textproduct: Chicago

KEY MESSAGES

- Showers likely late Friday into Friday night, especially across our south/southeast portions of the forecast area.

- Spotty shower chances at times during the extended holiday weekend, though many dry hours expected.

- Return to somewhat above average temperatures expected next week, though cooler temperatures expected near the lake.

DISCUSSION

Issued at 246 AM CDT Thu May 21 2026

Early morning surface analysis places 1030 mb high pressure over the northern Great Lakes. This will maintain breezy northeast to easterly surface winds, reinforcing a cool/dry low level air mass across the forecast area as the high slowly drifts east through Friday. Aloft, the upper pattern generally features troughing across the western CONUS, with west- southwesterly upper level flow from the Plains to the Great Lakes. Within this flow, a a subtle mid-level short wave was evident in GOES vapor imagery tracking east-northeast from NE/KS. A few high-based convective showers (isolated thunderstorms earlier) were noted from northeast KS into far southwest IA in association with this wave, along the northern periphery of a 7-7.5 C/km mid-level lapse rate/weak MUCAPE plume. Several CAMs indicate some spotty precip potential into WI/far northern IL as the wave tracks into our region later this morning, though with such dry low-levels and high convective bases (~10 kft) chances of actual measurable rain appears quite low. Have added a slight chance (<15%) pop roughly north of a Sterling to Waukegan line for sprinkles from after daybreak through late morning for this potential. Otherwise, dry conditions are expected today through Friday morning. Breezy northeast winds with gusts 20-25 mph will keep temperatures on the cool side again today, with highs from the 50s along Lake Michigan to the low-mid 60s farther inland and some upper 60s south of the I-80 corridor. Those breezy winds will also continue to produce hazardous swimming conditions at Lake Michigan beaches through this morning, before easing a bit this afternoon.

Much farther to our west, a jet-streak digging southeast across the northern Rockies is progged to carve out a stronger short wave across the Plains Friday morning, before lifting northeast across the upper Midwest late Friday/Friday night. Meanwhile, a weaker southern stream wave is forecast to lift northeast from TX into the lower OH Valley with a corresponding surface low which tracks north of the Ohio River. Guidance has struggled a bit with the degree (if any) of phasing between these two disturbances, as well as the resulting rainfall footprint across our area especially Friday night. Global ensembles generally favor our south/southeast half of the forecast area for highest rain chances, with the CMCE and EPS (to a lesser extent) still producing 60-100% pops, with the NBM blend on the higher end of the spectrum. There is a play however where particularly our northwest half of the cwa ends up with little/no precipitation during this time, and have limited NBM pops some there. Thunder potential still appears fairly low, with only the Canadian GEM guidance spreading MUCAPE into our southeastern cwa Friday night.

Scattered showers may linger into early Saturday morning as the main short wave trough axis shifts northeast across the area. While we remain beneath the southern periphery of the larger scale upper trough, forcing for precipitation during the day appears nebulous and weak subsidence behind the departing morning wave may support many dry daytime hours. Shower chances do look to increase from the west late in the day/evening however, as guidance depicts another mid-level short wave rounding the base of the upper trough. The pattern remains unsettled Sunday into Monday, as a series of weak waves ripple through somewhat less amplified westerly flow aloft. Ensemble QPF progs generally indicate Sunday afternoon may be favored for a somewhat higher shower/thunderstorm threat, though overall weak surface features and lack of significant deep moisture lends to low confidence in any significant precip coverage through the end of the holiday weekend. There remains decent agreement in a continued gradual warmup (albeit still with some lake cooling) from Saturday into mid-next week with daytime highs in the 70s.

Ratzer

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 623 AM CDT Thu May 21 2026

Forecast concerns for the terminals...

- Breezy east-northeast winds this afternoon with gusts around 25 kts.

- Non-zero chance (10-15%) for sprinkles light showers at RFD this morning and at all terminals Friday morning.

A broad surface high continues to reside over the northern Great Lakes which will promote generally quiet weather conditions for this TAF period. However, there is a weak disturbance lifting across IA this morning which has lead to some sprinkles and light showers at times. While these showers should wane as they encounter the drier air over northwest IL, some of the deeper cores noted on radar have given sufficient confidence to justify adding a PROB30 to RFD for light showers for a couple of hours this morning. Otherwise, VFR conditions are expected through the TAF period. There is another low chance (10-15%) for some isolated showers/sprinkles Friday morning areawide, but given the modest forcing confidence is too low for any formal TAF mention at this time.

Wind wise, directions remain east-northeastly through the period. Speeds will increase through this afternoon with gusts peaking around 25 kts, especially at the Chicago area terminals, this afternoon. Gusts will subside this evening and remain around 7-10 kts overnight into Friday morning.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement through Saturday afternoon for ILZ006- ILZ103-ILZ104.

IN...Beach Hazards Statement through late tonight for INZ001.

Beach Hazards Statement through this evening for INZ002.

LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL nearshore waters.

Small Craft Advisory until 7 AM CDT this morning for the IN nearshore waters.