textproduct: Chicago

KEY MESSAGES

- Dangerous heat wave continues into Thursday, with daytimes highs in the low to mid 90s and peak afternoon heat indices of 100 to 105 degrees (locally higher). - While not a complete wash out, thunderstorm chances increase late Thursday, with a couple of waves of showers and thunderstorms expected Friday into the 4th of July weekend. Some storms may be severe and produce heavy rainfall.

DISCUSSION

Issued at 208 PM CDT Tue Jun 30 2026

The ongoing heat and humidity continues to be the primary weather story through Thursday.

A persistent upper-level ridge, with H5 heights in excess of 596 DAM, will remain centered across Kentucky and Tennessee through Wednesday, before gradually expanding eastward towards the central Atlantic coast for the second half of the week. Strong capping under this ridge will continue curtail the threat for showers and thunderstorms locally through at least Thursday afternoon/evening. Accordingly, unabated diurnal heating of the very moist low-level airmass will push afternoon high temperatures in the low to mid 90s (highest in the urban areas around Chicago) each afternoon through at least Thursday. When combined with surface dewpoints in the low to mid 70s, heat indices will again top out in the 100-105 degree range (locally in excess of 105) both Wednesday and Thursday. Meanwhile, expect very warm overnight temperatures, with readings likely struggling to fall out of the low 80s in the city tonight and again Wednesday night. While such readings are not necessarily uncommon to experience on a day in the middle of summer in our area, it is less common to experience such conditions on 4+ straight days with little to no relief. It is thus the cumulative effects of the heat that is most concerning with this heat, and not necessarily the peak temperatures and heat indices on an individual day. Therefore, no changes are planned to going heat headlines currently in effect.

Wednesday, and much of Thursday, waves of severe thunderstorms will continue to be favored northwest of our area (from the Plains northeastward through the Upper Midwest) within a belt of active west-southwesterly upper-level flow residing along the west-northwestern periphery of the upper-ridge. However, as the upper ridge begins to expand eastward, it will allow this active belt of westerly upper-level flow to shift into our area late in the week. Accordingly, while our area will get relief from the extreme heat this weekend, it will come at the price of increasing chances for showers and thunderstorms. While it will not be raining and storming constantly, it appears we may end up with a couple of waves of showers and thunderstorms during the holiday weekend, most notably late Friday and on Saturday. Some of these storms could be severe and produce torrential downpours.

KJB

AVIATION /00Z TAFS THROUGH 06Z THURSDAY/

Issued at 616 PM CDT Tue Jun 30 2026

Forecast concern for the terminals...

- Breezy southwest winds early this evening then again Wednesday afternoon with gusts around 25-30 kts.

A broad area of high pressure continues to reside over the eastern CONUS which will allow mostly clear VFR skies and hot conditions to prevail through the TAF period. However, there is a non-zero chance (10-15%) for a few MVFR clouds (bases around 2000-2500 ft) to develop late tonight into Wednesday morning. Given the low confidence on the coverage and duration of these lower clouds have opted to maintain the SCT020 in the TAFs for now.

Otherwise, the main forecast item of note will be the breezy southwest winds gusting around 25-30 kts early this evening and again Wednesday afternoon. While gusts will ease overnight, some occasional 15-17 kt gusts will be possible at times tonight and again Wednesday night.

Yack

CLIMATE

Issued at 1249 AM CDT Tue Jun 30 2026

.Daily Records for the Upcoming Week........

Chicago (KORD) Record High Record Warm Minimum June 30 99 (1953) 80 (2018) July 1 103 (1956) 78 (1931) July 2 99 (1970) 79 (1911) July 3 102 (1949) 78 (1911) July 4 102 (2012) 80 (1921)

Rockford (KRFD) Record High Record Warm Minimum June 30 102 (1931) 76 (2018) July 1 101 (1931) 76 (1970) July 2 99 (1910) 74 (1970) July 3 99 (1925) 75 (2012) July 4 102 (2012) 77 (1977)

NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...Extreme Heat Warning until midnight CDT Thursday night for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012- ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039- ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Extreme Heat Warning until midnight CDT /1 AM EDT/ Thursday night for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 9 PM CDT this evening for Winthrop Harbor IL to Gary IN.