textproduct: Chicago

KEY MESSAGES

- Hot and humid conditions will continue into the holiday weekend, with peak heat index values around 105 degrees today and around 100 degrees Friday and Independence Day.

- Waves of thunderstorms are expected through the weekend. With that said, there will be many dry hours. Any thunderstorms on Friday will be capable of producing damaging winds.

DISCUSSION

Issued at 300 AM CDT Thu Jul 2 2026

Hot and humid conditions will persist today, and possibly over some or all of the forecast area on Friday. Slight mixing of dew points across a weakening cap today should keep dew points in the low to possibly mid 70s. With temps expected to peak in the low to mid 90s, today will feature another afternoon with heat index values in the 100 to 105 degree range. Maintained the current Extreme Heat Warning through this evening, though some consideration of an extension through Friday will be needed for at least the southern half of the forecast area depending on the expected outcome of convection tonight into Friday morning.

As of 3AM, elevated convection continues to develop across central Wisconsin along a generally WSW to ENE corridor. Remaining capping farther south has resulted in a notable southern terminus of the convection from the northern Milwaukee metro to far northeast Iowa. A resultant outflow has started to show some slowing with its southward trek toward the state line, but should shift far enough south to disrupt the low-level wind field for a few hours across the northern tier of counties in northern Illinois early this morning. With recent convection struggling to extend farther south, concerns for new convection along this outflow boundary are waning with time. However, have maintained a slight chance of showers and storms over these northern counties through mid-morning.

Under the expectation that little to no convection occurs over northern Illinois through the daytime hours, the first favored window for storms will be very late this evening into the overnight hours. A mid-level wave emanating from eastern Colorado early this morning as evident by WV imagery and associated downstream convection may go through a couple iterations of convective enhancement over the next 24 hours as it tracks toward central Wisconsin through this evening. It appears likely that a (potentially) organized cluster of convection will develop somewhere around the NE/IA line by early evening and focus along a residual outflow from current convection. With the ongoing de-amplification of the mid-level ridge and substantially less capping over the area by this evening, any well formed MCS could survive into southern Wisconsin and northern Illinois late this evening into the overnight hours. However, convection would likely become cold pool dominant with southward extent as stronger shear/mid-level flow remain farther north over Wisconsin. With that said, a stronger cold pool surging into the antecedent warm and humid airmass implies a potential for strong to locally damaging winds into portions of northern Illinois.

A more potent wave currently crossing northern Arizona will become another focus for convection over our area on Friday. This wave will cross southern Wisconsin mid to late afternoon, setting the stage for a potential line of convection in the area later Friday afternoon into the evening. If convection materializes tonight, there will likely be a notable outflow boundary stalled over the forecast area Friday morning that could complicate the forecast by altering the location of convective initiation. Meanwhile, no convection tonight would lead to a fairly untapped and uncapped airmass over the area through the entire day. While these differences introduce a decent amount of uncertainty regarding the timing and location of convection, late afternoon through mid-evening Friday appear to have the greatest chance for at least a broken line of storms over northern Illinois and northern Indiana. Modest deep layer shear and an inherent high DCAPE reservoir with the warm/humid airmass support the risk for damaging winds with any linear segment or multicell clusters.

A mid-level impulse exiting the northern Rockies late on Friday will provide renewed convective episodes in the region as the mid-level pattern becomes zonal. The track of this convection will likely focus along an effective cold front produced by the combined effects of convection over the next 48 hours. So while convection seems likely in the region on Saturday/Independence Day, the location of convection could range from southern Wisconsin to southern Illinois. Furthermore, with forecast guidance consistently depicting a slowing or stalling mid-level wave over the western Great Lakes late Saturday into early next week, timing out precip chances becomes even more difficult if not impossible.

As the aforementioned wave eventually drifts eastward, drier and somewhat cooler conditions are expected by the middle of next week.

Kluber

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 648 AM CDT Thu Jul 2 2026

Decaying convection over southern Wisconsin this morning has pushed a stout outflow boundary southward toward the terminals, with a N/NNE wind shift and brief gusts to 20 knots affecting all terminals by 13Z. A band of BKN MVFR ceilings will also trail the outflow boundary for an hour or two. Precip is not expected to affect the terminals, though a couple SHRA could near ORD/DPA to the north through mid morning.

VFR conditions will prevail late this morning through sunset. N/NNE winds associated with the outflow are expected to veer SW with gusts over 20 knots by late morning. SW winds around 10 knots should then persist tonight through Friday morning.

A mid-level wave over western Nebraska and Kansas this morning is expected to generate a cluster of TS over the Missouri River Valley by early evening. This cluster of TS may track across southern Wisconsin and perhaps well into northern Illinois very late this evening and especially overnight. Gusty winds could accompany any TS. Additionally, any substantial coverage of TS would disrupt the low-level wind field and yield VRB, or more likely, winds with an easterly component toward daybreak Friday.

Kluber

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

Chicago (KORD) Record High Record Warm Minimum 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 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 tonight 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/ tonight for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.