, providing northerly
breezes and lowering dewpoints. High temps through the weekend
into Monday look to remain in the upper 70s to lower 80s. A
warming trend will develop on Tuesday and Wednesday as southerly
winds develop on the west side of departing high pressure. A few
showers/storms could bubble up on Tuesday afternoon and again on
Wednesday, but coverage will be isolated for the most part.

Shimon/Ratzer

&&

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

Aviation forecast concerns for this TAF period include:
-Southwest winds gusting to around 20 kts into the afternoon
-The possibility of showers and thunderstorms occurring this
 evening
-A wind shift associated with a cold frontal passage tonight and
 the potential for a wind shift occurring with a lake breeze
 tomorrow afternoon

The main focus of this TAF period, as it has been the past several
days, is the potential for showers and storms to impact the
terminals. Today looks to be the final day of this stretch of
unsettled weather within a very warm and moist air mass, though it
appears that any storms that develop near the terminals today
won't quite be as widespread or as strong as they have been the
past few days. Model soundings currently depict fairly dry air
aloft in place between a cold front to the northwest and the axis
of warm air advection-driven convection to the south. While most
model guidance initially had a line of storms firing along the
incoming cold front, the widespread convection to the south is
likely blocking some of the low-level moisture transport that
would be necessary for this to occur, and thus guidance has
trended drier in northwest Illinois near RFD during the time of
the cold frontal passage. However, a burgeoning low-level jet and
an associated northeastward theta-e surge could still foster the
development of showers and storms over the area later this
evening. Have opted to keep a TEMPO with -TSRA going in the TAFs
for now, though confidence in this actually verifying isn't all
that high.

Southwest winds will continue to gust up into the 20-25 kt range
this afternoon before subsiding with the loss of diurnal heating.
Winds will then shift to northerly behind the cold frontal passage
tonight and likely remain northerly or northwesterly across most
of the terminals through much of the day tomorrow. A lake breeze
will likely develop by tomorrow afternoon, but confidence is low
on whether it will reach MDW or ORD at the moment, so have left
any mention of a northeasterly wind shift out of these TAFs for
now. This wind shift will likely occur at GYY, but may occur at or
just after the end of the current TAF period at 18Z.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
442 AM CDT Thu Aug 12 2021

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-130945-
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-
442 AM CDT Thu Aug 12 2021 /542 AM EDT Thu Aug 12 2021/

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

.DAY ONE...Today and Tonight.

Weather hazards expected...

  Elevated Thunderstorm Risk...with an associated:
     Limited hail risk...up to quarter size here.
     Limited damaging wind risk...up to 65 mph.
  Limited Flooding Risk.
  Elevated Excessive Heat Risk.

DISCUSSION...

Scattered thunderstorms may produce isolated damaging wind gusts
south of the Interstate 80 corridor early this morning, along with
locally heavy rainfall and possibly some flooding. Additional
scattered thunderstorms are possible late this afternoon into
tonight across the entire area. Some of these storms may be
severe, with damaging wind gusts the main threat, with the severe
threat decreasing late evening into the overnight.

Warm and humid conditions will persist today, though peak
afternoon heat indices should top out just under 105 degrees.

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

Friday...
  Limited Thunderstorm Risk.
Tuesday and Wednesday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotters may be needed late this afternoon and this evening.

GENERAL STORM MOTION OF THE DAY:

  Moving toward east at 35 mph early this morning, and to the
  southeast at 35 mph later today and tonight.

LMZ740>745-130945-
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-
442 AM CDT Thu Aug 12 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...Today and Tonight.

Weather hazards expected...

  Elevated Thunderstorm Risk...with an associated:
     Limited Waterspout Risk.
     Limited hail risk...up to quarter size.
     Limited thunderstorm wind gust risk...up to 55 knots.

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

Friday...
  Limited Thunderstorm Risk.
Wednesday...
  Limited Thunderstorm Risk.

Ratzer

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
1252 PM CDT THU AUG 12 2021

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

1251 PM     FLASH FLOOD      1 S GIBSON CITY         40.46N 88.38W
08/12/2021                   FORD               IL   EMERGENCY MNGR

            SIGNIFICANT FLASH FLOODING OCCURRING IN AND
            AROUND GIBSON CITY, AND POINTS SOUTH AND
            WEST. WATER IS INUNDATING HOMES AND
            BUSINESSES, SEWERS ARE BACKING UP, AND ALL
            ROADS ARE IMPASSABLE. NUMEROUS WATER RESCUES
            CONTINUE.

&&

BB

Special Weather Statement
National Weather Service Chicago/Romeoville
109 PM CDT Thu Aug 12 2021

ILZ033-039-121900-
Iroquois IL-Ford IL-
109 PM CDT Thu Aug 12 2021

...A strong thunderstorm will impact portions of southeastern Ford
and southern Iroquois Counties through 200 PM CDT...

At 108 PM CDT, Doppler radar was tracking a strong thunderstorm over
Paxton, moving east at 45 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Paxton, Loda, Wellington and Clarence.

Including the following interstate...
 I-57 between mile markers 258 and 268.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

&&

LAT...LON 4054 8825 4058 8753 4049 8753 4049 8794
      4040 8793 4040 8827
TIME...MOT...LOC 1808Z 268DEG 41KT 4044 8814

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

Carlaw

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
139 PM CDT THU AUG 12 2021

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

0130 PM     HEAVY RAIN       GIBSON CITY             40.47N 88.37W
08/12/2021  M8.76 INCH       FORD               IL   PUBLIC

            PRIVATE WEATHER STATION REPORTS 8.76 INCHES
            OF RAINFALL SINCE MIDNIGHT. 8.1 INCHES
            OCCURRED WITH MOST RECENT STORMS WHICH BEGAN
            AT 8:30 AM. MULTIPLE 1 HOUR PERIODS WITH
            OVER 2 INCHES OF RAINFALL. LIGHT RAIN
            ONGOING.

&&

WSL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
141 PM CDT THU AUG 12 2021

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

0130 PM     HEAVY RAIN       4 WNW GIBSON CITY       40.48N 88.45W
08/12/2021  M6.74 INCH       FORD               IL   PUBLIC

            PRIVATE WEATHER STATION REPORTS 6.74 INCHES
            SINCE MIDNIGHT. 5.89 INCHES OCCURRED WITH
            MOST RECENT STORMS SINCE 8 AM. LIGHT RAIN
            ONGOING.

&&

WSL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
216 PM CDT THU AUG 12 2021

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

0214 PM     FLASH FLOOD      1 SE GIBSON CITY        40.46N 88.37W
08/12/2021                   FORD               IL   EMERGENCY MNGR

            WATER RESCUES CONTINUE AT A SENIOR CITIZENS
            CENTER THAT WAS INUNDATED WITH WATER. MOST
            ROADWAYS REMAIN IMPASSABLE.

&&

BB

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