textproduct: Chicago

KEY MESSAGES

- Cooler daytime temperatures, afternoon showers, and chillier nights through the end of the week

- Patchy frost possible tonight and Friday morning, with the potential for widespread frost Saturday morning.

- Warmer and wetter conditions potentially late in the weekend.

DISCUSSION

Issued at 149 PM CDT Wed Apr 29 2026

A 500 mb long wave trough over the upper Midwest will become a closed low overnight over southern Ontario and gradually move east through Saturday. Embedded shortwaves within the upper level troughing will provide occasional opportunities for showers this afternoon through Friday. Cloud cover this afternoon has limited daytime heating, but with an area of convergence near the lake due to the onshore winds, spotty showers are possible through the early evening, but will diminish quickly after sunset. Temperatures will fall into the 30s overnight. If winds decouple enough along with the decreased cloud cover tonight, patchy frost is possible tomorrow morning.

The wave is expected descend southward within the upper level pattern on Thursday afternoon. While the entire forecast area has a slight chance of a shower tomorrow, hi-res models are suggesting a slightly more southerly track to the wave leaning higher chances south of I- 80 tomorrow. Persistent northerly winds will continue to filter in cooler air to the region. As skies clear out again and winds diminish, there is another chance for patchy front Friday morning.

Guidance suggests yet another wave to descend down through the pattern on Friday providing another chance for showers Friday afternoon. The coldest air is expected to arrive overnight for probably the best chance for widespread frost to develop Saturday morning.

Weak ridging moving in from the west should finally break the string of shower chances and allow for a drier weekend. As winds turn to the southwest, it should filter in a (relatively) warmer air mass. It will not be a heat wave, but should help bring temperatures back up a little and approach the low 60s by Sunday. However, the next trough is expected to descend out of Canada Sunday providing the next chance for rain. There is still model disagreement on timing and location. With better forcing and instability, there could be some thunder embedded with these showers, but most guidance has the better instability to the south. Warmer temperatures will stick around early next week with another storm system potentially midweek.

DK

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1223 PM CDT Wed Apr 29 2026

Key Messages:

- MVFR to Low VFR CIGs this afternoon.

- A few passing showers at the Chicago terminals this afternoon.

- North-northeast winds at the main Chicago terminals this afternoon, with prevailing northwesterly winds expected at DPA and RFD.

A lake breeze boundary will act as the focus for showers this afternoon as a weather disturbance moves across the area. With the chances looking to be the best near the boundary, we have opted to add a tempo mention for showers at the main Chicago terminals through early evening. Some MVFR CIGs will also accompany the showers this afternoon.

While winds will primarily be north-northeasterly through the remainder of the day at ORD, MDW and GYY, expect predominately northwest winds at the inland terminals, at least through late this afternoon. Tonight, winds will become light northerly before settling northwesterly again on Thursday. There is also a small chance (20-30%) that another lake breeze leads to an easterly wind shift late Thursday afternoon. However, at this time we have opted to forgo a formal mention in the ORD and MDW 30 hour tafs. Otherwise, expect the possibility for additional scattered showers Thursday afternoon.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

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