textproduct: Chicago

KEY MESSAGES

- The next chance of showers and thunderstorms is with a cold front moving across the area midweek.

DISCUSSION

Issued at 135 PM CDT Sun Aug 23 2026

The weather pattern across the country for the next week looks to be dominated by a western ridge with troughing over the Great Lakes and Northeast. This leaves our area in northwest flow with pleasant temperatures and generally below average precipitation.

Surface high pressure will settle into middle Mississippi Valley and western Great Lakes tonight through Monday night. This will result in light/calm winds, low dewpoints, and seasonable temperatures. Once diurnal cumulus dissipates this evening, skies should be clear tonight. The clear skies, low dewpoints, and calm winds should allow for strong radiational cooling. Low temperatures tonight should drop into the 50s, coolest away from the urban heat island where some of the typically colder spots could even dip into the upper 40s. While the boundary layer is dry, the nearly ideal radiational cooling set- up could allow for some areas of ground fog late tonight into early Monday morning, especially the typically fog favored low lying and cold air drainage areas.

Monday should be a near carbon copy of today, but with less wind. In fact, not much change in the weather is expected through Tuesday. Later Tuesday into Tuesday night the longwave trough over the Great Lakes is expected to scoot off to the east, but fast on its heels looks to be another shortwave which will help reestablish the long wave trough over the Great Lakes and Northeast. A cold front associated with that next shortwave trough is progged to move across the area sometime Wednesday or Wednesday night. A frontal boundary stalled out across the Gulf States should limit moisture return in advance of this cold front. Despite somewhat marginal moisture return, fairly strong forcing and cooling temps aloft with the approaching upper trough could support some showers/storms when the front moves across the region sometime around Wednesday timeframe. Frontal timing could also play a role in coverage of showers and storms, if the front were to move through at a less diurnally favorable time, that would result in lower storm chances and rainfall amounts.

In the wake of the front, another period of sunshine and seasonable temperatures with comfortable humidity looks to be on tap Thursday into Friday. There are some indications the long wave pattern across the CONUS could turn more zonal and potentially lead to more rain chances into next weekend, but that is still far out and confidence not terribly high.

- Izzi

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1241 PM CDT Sun Aug 23 2026

Key messages for the 18Z TAF period:

* A lake breeze will bring light and variable winds to MDW and GYY this evening and overnight

* Another lake breeze will turn NW winds to E in Chicago Monday afternoon

NE winds around 10 to 12 kt will remain through the afternoon with occasional gusts as high as 20 kt. Winds will go light for this evening. A lake breeze is expected to pass through MDW and GYY this evening. While magnitude will be light, direction will vary through the night and into early Monday. Elsewhere, NW is favored tonight. Expect NW Monday morning going ENE at Chicago sites in the mid-late afternoon with the passage of another lake breeze. Expect VFR throughout the period.

Doom

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Beach Hazards Statement until 10 PM CDT this evening for INZ002.

LM...None.