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 /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 116 AM CDT Wed Jun 24 2026

Key Messages:

- Periods of showers are expected today, with probable scattered thunderstorms in the area this afternoon and evening.

An approaching mid/upper-level disturbance and associated low pressure system will result in periodic shower and storm chances today. Existing shower and thunderstorm activity across southern Wisconsin, southern Minnesota, and northern Iowa early this morning should gradually decay with time and eastward extent, but the remnants of this activity may nevertheless persist into our area this morning and bring about an initial period of showers. RFD stands the greatest chance of seeing some rain this morning, and there is also a lower-end chance (~15%) of a few lightning strikes occurring near there this morning as well.

Additional waves of showers and storms are likely to develop and track southeastward through northern Illinois and northwest Indiana this afternoon and evening. Pinpointing precisely where and when the storms may occur remains a challenge -- partly because the morning showers and associated cloud cover will affect how quickly the necessary destabilization to support this convection will be able to occur, and partly because of uncertainties pertaining to where any initiating surface boundaries may be present when sufficient destabilization is eventually realized. As a result, have a relatively low confidence 6-hour-long PROB30 group for TSRA present in all five of our TAFs during the mid-afternoon and early evening, when the potential for thunderstorms appears to be greatest at the terminals. Refinements to this TSRA mention (and other elements of the TAFs related to the shower and thunderstorm activity) will likely be needed as observational trends become apparent later today. Wherever storms do occur today, gusty wind shifts and sub-VFR visibilities and ceilings may also occur.

Otherwise, VFR conditions with predominantly southwesterly winds are expected through a majority of the TAF period.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

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