Marine Weather and Tide Forecast for Chicago, IL

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.