Des Plaines, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

631
FXUS63 KLOT 291201
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
701 AM CDT Thu May 29 2025

.KEY MESSAGES...

- Gusty thunderstorms may move across the region Friday
  afternoon and evening. The Storm Prediction Center has a Level
  1/5 threat for severe weather east of I-39.

- There is an increasing signal that smoke from wildfires in
  Manitoba will stream into the Midwest and Great Lakes as early
  as Friday, and potentially linger through the weekend.

- A pattern change is anticipated during the first week of June
  and will result in the arrival of more summer-like
  temperatures, followed by increasing chances for storms mid to
  late week.

&&

.DISCUSSION...
Issued at 337 AM CDT Thu May 29 2025

Through Friday night:

The dirty Rex block that has remained entrenched across North
America is finally in the process of breaking down. Water vapor
imagery early this morning shows upper-level low component over
the Great Lakes is in the process of becoming elongated, which
now stretches from the northern Plains to the northeastern
United States. Our local area is barely on the outer/southern
edge of the upper-level vorticity ribbon surrounding the
elongated circulation, with associated neutral height
tendencies. Minimal low- to mid-level vertical motion in tandem
with broken cloud cover, light winds, and recent rainfall has
accordingly allowed for patches of fog, some dense, to develop
early this morning especially in outlying/rural areas. The good
thing about fog this time of year is that it doesn`t last long
after sunrise, as the high sun-angle efficiently facilitates
thermal mixing even through broken cloud cover. So, fog should
abate soon after sunrise.

Today, the elongated upper-level low will decompose into a
positively-tilted trough while drifting southeastward across the
Midwest. As this occurs, modest upper-level height falls and
the approach of a weak frontal boundary from the north may allow
for a few showers to develop this afternoon near the Wisconsin
border. With that said, chances for showers appear to be lower
than it looked in prior days (now only a 10 to 15% chance).
Partly cloudy skies and minimal thermal advection (only about
15kt of flow from the surface to 15kft) support highs a few degrees
warmer than yesterday and in the lower 70s. The exception, of
course, will be near Lake Michigan where highs will remain in the
upper 50s to lower 60s.

Tonight, the aforementioned positively-tilted upper-level
trough will swing into the Ohio River Valley. As the northern
edge of the trough moves overhead, a shower or two may sprout
anywhere across our area. With that said, chances for measurable
rain at any given location appears to be 10% or lower. Tonight
otherwise looks quiet with a continuation of light winds. Lows
will be similar to early this morning and in the lower 50s.

By Friday, the upper-level trough that once was our upper-
level low will be well southeast of our area. A mostly sunny
start to the day should allow for temperatures to warm nicely
into the early afternoon, with highs expected to reach the mid
to perhaps upper 70s. Increasingly deep boundary layer depths
will afford efficient mixing into a tightening surface pressure
gradient, supporting northwesterly wind gusts of 25 to 35 mph
particularly during the afternoon. Accordingly, the marine
airmass should be kept offshore (for once), allowing for warm
temperatures to finally reach the lakeshore.

Friday afternoon, a sharp upper-level trough anchored by a 60kt
500mb speed max is expected to dive southeastward out of
central Canada and into the Great Lakes. While low-level
moisture will be meager ahead of the wave, steepening low- to
mid-level lapse rates will support the development of 500 to
1000 J/kg of MUCAPE by late afternoon. The overlap of
instability within a modestly sheared kinematic profile
(characterized by "southward" pointing straight hodographs)
suggests that a few semi-organized clusters of gusty
thunderstorms may develop Friday afternoon across Wisconsin,
which would be poised to dive into northern Illinois and
northwestern Indiana Friday evening. After collaboration with
NWS Green Bay, NWS Milwaukee, and the Storm Prediction Center, a
Level 1/5 threat for damaging winds and hail was introduced in the
Day 2 outlook, valid for Friday, mainly east of I-39.

One last thing... Over the past few days, several large
wildfires have developed in central Canada and especially
Manitoba. With the upper-level low leaving our area today and
tonight opening the door for northwesterly low- to mid-level
flow across the Upper Mississippi River Valley, wildfire smoke
may begin to stream southeastward toward the Great Lakes. The
HRRR and Canadian Smoke models show such a scenario, with mid-
level smoke reaching northern Illinois and northwestern Indiana
as early as Friday afternoon (which would lead to the hazy/milky
look to the sky). Perhaps more concerning is a signal for near-
surface smoke to reach our area as well, particularly Friday
evening when mixing profiles will be deep. For now, will leave
any smoke (mid-level haze, near-surface visibility restrictions,
etc) out of the forecast, though this will be something to
monitor closely going forward.

Borchardt


Saturday through Wednesday:

Saturday`s weather will, in part, be dictated by how quickly a
backdoor cold front associated with the upper-level trough
diving from Canada into the Great Lakes cuts across our forecast
area Friday night into Saturday. Diurnal
heating/destabilization and low-level confluence could lead to
showers and perhaps a few storms developing along the front
Saturday afternoon wherever it is positioned. Thus, a slower
frontal passage should support shower chances in our forecast
area on Saturday, but a faster frontal passage would expel those
chances to our west and south. Similarly, temperatures will
also largely be governed by the southward and westward progress
of the front, with upper 50s to low 70s temperatures likely to
be observed behind the front (coolest near the Lake Michigan
shore), while locations that remain south/west of the front
through the afternoon may be able to make a run for the low 80s.

Sunday will likely remain dry across our forecast area as
surface high pressure begins to develop in the region ahead of
an approaching upper-level ridge. Daytime heating of the air
mass over the region should tend to favor slightly warmer
temperatures being observed relative to Saturday in most
locations, through continued, albeit weaker, onshore flow should
continue to support a lake shadow of cooler temperatures some
distance inland from Lake Michigan. One additional wildcard for
temperatures on both Saturday and Sunday will be the coverage
and opacity of any lingering Canadian wildfire smoke, as the
persisting northerly to northwesterly flow aloft should tend to
promote the continued transport of smoke particulates
originating from Manitoba and Alberta in our general direction.
If confidence increases in a relatively thick veil of smoke
hovering over the area on Saturday and/or Sunday, then up to a
few degrees may be need to be shaved off of our high temperature
forecast for the affected days.

Monday into Tuesday, the axis of the aforementioned amplified
upper-level ridge should slide eastward across the Midwest.
Both days look like they will be warm and dry (assuming that
the outlier 00Z GFS and GEFS solutions don`t verify), with
southerly flow and at least filtered sunshine allowing for high
temperatures to climb solidly into the 80s, and possibly even
into the low 90s in some locations. Eventually, a gaggle of
Pacific troughs will eject eastward into the central CONUS
during the mid to late week time frame, forcing the upper-level
ridge eastward. How all of these troughs will evolve and
interact with one another remains highly uncertain at this
vantage point, but the ensemble signal for a stormier period
occurring in the Midwest during the middle to latter part of
the upcoming workweek remains quite strong either way.

Ogorek

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 701 AM CDT Thu May 29 2025

Key Messages:

- Fog and low clouds will affect the terminals early this
  morning.

- Northeasterly/easterly wind shift expected this afternoon at
  GYY, ORD, and MDW behind a lake breeze.

- Low (15-20%) chance for isolated showers occurring near the
  terminals this afternoon.


Fog is being observed at the terminals this morning, resulting
in visibility reductions as low as LIFR (at GYY). Between this
fog and some lingering low clouds, MVFR or worse conditions are
expected to continue for up to a few more hours before things
gradually improve into the mid to late morning.

A lake breeze is expected to develop today and should push
inland this afternoon, causing a northeasterly/easterly wind
shift behind it. The precise timing of this lake breeze`s
arrival remains uncertain, and it`s possible that the lake
breeze may stall and/or not reach ORD or MDW until the very
late afternoon/early evening, at which point, it may become
washed out. Either way, flow on either side of the lake breeze
should largely tend to remain at or under 10 kts.

Lastly, there is a lower-end chance for isolated showers to
develop near the terminals this afternoon. The overall
likelihood of a shower occurring over any one TAF site is only
about 15-20% -- not high enough to warrant a PROB30 or TEMPO
group for -SHRA or a VCSH mention at this time, but couldn`t
rule out eventually needing such a mention as observational
trends become clearer. If showers were to develop, the
probability of lightning occurring would be very low (under
10%).

Ogorek

&&

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

&&

$$

Visit us at weather.gov/chicago