textproduct: Chicago

KEY MESSAGES

- Chance of thunderstorms today, some possibly becoming severe in the afternoon.

- Turning hotter and more humid into early next week.

DISCUSSION

Issued at 310 AM CDT Wed Jun 24 2026

A mid/upper-level trough, and an attendant surface low, moving into the Upper Midwest this morning, will move across the western Great Lakes later today into tonight. As it does, our primary forecast concerns will center around thunderstorm coverage, timing and severity today. Initially, we will be monitoring an area of ongoing showers and non-severe thunderstorms to our north- northwest across far southern MN/northern IA eastward into southern WI. This activity is expected to gradually sag southward across far southern WI towards the IL state line by around daybreak this morning. We are not expecting any severe threat with this morning activity, but there is likely to be some scattered showers and a few thunderstorms this morning, particularly across far northern IL (I-88 and north). Thereafter, attention turns towards the likelihood for additional thunderstorm development this afternoon into this evening.

This afternoon, a moistening low-level airmass (dewpoints climbing into the low to mid 60s) is expected to diurnally destabilize in the wake of this mornings activity, and in advance of an approaching cold front. As this occurs, there continues to be a general consensus that this will support scattered thunderstorm development across southern WI southward into northern IL after 2 to 3 PM. The environment in which these storms develop will be amply sheared, owing to the presence of an enhanced belt of westerly mid-level flow (45-50 kt) moving out across the warm sector. Accordingly, storm organization and an associated severe threat will exist with the strongest clusters later today into early this evening. It appears the primary severe threats will be damaging wind gusts in excess of 60 mph. However, a few instances of severe hail will also be possible, particularly in association with any supercells. Storm motions will ultimately favor scattered storm clusters and supercells to shift east-southeastward across northeastern IL into northwestern IN into this evening before weakening later in the evening with the passage of the cold front.

On Thursday, the surface cold front is expected to stall out and become west-to-east oriented across downstate IL and IN as the next surface low sets up across the southern Plains. This front will continue to be the main focus for additional shower and thunderstorm activity on Thursday, and given its placement to our south, most of the day on Thursday is looking to be dry, with only a low (20%) chance of a few showers. Thereafter, the next impulse and wave of surface low pressure is forecast to track eastward across the Mid-Mississippi Valley into Friday. As this occurs, the focus for an area of rain activity may begin to to shift back northward into southern sections of our area (mainly areas south of I-80) Thursday night and on Friday. Confidence on how far north this area of precipitation is able to get into our area remains low at this time, owing to our region likely remaining along the northern periphery of this system.

This weekend into next week, ensemble forecast guidance continues to be in good agreement with a larger scale weather pattern change taking place across the central part of the country. The main feature of this transitioning pattern is expected to be the development of a subtropical ridge right across the Mississippi Valley into the Great Lakes into early next week. Locally, this is expected to result in a turn towards hotter and more humid weather and an end to the below average conditions. However, the extent of the hot and humid weather in our region will ultimately be dependent upon convection trends along the northern periphery of the upper ridge.

KJB

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1249 PM CDT Wed Jun 24 2026

Forecast concerns include...

Scattered thunderstorms this afternoon into this evening. Wind directions through this evening. Northeast wind shift/lake breeze Thursday evening.

An area of showers will move across the Chicago terminals over the next few hours with brief mvfr vis/cigs and possibly begin to dissipate. Scattered thunderstorms are developing across southwest WI and this activity is expected to increase in coverage as it moves southeast across the terminals during the mid to late afternoon. There may be a second round of showers and scattered thunderstorms during the mid/late evening and while confidence is low, opted to include prob thunder mention for this potential, which may be dependent on how the first round of storms evolves. Isolated showers may linger into the overnight hours.

There are various boundaries from the current showers and earlier showers this morning that make prevailing wind directions challenging. A general west/northwest direction is expected for the next few hours and then a turn back to the southwest is expected later this afternoon. Winds may turn to the southeast or easterly behind the first round of storms, then possibly become light and variable during the mid evening. Prevailing light westerly winds are expected overnight, turning more west/northwest Thursday with speeds to 10kt. A lake breeze is expected to develop Thursday afternoon and move inland with winds turning northeast at the Chicago terminals early Thursday evening. There is also a low chance for a few showers to develop along the lake breeze Thursday afternoon. cms

LOT WATCHES/WARNINGS/ADVISORIES

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