Marine Weather and Tide Forecast for Gurnee, IL

DISCUSSION
Issued at 248 AM CDT Wed Aug 5 2026

Broad aggregate mid and upper-level troughing over the north central CONUS will steer a few smaller scale impulses across our area, resulting in a few clusters of showers and thunderstorms across the region today into tonight. One such wave is currently driving a line of heavy rain producing showers and storms eastward across northern IL. Fortunately, the eastward movement ~25 mph is limiting the duration of heavy rainfall at any given location, thus limiting the flash flood threat, at least in the near term. Nevertheless, a quick localized inch of rain may fall under the strongest cores.

Following this initial line of showers and storms, we will be monitoring the trends with the ongoing cluster of storms over IA. A good amount of available guidance suggests that this activity will track eastward into northwestern IL around daybreak. Thereafter, it remains a bit unclear as to how long it may hold together as it moves into northeastern IL (especially north of I-80) during the mid-morning hours, owing to the poor diurnal timing and modest instability. Nevertheless, the current thinking is that there will at least be a region of weakening showers moving into the Chicago metro area (mainly in the 8-11 am timeframe). Should this activity hold together into northeastern IL this morning, the presence of deep rich moisture (precipitable water values nearly to 2") will support locally heavy downpours.

After a break in the shower activity this afternoon, another round of developing convection is probable near the surface frontal boundary late this afternoon and evening in response to the approach of the next mid-level impulse. However, with diurnal destabilization expected to remain limited across far northern IL (especially north of I-88 where temperatures will stay in the 70s) as a result of persistent cloud cover through the afternoon, the main focus for stronger convection will likely end up south of I-80. This thinking continues to match the SPC's current Day 1 outlook, which indicates a level 1 of 5 severe threat into west central IL. The main threat with any stronger storms would be locally strong damaging wind gusts and locally heavy rainfall, particularly associated with any strong storm clusters. The overall threat of flash flooding will ultimately be dependent upon if and where multiple storms to move over the same areas (training). While this possibility cannot be ruled out on a localized basis in parts of our area, the better potential for this may end up remaining south- southwest of our area.

The focus for active weather should largely shift south of the area for Thursday and Friday. However, active weather (with shower and thunderstorm chances) is likely to return eighter this weekend, or early next week.

KJB

Weekend onward:

As aggregate upper-level troughing shifts eastward toward the end of the week, a quasi-zonal to northwesterly upper-level flow pattern will materialize across the Upper Great Lakes region supporting additional waves of showers and storms. Some of these may be rambunctious as the eastern edge of an EML plume is repeatedly re-advected eastward atop a stalled frontal boundary draped across the Great Lakes. Naturally, confidence in when/where eventual thunderstorm clusters will roam is low at this range. With that said, the pattern matches conceptual models for threats for severe weather and flash flooding in the general region this weekend into early next week.

Borchardt/KJB

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/
Issued at 1222 PM CDT Wed Aug 5 2026

A frontal boundary is expected to stall over the airspace this afternoon leading to periods of showers and worsening visbys/cigs.

First off, a few thunderstorms may develop in the next few hours directly over DPA/ORD/MDW/GYY as a lead wave interacts with the warm and humid environment. Will cover this threat with PROB30s with expectation for coverage to end up highest over Lake Michigan. Later this afternoon, the area of showers and storms over southern Iowa will slide eastward. Coverage of thunder with the second round may be less owing to less instability, though still expect at least -SHRA to move over all but RFD favoring the 22-02Z time window. Forecast confidence for thunder remains lower than average.

After sunset, showers may continue to fester along the stalled frontal boundary across the area. So, will maintain the inherited VCSH through the overnight hours. Calm winds and abundant moisture should allow for cigs to build downward into MVFR and IFR through the night especially away from Lake Michigan. Areas of fog may develop as well. The inherited TAFs handle such an idea well, though further adjustments downward may be needed by the 00Z TAF set.

Improvement in cigs/visbys may be slow tomorrow morning though a general trend upward is expected from mid-morning through early afternoon seems reasonable. With the frontal boundary still in the neighborhood, cannot rule out a shower or thunderstorm in the airspace through the afternoon hours.

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...None.