NWS Chicago Decision Support Briefing - Forecast

891
FXUS63 KLOT 240611
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
111 AM CDT Fri Apr 24 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms through this afternoon
ahead of a cold front.

- Seasonable and dry conditions over the weekend.

- Scattered severe thunderstorms Monday along with heavy rain
and possible localized flooding.

&&

.DISCUSSION...
Issued at 111 AM CDT Fri Apr 24 2026

While storms continue to slowly dissipate across far west and
northwest IL early this morning, a strong outflow boundary will
need to be monitored as it continues into the western cwa early
this morning. The expectation is for the winds with this
boundary to slowly weaken. Scattered showers and isolated
thunderstorms will be possible through daybreak with a gradual
weakening trend expected. There may be a lull in precipitation
during the mid morning hours and then additional showers and at
least a few thunderstorms are expected to develop along/ahead of
the main cold front. Quite a bit of uncertainty for coverage
with this activity but likely pops seem reasonable from this
distance. This activity will quickly shift east of the area by
mid/late afternoon. The best chance for any stronger storms or
possibly isolated severe thunderstorms appear to be east of the
local area this afternoon.

Winds will shift northerly tonight and remain northeasterly
Saturday and easterly on Sunday as cooler air spreads back
across the area. Low temps both Saturday and Sunday morning are
expected to be in the 40s. Highs inland will be well in the 60s
and likely lower 70s Saturday, low/mid 70s Sunday, but much
cooler temps are expected closer to Lake Michigan.

The models are in general agreement for low pressure to develop
over the southwest Plains Sunday which will then move northeast
across the western Great Lakes Monday night as a cold front
moves across the local area Monday night. Current trends suggest
at least a broken line of strong/severe thunderstorms developing
west of the local area and then quickly moving east of the area
by mid/late Monday evening. With precipitable water values
approaching 1.5 inches by late Monday afternoon, heavy rain may
lead to localized flooding. cms

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1200 AM CDT Fri Apr 24 2026

LLWS conditions will continue through the overnight hours with
flow at 2km of 45-50k (per the KLOT VWP).

A line of showers and thunderstorms marching toward the
Mississippi River is expected to continue decaying as it moves
into northern Illinois. Nevertheless, a robust cold pool should
allow for at least modest forced ascent to support showers and a
few thunderstorms as far east as I-39 and perhaps to the Lake
Michigan shoreline. Will maintain the inherited PROB30 groups
for thunder and gusty westerly convective winds generally
between 08-10Z at the Chicago terminals, but promote to a TEMPO
group at RFD from 07-09Z. Showers may continue behind the
leading edge of the cold pool or as stratiform rain streams
northeastward behind additional line segments moving toward
central Illinois.

Toward and after daybreak, current thinking is that showers
will taper giving way to SCT to BKN MVFR cigs. Winds should
favor a southwesterly directly with speeds near 10kt. With time,
forecast soundings depict minimal capping ahead of an
approaching cold front by early afternoon. So, the inherited
PROB30 groups for another round of showers (perhaps a few
thunderstorms) favoring the afternoon hours looks good.

The cold front will move across the airspace during the late
afternoon hours leading to a northwesterly wind shift. Currently
am not expecting any MVFR cigs behind the frontal passage.
Toward the end of the TAF package, winds will veer
northerly near Lake Michigan, leading to onshore flow.
Conceptually, the pattern will be supportive of at least FEW to
SCT IFR cigs coming off the lake, if not even some patchy fog.
Will introduce SCT006 at ORD/MDW/GYY for now in favor of
refinement in later TAF packages.

Borchardt

&&

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

&&

$$

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