textproduct: Chicago

KEY MESSAGES

- The next few days will be characterized by relatively cool temperatures, afternoon showers, and chilly nights.

- Patchy frost may develop the next few nights with a widespread frost Friday night into Saturday morning

- Slightly warmer, but also wetter, conditions may arrive by this weekend.

DISCUSSION

Issued at 123 AM CDT Wed Apr 29 2026 Upper-level troughing with embedded shortwaves now encompasses much of the northern United States. With little in the way of change in the upper-level pattern through the next 48 hours, today and Thursday will be more or less the same with seasonably cool temperatures and diurnally-driven isolated to scattered showers. Highs today and tomorrow will reach the upper 50s to lower 60s, except the upper 40s to lower 50s lakeside due to lake breezes. Each afternoon will not be a washout, though isolated to scattered showers (perhaps with embedded graupel) will move through the area during peak heating. Finally, overnight lows will fall into the mid to upper 30s. Patchy frost can't be ruled out the next few nights where surface decoupling is most efficient.

On Friday, a more pronounced upper-level shortwave will drag a pool of even cooler air into the region. With 850mb temperatures of -5 to -6C, highs will stay decidedly in the 50s (upper 40s lakeside). A diurnal flare to showers is expected once again, perhaps with better coverage compared to today and Thursday given cooler low-level temperatures (more diurnal instability).

Friday night continues to look like the chilliest night of the pattern as a surface high pressure system shifts into the Great Lakes allowing for surface winds to drop off and skies to clear. The speed at which skies clear will be important to the eventual overnight lows. With that said, current indications are most areas should fall into the low to mid 30s. As a result, we will continue to highlight Friday night/Saturday morning as the period to watch for widespread frost.

This weekend, the aggregate upper-level troughing is expected to shift eastward placing the Great Lakes in broad northwesterly flow. At least some moderation in temperatures is expected by early next week, though a parade of shortwaves will lead to incrementally increasing chances for showers and perhaps a few thunderstorms. Ensemble guidance favors the general pattern of upper-level cyclonic flow in the northern United States persisting into the second week of May, suggesting that temperatures should remain seasonable (if not a hair below average) until further notice.

Borchardt

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 1236 AM CDT Wed Apr 29 2026

Forecast concerns include...

Chance of showers overnight and again this afternoon. Wind directions through mid afternoon.

Scattered showers will be possible early this morning with the bulk of this activity remaining just south of the terminals. There will be another chance of showers this afternoon that may eventually need prob/tempo mention with later forecasts.

Winds are expected to favor a north/northwest direction early this morning and then more northerly around/after daybreak, eventually shifting northeasterly with a lake breeze boundary this afternoon. Previous wind trends look reasonable and made no changes. However, only medium confidence regarding which side of north winds will favor at ORD/MDW through early afternoon. cms

LOT WATCHES/WARNINGS/ADVISORIES

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