Harvey, IL 60426 Weather

Key Messages

- Locally dense fog across portions of far northeast Illinois this morning, primarily Lake County.

- Dry and unseasonably mild weather will continue through the upcoming weekend.

Discussion

Issued at 245 AM CDT Fri Oct 23 2026

Conditions are largely quiet to kick off our Friday. The area sits beneath clear skies while temperatures have fallen into the 40s; still hanging out in the 50s in the city. A bank of dense fog crept into northern Lake Co last evening and has been very gradually expanding south and west. As of 2:30 AM, dense fog coverage remains confined to northeastern portions of the county and up near then WI state line. Accordingly, we made the decision to issue a Dense Fog Advisory for Lake County, IL through 9 AM. It's possible by daybreak that pockets of dense fog expand into portions of McHenry and northern Cook counties. Elsewhere, several sites around the CWA are reporting 3 to 5 mile visibilities as dewpoint depressions continue to drop. Outside of the aforementioned areas, such visibilities will remain possible around the CWA through dawn with the primary dense fog concerns in our northeast, but can't rule out some pockets of denser fog farther west and south. Any fog should burn off by mid- morning at the latest.

Surface high pressure and low level ridge axis will slide to our east today bringing light southerly winds and more mostly sunny skies. Temperatures will again be very comfortable for late October with highs forecast in the lower and middle 70s; maybe stuck in the upper 60s near the lakeshore. Similar temperatures are expected through the weekend with a good mix of clouds and sunshine. The prominent surface high will continue to keep the rain away as it scoots east across the Great Lakes.

A cold front will work into the upper Midwest and provide some upstream rain chances over the weekend. However, the front appears to lose a lot of its luster before moving across the area late Sunday into Monday and the better layer moisture is progged to get locked up to our north, so ultimately not expecting rain in our local area early next week. This front even looks to lift back north across our area again as a warm front in the Tuesday to Wednesday window, but again with no rain in the forecast. Next appreciable opportunity for rain may be with the trailing cold front Thursday into Friday, but of course, much uncertainty with this. In the meantime, expect warmer-than-normal conditions to continue with 60s and lower 70s favored next week.

Doom

Aviation

Issued at 105 AM CDT Fri Oct 23 2026

The only aviation weather concern continues to center the dense fog threat in and near the Chicago terminals early this morning.

A surface high pressure ridge axis over the western Great Lakes will continue to slide eastward today. As it does, variable to nearly calm surface winds early this morning will become light (4-7kt) from an east-southeasterly direction.

The main question that remains is how far south the area of ongoing dense fog is able to develop into northeastern IL prior to daybreak this morning. Through Thursday evening, an area of dense fog has persisted across the western shore of Lake Michigan, particularly across eastern/southeastern WI, with the southward extent reaching KUGN in far northeast IL. Interestingly, satellite trends over the past couple hours suggest very little southward push to this point, possibly as a result of the light low-level flow beginning to turn to a less favorable east-southeasterly direction. Accordingly, there remains uncertainty with the extent of fog at the main Chicago terminals early this morning. Nevertheless, we did not make any major changes for the 06Z TAFs as it remains possible for some patchy areas of shallow ground fog to develop for a couple hours around daybreak.

Fortunately, any fog that does develop will burn off rather quickly after sunrise. Accordingly, VFR conditions are expected to quickly return and persist through the remainder of the forecast period.

KJB

Lot Watches

IL...Dense Fog Advisory until 9 AM CDT this morning for ILZ006.

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