036
FXUS63 KLOT 060453
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1153 PM CDT Fri Jun 5 2026

.KEY MESSAGES...

- Waves of showers and storms are expected to continue into
  early next week. Many hours will be dry.

- Scattered to numerous storms are likely to occur in the area
  overnight into Saturday morning. The strongest storms tonight
  may be severe and produce torrential downpours.

- Near to slightly above average temperatures are expected this
  weekend before trending warmer next week.

&&

.UPDATE...
Issued at 805 PM CDT Fri Jun 5 2026

Have made some adjustments to the near-term portion of the
forecast through midnight tonight, primarily to lower pops
significantly and raise temps a smidge.

Regional radar imagery indicates rain/showers which affected
the area earlier today has shifted east into lower Michigan in
association with a mid-level short wave and an embedded remnant
MCV. Weak subsidence in the wake of those features has yielded
relatively quiet weather conditions across the forecast area
early this evening, outside of some spotty isolated light
showers mainly north of the I-80 corridor within a region of
weakly confluent low-level flow and modest but persistent
warm/moist advection on southwest 925- 850 mb flow aloft. Some
individual CAM runs have been fairly bullish with igniting
convection across this area this evening, though WoFS runs and
current satellite trends argue against significant development
in the near term.

We do continue to monitor a couple of areas upstream of the cwa
however for an expected increase in shower/thunderstorm
coverage. The first is the westward extent of the aforementioned
low-level confluent zone which can be seen as an area of
slightly agitated cumulus clouds from northwest of the Quad
Cities back through southeastern Nebraska (where thunderstorms
have initiated since late this afternoon). The other to our
north across central and northeast Wisconsin, where a linear
convective line has developed and is propagating to the
southeast. High-res guidance has been rather consistent in
developing thunderstorms eastward in the vicinity of the
confluent zone across southern Iowa near the Missouri border and
eventually into norther/central Illinois overnight, while the
Wisconsin storms continue to track southeast (likely in a
weakening form but with an outflow boundary potentially
maintaining enough forcing for convection to persist into parts
of our cwa). Given otherwise warm, humid boundary layer
conditions, some of these storms may pose a localized wind or
hail threat after midnight tonight.

With the above scenario in mind, had lowered pops through the
evening hours considerably (limited to slight chance or less
than 25 percent), blending into our going higher chance/likely
pops after midnight. Have also raised hourly temps and overnight
mins a bit, with readings expected to be somewhat slow to cool
off with our higher dew points and light southwest surface
winds.

Ratzer

&&

.DISCUSSION...
Issued at 409 PM CDT Fri Jun 5 2026

Through Sunday:

Extensive cloud cover this morning and afternoon prevented
enough destabilization from occurring to support much of a
thunderstorm threat from materializing today, even as a well-
defined MCV passed close by. The bulk of the shower activity
associated with the MCV will continue to peel away to the east
over the next hour, leaving most of our area dry for the
remainder of the afternoon and evening, though the soupy air
mass will still likely support isolated showers lingering
through much of this time frame. Still couldn`t rule out some
lightning occurring during this time frame as well, especially
since equilibrium levels will rise and mid-level lapse rates
will steepen going into this evening as a remnant EML plume is
advected into the area from the west. That said, with forcing
support diminishing with the departure of the MCV, confidence in
lightning occurring through this evening is not particularly
high.

Later tonight, increasing isentropic lift induced by a
strengthening low-level jet will attempt to activate the EML
plume, with ascent likely to be focused near and along a
modified composite outflow boundary that will extend from near
the I-80 corridor in our CWA back westward into southern
Nebraska and northern Kansas. Aided by favorable jet dynamics
aloft, convection is first expected to initiate along this
boundary in the central Plains this evening before spreading
eastward. Between eastward-surging cold pools driving this
convection towards and potentially into our area after midnight
and new cells popping near the surface boundary later on in the
night farther to the east, at least scattered thunderstorms
appear likely occur in our forecast area overnight.

CAM guidance continues to favor the greatest convective
coverage near and south of I-80, which makes sense given the
expected storm motions and initial positioning of the surface
boundary, so have introduced likely PoPs for these areas. That
said, in a true moisture-laden summertime air mass with plenty
of instability aloft like this one, anywhere will ultimately be
fair game for convection to occur, so have kept mid-range
chance PoPs going outside of this more favored corridor for
convection. In addition, another upper-level shortwave trough
tracking through the Upper Midwest could yield a loosely-
organized convective complex that tracks across Wisconsin
tonight. Outflow associated with this complex may tend to
propagate southward and could end up entering northern Illinois
at some point late tonight or early tomorrow morning. If that
does end up occurring, then this outflow boundary could serve as
a focus for convection in our northern locales independent of
what happens farther to the south.

The steeper mid-level lapse rates on the order of 7-7.5 C/km
paired with the existing rich low-level moisture will yield
around 2000-3000 J/kg of MUCAPE across much of our forecast area
well into the night. Deep-layer shear values could vary
considerably with location and time, depending on how far south
the mid-level jet over the Upper Midwest dips and how quickly,
so a messy mix of storm modes is possible. Regardless of the
exact storm mode though, the aforementioned thermodynamic
parameters should support some potential for locally strong to
damaging winds and hail with the more robust convection.
Precipitable water values between 1.25 and 1.75 inches will also
result in torrential rainfall, and the somewhat parallel
orientation of the low-level jet and isentropic forcing with
respect to the aforementioned outflow boundary (or boundaries)
does lend some concern for training convection and localized
flash flooding. That said, the recent dry conditions may tend
to limit this potential to our usual more flood-prone areas.

Any convection that lingers after daybreak on Saturday should
diminish over the course of the morning as the low-level jet
weakens with time. Away from any residual morning cloud cover
and a lake breeze that will push inland, temperatures should
warm solidly into the 80s. The upper 60s-low 70s dew points and
associated instability will hang around for another day, leading
to muggy conditions that could support additional thunderstorm
development later on in the day. A relative lack of large-scale
forcing mechanisms may tend to keep thunderstorm coverage
somewhat limited tomorrow with most locations in our CWA favored
to remain dry, but surface convergence along the lake breeze and
any residual outflow boundaries from the overnight convection
may still prove to be enough for diurnal thunderstorms to fire
in a few areas. MLCAPE approaching 3000 J/kg amidst lackluster
deep-layer shear could support the potential for isolated
strong to damaging wet downbursts with the strongest storms
tomorrow afternoon.

Ogorek


Sunday into Monday:

Toward the start of next week, the upper-level low currently
traversing the US/Mexican border will finally begin lifting
northeastward toward the Mississippi River Valley. The (by this
point somewhat stagnant) humid airmass will hence be poised to
support episodes of showers and storms as the upper-level low
approaches and eventually moves overhead. Periods of cloud
cover, as well as onshore flow forced by a surface high pressure
system moving across eastern Canada, will lead to seasonable
temperatures generally close to 80 degrees both days.


Tuesday Onward:

In the wake of the upper-level low, ensemble model guidance
appears steadfast in depicting the development of persistent
troughing across the Pacific Coast and upper-level ridging
across the Midwest and Great Lakes region. As a result,
temperatures should warm throughout next week with highs
climbing into upper 80s to perhaps lower 90s by the weekend.
When combined with the continued humidity, it`ll start to feel
more like summer next week. Will note that there are differences
in the placement of the ridge next week, suggesting that there
may be opportunities for storms (and associated localized
natural air conditioning) in the general region as well.

(Note that the high temperatures in the mid to upper 90s and
associated much higher heat indices being advertised by the NBM
toward the end of next week are not currently supported by input
ensemble data).

Borchardt

&&

.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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