940
FXUS63 KLOT 192330
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 PM CDT Thu Mar 19 2026

.KEY MESSAGES...

- Spring-like temperatures through the early weekend, though
  Lake Michigan will moderate temperatures along the shoreline.

- Cooler temperatures are expected early next week after a cold
  front passes on Sunday

&&

.DISCUSSION...
Issued at 211 PM CDT Thu Mar 19 2026

GOES-19 water vapor imagery shows moisture over the inner
mountain west riding over top of an upper level ridge located
over the desert southwest. This ridge is expected to remain
mostly in place through Saturday, if not expand and slide
eastward slightly. Today, clear skies has cause temperatures to
over-achieve and climb into the lower 60s (inland areas) earlier
than expected. In contrast, onshore flow has capped max
temperatures for the city of Chicago and other areas closer to
Lake Michigan in the 40s. As the ridge expands, mid level warm
air advection is projected to increase 850 mb temperatures to 15
to 18C. Temperatures will continue to warm up tomorrow and
Saturday with highs in the 60s and 70s. Shoreline locations will
remain slightly cooler with the lake influencing the onshore
flow. Moisture riding over the ridge and down the northwest flow
may allow periods of clouds at times through the weekend, but
no precipitation is expected.

The upper level ridge will begin to flatten into Sunday with
quasi-zonal flow projected to develop over the central CONUS
ahead of the arrival of an upper level trough. This trough is
expected to have a surface cold front associated with it that
will pass over northern Illinois. Confidence lowers dramatically
in timing of the front and high temperatures for Sunday given
the disagreement between models and even with the run-to-run
consistency of individual models. If later runs verify, the
current high temperature could be underdone, whereas if that
front comes racing down the lake, much cooler temperatures
could arrive much sooner and drop temperatures substantially
(especially along the lakefront). Lastly, the NBM is still
showing a pool of moisture moving in with the front, so no
changes to the slight chance PoPs that the blend gives;
especially since amounts look fairly limited.

A cooler air mass is expected behind that front. Lows
potentially could drop below freezing, while afternoon
temperatures only climb into the 40s. Models are suggesting that
another ridge will move out of the southwest through the middle
of next week. That should help temperatures moderate and start
to warm again back into the 50s. With northwest flow over the
area, a stray impulse cannot be ruled out mid/late next week
that could bring a chance for rain, but without any real model
consensus, confidence is low.

DK

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 630 PM CDT Thu Mar 19 2026

Forecast concerns for the terminals...

- Lake enhanced cold front to result in northeast winds at the
  Chicago terminals and GYY Friday afternoon.

- Chance for MVFR ceilings to develop Friday evening, but
  confidence on their coverage and arrival is low.


A weak surface high continues to drift across the Mississippi
Valley which is resulting in a pleasant evening across the
terminals though a broad upper trough over the Great Lakes is
starting to filter in more cirrus cloud cover. A lake breeze
continues to gradually washout as it progresses across north-
central IL this evening resulting in period of 10-12 kt winds in
its wake. Winds this evening will continue to diminish into the
5-10 kt range and become more southwesterly after midnight with
SCT to BKN VFR cirrus expected through the night. However, with
temperature-dew point depressions forecast to inch into the 1-3
degree range there is a chance (10-15%) for patchy fog to
develop once again especially across northwest IL. Since winds
will be a bit elevated overnight confidence on any fog
materializing is too low for a TAF mention but will continue to
monitor trends.

Heading into Friday, a cold front will move through northern IL
Friday morning which will result in winds becoming northwesterly
and increasing into the 10-12 kt range. That said, the front
also looks to enhance a lake breeze Friday afternoon which
should push through the Chicago area terminals and GYY between
19z and 21z turning winds northeasterly in its wake. As is
common with lake breezes confidence on the exact arrival time is
low, but for now have maintained the 19z-20z mentions in the
TAFs respectively. Generally, VFR conditions are expected to
prevail through Friday evening but there is a growing signal in
guidance for some MVFR clouds to develop and ooze over the
terminals. Given that forecast soundings show moisture being
somewhat limited have opted to maintain the SCT020 mention in
the TAFs for now but would not be surprised if official ceiling
mentions are needed with future updates. That said, a period of
MVFR ceilings does look to develop after sunset and linger
through the end of the 30-hour TAF period.

Yack

&&

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

&&

$$

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