textproduct: Chicago

KEY MESSAGES

- Generally dry conditions through mid-week with seasonable temperatures inland and cooler conditions near the lake.

- Rain chances return Friday and may linger through the weekend.

DISCUSSION

Issued at 201 PM CDT Mon Jun 1 2026

A shortwave trough continues to dive southward across the northern Great Lakes with a band of mid-level moisture being noted ahead of the trough from northern MN to the Ohio River Valley. While a few radar echoes have developed ahead of the shortwave within the moisture axis, the high cloud bases (7000-8000 ft) and dry sub-cloud layer (temp-dew point spreads 20-30 degrees) are preventing anything from reaching the surface. Therefore, dry conditions are expected to prevail as the shortwave pivots through this evening with skies expected to gradually clear behind the wave. Despite the mostly to completely cloudy skies, temperatures have warmed into the 70s in many places with even a few sites tagging the lower 80s. The exception though is closer to Lake Michigan where onshore winds have capped temperatures in the mid to upper 60s. Temperatures will likely remain nearly steady through sunset before cooling into the lower 50s overnight.

High pressure will build back into the Great Lakes late tonight into Tuesday morning and will persist through the middle of the week. This will result in mostly sunny skies and generally light east-northeast winds through Wednesday before winds turn more southeasterly on Thursday. Temperatures during this period will remain in the seasonable to seasonably warm category with highs in the upper 70s to mid-80s each day. However, with persistent onshore winds Tuesday and Wednesday, temperatures near the lake will be notably cooler in the 60s to around 70.

While we enjoy the pleasant spring weather, the broad upper low that is spinning over the Mountain West will begin to drift eastward as a deepening Pacific trough moves onshore. As the upper low moves east it is forecast to broaden into a shortwave trough which will in turn begin to push the baroclinic zone stalled across the Plains eastward as well. The forcing from the baroclinic zone and trough should result in an uptick in shower and thunderstorm coverage across the Midwest by Thursday that will eventually spread into the Great Lakes during the Friday and Saturday timeframe. While guidance is in generally decent agreement on this systems evolution through weeks end, there is still some uncertainty in exact timing rain will return locally due to intensity differences with the aforementioned eastward propagating trough. Regardless, it does look as if a period of wet weather will impact the area to close out the week and begin the weekend.

In the wake of this system is where forecast confidence becomes much lower as guidance varies greatly on how the pattern will evolve behind the initial trough. The GFS/GEFS solutions continue to favor the initial trough arriving stronger and as result having a more formidable frontal zone to push through northern IL and northwest IN. Therefore, in the wake of the front the GFS/GEFS indicates stronger ridging redeveloping and resulting in another period of tranquil weather with persistent east-northeast winds from Sunday into next week. However, the Euro and Canadian deterministic and ensemble solutions are notably weaker with the initial trough and therefore have a much slower and more diffuse frontal zone moving through. Due to the weaker forcing, the Euro/Canadian solutions show weaker ridging redeveloping on Sunday and thus allowing a secondary shortwave to eject out of the southern Plains towards the mid-Mississippi Valley and western Great Lakes. If this solution pans out then we would be looking at a shift towards a warmer and more stormy pattern with several periods of showers and thunderstorms possible this weekend into next week.

At this stage, the high degree of uncertainty makes confidence too low to favor any particular solution. So our official forecast will maintain some chances for showers and storms through the weekend and into next week as the NBM's probabilistic guidance favors the Euro/Canadian solutions, but will need to watch this period closely for emerging trends. That said, anyone with outdoor plans this weekend or next week should keep checking back for updates as the extended forecast is likely going to shift a lot over the coming days as guidance tries to resolve this pattern.

Yack

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1202 PM CDT Mon Jun 1 2026

VFR with no significant concerns. Northeast winds will prevail through the period, peaking at around 10 kt this afternoon, and then up to 15 kt Tuesday afternoon with sporadic ~20 kt gusts. Current 6-7kft AGL CIGs will scatter by this evening.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

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