Evanston, IL 60204 Weather

Key Messages

- Areas of fog, including potentially dense fog, may develop again late tonight into early Wednesday morning in and near the Chicago metro.

- An extended period of dry and above to much above average temperatures is expected through the upcoming weekend.

Discussion

Issued at 226 PM CDT Tue Oct 20 2026

An Omega block that is in place over the CONUS is expected to persist through the end of the week. The associated ridge axis will only ever so slowly crawl eastward over the coming days, which will maintain broad surface high pressure across the region. As a result, dry conditions with an abundance of sunshine will continue through the remainder of the week with high temperatures remaining above to well above normal for this time of year. Daily lake breezes will cause the coolest (low- mid 60s) high temperatures to be observed near Lake Michigan each day.

Much like last night/early this morning, optimal radiational cooling conditions will likely allow for fog to develop late tonight into tomorrow morning and possibly again in the coming nights/mornings. This will particularly be the case in and near the Chicago metro within the footprint of the marine-influenced air brought inland during the daytime, where the fog could become dense once again.

There is pretty good ensemble agreement at this point in time that the blocking pattern will break down by early next week. This will allow for a cold front to drop through the region sometime on Monday or Tuesday, resulting in a return to cooler and more seasonable temperatures for the middle of next week. The frontal passage may bring a chance for precipitation to the area early-mid next week, but support for this across the latest suite of ensemble guidance is not ubiquitous, and there are considerable temporal differences with when this next potential opportunity for precipitation may arrive as well.

Ogorek

Aviation

Issued at 1255 PM CDT Tue Oct 20 2026

Key aviation forecast messages:

- IFR or lower VSBYs in BR/FG may develop again early WED AM.

The primary concern through the period is the potential for fog near Lake Michigan early Wednesday morning, some of which may become locally dense. Model guidance that performed well with this morning's dense fog depicts another round of fog development over a similar area and extends slightly farther southeast. Have accordingly included MDW with the reduced VSBYs as low as 1 SM with this update to hint at increasing confidence in fog development. If this signal persists and additional guidance begins to pick up on the potential for dense fog, LIFR (or lower) conditions may need to be introduced with later updates.

Otherwise winds will remain light (under 10 kt) initially out of the SE, turning E to ENE behind a weak lake breeze this afternoon. Winds then ease and become light and variable again overnight eventually settling into a SSW direction after daybreak Wednesday.

Petr

Lot Watches

IL...None. IN...None. LM...None.