Downers Grove, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

969
FXUS63 KLOT 092339
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
639 PM CDT Mon Jun 9 2025

.KEY MESSAGES...

- Dry conditions are expected tonight through Wednesday, along
  with warming temperatures.

- Shower and thunderstorm chances return Wednesday night and
  last through at least the weekend.

- There is an emerging signal for hot and humid conditions to
  develop across the general region next week.

&&

.DISCUSSION...
Issued at 312 PM CDT Mon Jun 9 2025

Through Tuesday night:

While an isolated thunderstorm did develop over Lake County, IL
earlier before moving out over the lake, the surface cold front
pushed through just a little too quickly for a more appreciable
coverage of thunderstorms to be realized here, instead causing
more widespread thunderstorm development to occur just to our
east in northern Indiana and southwest Michigan. We`ll still
have to keep an eye on the more agitated cumulus along and just
behind the cold front in northwest Indiana over the next hour or
two for any signs of deeper convective development, but the
already low thunderstorm chances otherwise appear to be quickly
dwindling. Isolated showers should still occur in northwest
Indiana over the next one to two hours, and some spotty light
showers closer to the core of the upper-level low over the
region could sneak just south of the Wisconsin state line prior
to fizzling closer to sunset, but otherwise, the remainder of
the forecast area should remain dry into tonight.

Dry conditions will then continue to prevail through Tuesday
night as the upper-level trough departs to our northeast and
the axis of a surface ridge slowly slides eastward across our
longitude. The main sensible weather item of note tomorrow looks
to be Canadian wildfire smoke yet again as northwesterly flow
on the backside of the departing trough funnels another coherent
plume of it in our direction. Upstream ASOS/AWOS observations
in the eastern Dakotas show that some of this smoke is at
ground-level, and the latest HRRR and RAP smoke models indicate
that some near-surface smoke could be observed again here
tomorrow as this smoke advects our way. The highest near-
surface smoke concentrations are depicted during the afternoon
as the top of the boundary layer expands into the 1 to 2 km AGL
layer, where the greatest smoke concentrations will reside.

It should be said, though, that both the HRRR and RAP smoke
models were a bit overzealous with mixing higher smoke
concentrations down to the surface on multiple occasions during
our recent bouts of wildfire smoke, so confidence in their
latest near-surface output isn`t particularly high at this
time. Alongside our neighboring WFOs, have thus elected to hold
off on introducing a formal smoke mention in the weather grids
for now. However, we`ll need to monitor upstream observations
closely tonight into tomorrow as the introduction of such a
mention may eventually be needed. Did keep our sky cover
percentages higher than they otherwise would be tomorrow with
the expectation that skies should be quite hazy again from the
smoke, though. The filtered sunshine should still nevertheless
push temperatures tomorrow afternoon into the mid to upper 70s
across the entirety of our forecast area, save for maybe
northern portions of Porter County if surface winds over Lake
Michigan can maintain a westerly or north-of-west direction
into the afternoon.

Ogorek


Wednesday through Monday:

On Wednesday, a semi-zonal upper-levevel ridge centered over
the northern United States will extend eastward toward the Great
Lakes as a surface high pressure system settles over the
southeast. With experimental smoke model guidance indicating
clearing mid-level concentrations giving cautious confidence to
mostly sunny skies, increasing 850mb temperatures toward +18 to
+19C should translate to highs in the mid to upper 80s areawide
including up to the Lake Michigan shoreline. Return moisture
flow around the perimeter of the surface high will lead to
rising humidity levels as well, altogether making for a
quintessential mid June day.

Wednesday evening, pressure falls in the Plains south of a
strengthening high pressure system in central Canada will
support development of a low-level baroclinic zone from the
northern Plains to the Great Lakes. Ensemble model guidance
advertises a series of subtle upper-level ripples propagating
atop the baroclinic zone Wednesday night through Friday, which
will serve as the focus for episodic clusters of showers and
thunderstorms (some of which could be strong to severe). At this
point, ensemble model guidance favors the preferred axis of
thunderstorm activity remaining just to our north in Wisconsin.
However, convectively-invigorated baroclinic zones have a habit
of ending up further south than models would suggest.
Accordingly, will advertise nearly continuous chances (30 to
60%) for showers and storms from Wednesday night through at
least Friday, keeping in mind many hours will be dry.
Temperatures will be modulated by the eventual cadence and
timing of individual thunderstorm clusters, though conceptually
a general theme of cooler temperatures near the Wisconsin border
and Lake Michigan shoreline with warmer temperatures near US-24
should prevail.

Chances for showers and storms will continue into the weekend
as a pesky upper-level low meandering through the southern
Plains eventually lifts east-northeastward toward the Great
Lakes. Exactly how, and when, the low arrives will be subject to
refinement in later forecast packages as the overall regime is
one that naturally carries lower than average forecast
confidence. However, conceptually, would expect a couple days of
cooler temperatures owing to more cloud cover and increased
coverage of rain.

Looking toward next week and beyond, there is an emerging
signal within ensemble model guidance for hot and humid
conditions to materialize in the general Midwest region (looking
at the June 16-20 timeframe or so). With increasingly hot and
humid conditions may come with increased threat for severe
weather as well. (The EPS mean MUCAPE is already nearing 1500
J/kg in the June 18/19 timeframe, a remarkably strong signal for
an environment supportive of severe storms for a 51-member
ensemble 10 days out).

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 639 PM CDT Mon Jun 9 2025

Key aviation messages for the 00Z TAFs:

- Gusty west winds diminish quickly with sunset this evening.
  Winds become breezy west again Tuesday, though not as strong
  as today.

- Area of wildfire smoke upstream across the Dakotas/MN may
  spread across the local area Tuesday. Low confidence in
  coverage or any surface vis impacts.

Early evening surface analysis depicts low pressure passing
north of the Great Lakes region, with a trailing cold front now
well east of the terminals across lower MI, IN and downstate IL.
In the wake of the front, dry conditions were occurring with
breezy westerly surface winds and VFR stratocu bases in the 6-8
kft range. Both winds and cloud cover will diminish with sunset.
The surface low will continue to pull away from the region on
Tuesday, with redevelopment of a diurnal VFR stratocu layer by
mid-late morning. This layer may briefly be broken in coverage
before trending scattered midday into the afternoon hours.
Surface winds will remain westerly, becoming breezy with gusts
near 20 kts by late morning, though winds too should ease
gradually later in the afternoon.

Wildfire smoke is evident in visible satellite imagery this
evening across the eastern Dakotas and western MN, with a few
spots reporting MVFR/low-VFR vis in haze. Smoke is forecast to
spread east-southeast across the local area again Tuesday and
may make for hazy conditions aloft, though confidence is low in
any surface vis impacts. Will likely need to handle this
tactically into tomorrow as we see how conditions trend

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 8 PM CDT this evening for the IL
     and IN nearshore waters.

&&

$$

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