textproduct: Chicago

KEY MESSAGES

- Heat wave expected to continue through at least Thursday, potentially extending into Friday depending coverage of storms and cloudiness.

- While not a complete wash out, thunderstorm chances increase Thursday night, with at least 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 147 AM CDT Wed Jul 1 2026

Strong mid-upper level ridge of high pressure will change very little through Thursday providing for a continuation of our hot and humid conditions. By later Thursday this ridge will begin to slowly weaken and shift eastward. This will allow for the active ring of fire pattern that has been providing for waves of severe thunderstorms from the central Plains into the Upper Great Lakes to gradually shift southward in our area by week's end and through the holiday weekend.

No changes planned or needed for the current Extreme Heat Warning. Today will be another hot and humid day with conditions pretty similar to Tuesday expected. The NAM, which has been on the upper end of the guidance spectrum with dewpoints, has generally been verifying best. For this reason, leaned pretty heavily on the NAM which has Tds in the mid to locally upper 70s this afternoon, generally 2-4F lower than Tuesday. Forecast soundings depict a continued strong subsidence inversion limiting the depth of mixing, so it is possible that dewpoints end up a bit higher, but with all guidance generally depicts lower Tds today vs Tuesday. Temperature should again climb into the lower to middle 90s, hottest in the Chicago urban heat island. Heat indices should once again climb into the 100 to locally 110 degree range this afternoon.

Convection and especially convective outflow is likely to get nearer to or even into our northern CWA late tonight into early Thursday morning. Guidance generally suggests that capping should be sufficient to keep most of the effects of this convection north of our area Thursday allowing for another hot and humid afternoon Thursday.

By Thursday night, it appears that the ridge should have weakened/shifted sufficiently east to at least open the door to the potential for MCS activity to meander into our CWA. Timing of the very low amplitude synoptic disturbances that ultimately serve as the impetus for MCS development is often difficult to impossible at this distance. Depending on where/if an MCS tracks across the general region Thursday night/Friday time frame will play a pivotal role in temperatures for Friday. If (and where) convection and/or lingering effects from convection (cloud cover, cold pool, etc) aren't a significant factor, then Friday has the potential to be a 5th day with heat indices above 100 degrees. Certainly plausible that heat headlines may need to be extended into Friday for some portions of the area, but confidence is far too low to make any such change on this shift.

Over the upcoming holiday weekend, certainly plausible that there could be one or two additional rounds of showers and thunderstorms. The weekend most certainly does not look like it will be a wash out, but one or two convectively enhanced shortwaves could lead to convection in the area pretty much at any point in time over the weekend. As the upper ridge weakens, a subsequent relaxing of the geopotential height gradient on its northern flank is likely to result in a weakening of the mid and upper level flow. This should lessen the threat of significant severe weather this weekend, though a stronger MCV could certainly lead to a more localized greater severe threat this weekend. A very moist air mass will remain in the area, setting the stage for very heavy rainfall production with stronger storms. Given the low confidence in timing/track of MCVs this weekend, made no changes to the NBM pops which at first glance appear very high, but important to note they just reflect the chance of a hundredth of an inch of rain in a 12 hour period.

- Izzi

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 621 AM CDT Wed Jul 1 2026

Low-end VFR visibility from HZ will persist for a few hours. A FEW MVFR stratocumulus are also expected as the boundary layer rises with daytime heating this morning. Otherwise, VFR conditions are expected through the period.

SW winds will gust up to around 20 knots through early afternoon, then increase with gusts over 25 knots mid afternoon through sunset. Expect winds to settle around 10 knots tonight, then gust again to around 20 knots Thursday morning.

Will need to closely monitor the evolution of upstream convection to the northwest tonight, with expectations for a line of storms extending from near Omaha to northern Wisconsin early this evening to shift southeast while decaying through the night. While the chance for TSRA at the terminals is below 20 percent, there is a higher chance (30 percent) that a remnant outflow boundary surges southward and crosses northern Illinois toward sunrise Thursday. If this occurs, winds at all terminals would likely turn N/NNE and gust over 20 knots for a couple hours before gradually veering SW by late morning.

Kluber

CLIMATE

Issued at 1246 AM CDT Wed Jul 1 2026

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

Chicago (KORD) Record High Record Warm Minimum 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 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...None.