textproduct: Chicago

KEY MESSAGES

- Some light showers or sprinkles possible tonight, most areas not likely to receive more than a couple of hundredths of an inch of precip.

- Generally dry conditions expected through much of the upcoming work week with the next appreciable rain chances not until Friday into next weekend.

DISCUSSION

Issued at 119 PM CDT Sun May 31 2026

Strong high latitude blocking upper ridge over central Canada is resulting in a rather wonky pattern with a WNW-ESE oriented mid-upper level trough extending from the northern Rockies/Pacific NW to the Cornbelt. Embedded lower amplitude shortwaves, some convectively enhanced, are rounding the base of this trough and running into the southern flanks of the upper ridge. One such disturbance has been resulting in a band of showers from northeast IA into central IL this afternoon. These showers have been struggling to make any meaningful eastward progress as they encounter a very dry easterly low level flow. Can't rule out a few light showers making into our far western CWA very late this afternoon into this evening, though virga seems to be the more likely outcome.

Tonight, weak low-mid level warm air advection to our west associated with the aforementioned "sideways" upper trough and some strengthening low-mid level cold air advection over the western Great Lakes will result in a tightening of low-mid level baroclinic zone from southern WI into northern IL. This increased baroclinicity is most noted in the 850-700mb layer where a strengthening frontogenetic circulation will likely result in some moderately strong ascent. Air mass below this f-gen circulation will remain very dry, so it will be a bit of a battle to see whether or not the ascent with the frontogenesis will be enough to penetrate the low level dry air mass. Inherited chance of sprinkles tonight for most of the area and this seems reasonable given the dry air and potential that precip may not even reach the ground. One note of caution, guidance does depict rather deep area of negative saturated EPV near the vertical f-gen circulation. These type of set-ups can sometimes overperform when, which could result in a narrow band of showers heavy enough to wet the ground overnight.

Any showers/sprinkles late tonight should end by around or just after sunrise with dry conditions expected much of the rest of the week. Lake breeze, enhanced by synoptic northeast winds, should result in a sizable footprint of lake cooled air Monday through Wednesday. The most significant cooling relegated to areas very near the lake.

The strong blocking ridge over Canada is progged to breakdown later this week as a strong trough moves across far southern Canada toward Hudson Bay by Friday. This should push the high that's provided the area with over a week of onshore flow to move east and allow for southwesterly low level flow to develop Thursday into Friday. This should advect a warmer and more humid air mass into the area, likely including areas right up to the lakefront both days. A cold front is likely to sag southward across the western Great Lakes region Friday into Saturday with increasing chances for at least periodic showers/storms. Some variances emerge in the medium range guidance heading into the weekend, but a more unsettled pattern could support at least chances of showers and storms in the area through next weekend.

- Izzi

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1212 PM CDT Sun May 31 2026

VFR with no significant concerns. Occasional sprinkles/light rain may make it as far east as the Chicago metro terminals late tonight into early Monday. With RFD having the best chance of periodic -RA this evening and overnight, added in PROB30 mention there. East-southeast winds inland and northeast winds near the lake today will trend to a northeasterly directional area wide on Monday.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

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