Severe Thunderstorm Warning 113, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
326 AM CDT Sat Jun 6 2026

.KEY MESSAGES...

- Shower and thunderstorm threat this afternoon-evening will
  focus primarily south of I-80, though showers and a few storms
  will also be possible near the lake breeze pushing inland.

- While there will be daily shower and thunderstorm chances
  through the upcoming week, expect plenty of dry hours. Outside
  of the convective chances, it will be very warm and humid
  (focused away from the lake until Tuesday).

&&

.DISCUSSION...
Issued at 326 AM CDT Sat Jun 6 2026

Early This Morning:

Scattered thunderstorm development overhead in the pre-dawn
hours (as of this writing) is associated with convectively
modulated impulses and a glancing blow from a stronger short-
wave pushing into the northern Lakes. It's unclear to what
extent additional upstream convection from western WI to
western/west central IL will push into the area over the next
few hours. We'll need to continue to monitor for a few strong
to potentially severe storms (wind and hail threat) given fairly
steep mid-level lapse rates and 30-40 kt of effective bulk shear.

Today through Sunday:

In the wake of the early morning convection, aside from a few
lingering isolated to widely scattered storms south of I-80,
conditions should dry out areawide for a time. Fairly strong
mid-level subsidence and drying, particularly north of I-80,
casts doubt on much in the way of renewed PM thunderstorm
development with northward extent in the CWA. The possible
exception will be near a lake breeze boundary as it pushes
inland across the Chicago metro this afternoon. Farther south,
primarily south of I-80 (possibly well south), uncapped,
moderately to strongly unstable air mass should yield corridors
of scattered "airmass" type thunderstorms. With mid-level lapse
rates decreasing to 6C/km or less and deep layer shear down to
25 kt or less, overall severe threat appears limited, likely
relegated to localized strong to perhaps severe downburst winds.
If a corridor of robust convection is able to persist into or
through the evening despite modest at best forcing, high PWATs
and high freezing levels could support localized flooding
(albeit in our typically less flood prone southern areas).

Given expectation of increasing sunshine this afternoon,
especially with northward extent, look for highs inland of the
lake breeze in the mid to upper 80s amidst dew points in the 60s
to around 70F. Near the lake, highs will reach the mid 70s to
around 80F ahead of the lake breeze and then slowly but steadily
fall thereafter.

After festering evening storms primarily south of I-80 erode
diurnally, there should be a relative lull overnight into
Sunday. The lake shadow will extend farther inland on Sunday,
confining isolated to widely scattered pulse airmass convection
at peak heating to the southwestern 1/3 to 1/2 or so of the
CWA. Sub- marginal wind shear and lapse rates suggest severe
weather is unlikely. Highs will reach the lower to mid 80s
inland, but only upper 60s to lower 70s near the lake.

Sunday Night Onward:

Weakening mid-upper low/short-wave will shear out on Sunday
night into Monday as it encounters robust ridging centered over
the eastern Lakes by then. Nonetheless, weakly capped tropics-
like airmass should support fairly widespread showers and at
least scattered storms developing as early as midday Monday
(unless debris cloudiness proves too detrimental to sufficient
destabilization). Southeasterly synoptic flow and lake breeze
reinforcement will keep IL shoreline locations in the 70s on
Monday, while the rest of the area reaches the low-mid 80s.

Looking ahead at the rest of next workweek, there have been some
guidance members with sufficiently strong mid-level ridging and
low-level thermal ridging poking into the Great Lakes region for
a few days of very warm (locally hot) and humid conditions. With
that said, the more likely scenario is our area being on the
precarious northwestern periphery of ridging centered near the
East Coast. This should entail less capping and a continuation
of shower and thunderstorm chances. By later in the week
(Thursday or thereabouts), seasonably strong troughing from the
north central US to central Canada could plausibly yield a
pattern supportive of organized strong to severe convection into
the region.

Note that the NBM depicted temperatures centered Tuesday through
Friday (most notably on Wednesday and Thursday) are well
outside of the ensemble spectrum due to likely spurious upward
bias correction. Thus we will withhold from any heat messaging
locally. It looks to be very warm and humid, but not hazardously
so, per the current global ensemble guidance consensus.

Castro

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1153 PM CDT Fri Jun 5 2026

Forecast concerns include...

Scattered thunderstorms overnight.
Chance of showers and isolated thunderstorms Saturday afternoon.
Wind shift/lake breeze Saturday afternoon.

A slowly weakening line of thunderstorms across southern WI will
continue moving south along with an outflow boundary, which is
expected to move into northern IL in the next hour or so and
allow current isolated thunderstorms to expand in coverage and
move southeast across the terminals during the early morning
hours. Only medium confidence for coverage with increasing
confidence for timing and have adjusted tempo timing to 06z-10z
but timing may only be a few hours at any one location. There
could be lingering showers, perhaps an isolated thunderstorm
through daybreak, as the activity weakens and moves southeast of
the terminals.

A lake breeze is expected to move inland Saturday afternoon,
shifting winds easterly for the Chicago terminals. There is a
low chance for showers and possibly a few thunderstorms to
develop along the lake breeze, especially across northwest IN,
as it moves inland. Despite low confidence, opted to include
prob shower mention for a few hours for this potential. Trends
may eventually support the need for prob thunder mention with
later forecasts.

Southwest winds overnight will turn more westerly later Saturday
morning, possibly northwest Saturday afternoon, before shifting
easterly behind the lake breeze. Winds are expected to become
easterly across most of the area Saturday evening. cms

&&

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

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
418 AM CDT Sat Jun 6 2026

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-070930-
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-
418 AM CDT Sat Jun 6 2026 /518 AM EDT Sat Jun 6 2026/

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

.DAY ONE...Today and Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk...with an associated:
     Level 1 of 5 Damaging Wind Risk...up to 50 to 60 mph.
     Limited Flooding Risk.

DISCUSSION...

This afternoon into this evening, renewed thunderstorm development
will likely focus primarily south of I-80, where a few storms may
be capable of producing localized strong winds and flooding.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Sunday through Friday...
  Limited Thunderstorm and associated Flooding Risk at times.

DISCUSSION...

The weather pattern will continue to feature seasonably warm and
humid conditions through next week, with periodic shower and
thunderstorm chances. Some of the storms will be capable of
producing torrential downpours, which may lead to localized
flooding.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation is unlikely today.

GENERAL STORM MOTION OF THE DAY:

 Moving toward the east-southeast at 20 to 30 mph.

LMZ740>745-070930-
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-
418 AM CDT Sat Jun 6 2026

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...

  Limited Thunderstorm Risk.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Sunday through Friday...
  Limited Thunderstorm Risk at times.

Castro

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