Tornado Warning 30, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
643 PM CDT Mon Jul 15 2024

.KEY MESSAGES...

- Strong to severe thunderstorms expected late this afternoon
  into tonight. Locally heavy rainfall possible, which could
  lead to additional flooding.

- Additional thunderstorm chances continue Tuesday, mainly
  south of I-80/east of I-55.

- Pattern breaks by Wednesday, with dry weather and seasonable
  temperature and humidity through the weekend.

&&

.MESOSCALE...
Issued at 546 PM CDT Mon Jul 15 2024

Explosive severe thunderstorm development has taken place across
Iowa, with storm tops exceeding 65kft. Special soundings from
DVN and ILX both show extreme instability and moderate deep
layer shear, though sufficient shear to support storm scale
organization in light of the extreme instability.

Already seeing signs of amalgamating cold pools/downdrafts with
convection over Iowa with radar showing some developing rear
inflow jets. The evolution of the convection so far continues to
fit the expectations for today with evolution to QLCS well
underway. As cold pool strengthens, would anticipate a QLCS to
begin accelerating eastward with increasing damaging wind threat
as storms approach and cross the Mississippi River.

Strengthening low level jet this evening over northern Illinois
should result in a ramping up of low level shear and coincident
increasing threat of QLCS tornadoes with bowing segments and/or
line embedded supercells. Given the shear/instability combo,
threat is certainly there for a large number of QLCS tornadoes
this evening over northern IL.

Recent satellite/radar imagery shows some cells developing over
far northern Winnebago County near the Wisconsin line. This
could be the beginnings of a "warm air advection" wind ahead of
the Iowa QLCS, which if it is and continues to fill in this
could result in a potential significant/high end flash flood
threat in our CWA if storms drift south of the IL/WI border.
Given the vulnerability of the Rockford area due to nearly 10"
of rain over the past 48 hours, this will be something that we
will be monitoring extremely closely.

- Izzi

&&

.DISCUSSION...
Issued at 247 PM CDT Mon Jul 15 2024

Through Tuesday Night:

Showers and storms may linger into the morning hours, especially
across the southern portion of the CWA. There is a chance that
the cold front associated with the storms may set up in a west
to east fashion and stall out across the southern portion of the
area, which could lead to storms persisting into the evening
over this area. However, most of the 12Z CAMs show this scenario
playing out south of the area. Although the chances of this
seem to be on the lower side, did include chance PoPs across the
southern CWA through Tuesday afternoon to account for this
possibility.

With the cold front moving through the area, Tuesday will be
cooler than today with temperatures in the mid-to-upper 80s.
Dew points will still be around 70 degrees, so it may still feel
a bit on the humid side, but peak heat indices will only be in
the 90-95 degree range.

Carothers

Wednesday through Monday:

The main upper trough axis is expected to shift east across the
forecast area Wednesday. Despite steep low-level lapse rates
depicted in forecast soundings, warm mid-level temps (700-600
mb) look to provide a capping inversion with respect to surface
based convective development. Therefore, forecast for Wednesday
is dry at this point. Broad surface high pressure then builds
across the area through the end of the week, setting the stage
for a well-deserved period of dry and seasonably mild but less-
humid weather conditions, downstream of a high-amplitude upper
ridge which develops over western North America.

Ratzer

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued by National Weather Service Gaylord, MI
643 PM CDT Mon Jul 15 2024

The primary aviation weather concerns for the 18Z TAF period include:

* Severe squall line this evening

* Period of MVFR ceilings (at least?) ahead of and behind a cold
  front expected to pass through in the 12z-18z time frame.

QLCS has developed as expected and pressing across the Mississippi
River as of this writing.  Storms expected to reach KRFD around 01z
and into the Chicago metro in the 02-03z time frame with strong wind
gusts in excess of 40 knots anticipated.  Still looks to be a period
of MVFR ceilings in the wake of this evening's convection into
Tuesday morning though flight conditions are expected to improve
toward midday with a wind shift to the northwest behind a cold front
(and likely a lake breeze impacting KORD/KMDW during the afternoon).

JPB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until 3 AM CDT Tuesday for ILZ003-ILZ004-ILZ005-
     ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-
     ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-
     ILZ106-ILZ107-ILZ108.

     Heat Advisory until 7 PM CDT this evening for ILZ008-ILZ010-
     ILZ011-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ106-ILZ107-ILZ108.

IN...Flood Watch until 3 AM CDT /4 AM EDT/ Tuesday for INZ001-
     INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
342 PM CDT Mon Jul 15 2024

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-162045-
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-
342 PM CDT Mon Jul 15 2024 /442 PM EDT Mon Jul 15 2024/

This Hazardous Weather Outlook is for portions of north central
Illinois...northeast Illinois and northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Significant Thunderstorm Risk...with an associated:
     Level 3 of 5 Tornado Risk.
     Level 4 of 5 Damaging Wind Risk...up to 80 mph.
     Level 1 of 5 Hail Risk...up to quarter size.
     Level 3 of 4 Flash Flooding Risk.

DISCUSSION...

Strong to severe thunderstorms are expected to move across the
area this evening. Damaging winds and tornadoes are expected to
be the primary severe hazards. In addition, thunderstorms will
produce torrential rainfall which will likely result in flash
flooding, possibly significant in a few areas.

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

Tuesday...
  Limited Thunderstorm Risk mainly south of I-80.

DISCUSSION...

Scattered thunderstorms are possible again on Tuesday afternoon,
primarily near and south of I-80.

.SPOTTER INFORMATION STATEMENT...

  Spotters will likely be needed this afternoon and evening.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east-southeast at 40 to 45 mph.

LMZ740>745-162045-
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-
342 PM CDT Mon Jul 15 2024

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...

  Significant Thunderstorm Risk...with an associated:
     Level 3 of 5 Thunderstorm Waterspout Risk
     Level 4 of 5 Thunderstorm Wind Gust Risk...up to 70 knots.
     Level 1 of 5 Hail Risk...up to quarter size.

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

Tuesday...
  Limited Thunderstorm Risk mainly risk southeast of Chicago.

Carothers

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Preliminary Local Storm Report
National Weather Service Chicago IL
901 PM CDT Mon Jul 15 2024

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

0828 PM     Tstm Wnd Gst     2 NW Sycamore           42.02N 88.71W
07/15/2024  M58 MPH          De Kalb            IL   Mesonet

&&

sb

Preliminary Local Storm Report
National Weather Service Chicago IL
902 PM CDT Mon Jul 15 2024

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

0832 PM     Tstm Wnd Gst     3 N Sycamore            42.04N 88.68W
07/15/2024  M60 MPH          De Kalb            IL   Mesonet

&&

sb

Preliminary Local Storm Report
National Weather Service Chicago IL
907 PM CDT Mon Jul 15 2024

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

0857 PM     Tstm Wnd Gst     2 WNW Sugar Grove       41.77N 88.48W
07/15/2024  M70 MPH          Kane               IL   ASOS

            ASOS measured 61 kt gust at Aurora Municipal
            Airport (KARR).

&&

Ratzer