Sharp cooling hits with the passage of a PNEUMONIA FRONT—so named because of the jarring temp changes such fronts produce. This front is dropping southward and will pass the area taking temps down from afternoon highs in the low 80s to the low and mid 50s by 9 and 10pm.  

Such fronts sweep “NNE” winds into Chicago—winds which have traveled the length of Lake Michigan over chilly water. That helps drive the sharp temp drops they produce—in the case of Tuesday evening’s front, a drop of 20 to 30-deg in a matter of hours—between 6 and 9 p.m.

A COOL, SUNNY WEDNESDAY IS AHEAD—but smoke of Canadian wildfires is settling into the area ALOFT. This will lend the sky a hazy orangish hue.  

Temps will be CHILLY WEDNESDAY—limited to the low and mid 60s inland and to the 50s at the lake.

Temps come back closer to seasonal norms (i.e. low 70-deg highs and upper 40 to low 50-deg lows) the remainder of this work week and over the coming weekend.

SIGNIFICANT WARMING is indicated next week, the weekend which follows and into the following week. Temps next week will average more than 10-deg warmer than this week—which is a BIG CHANGE. Daytime highs appear, from this distance in time, likely to reach the 80s over much of the area from Tuesday forward next week.

Full forecast details and more at the WGN Weather Center blog

TONIGHT: Turning breezy and sharply cooler. Scattered clouds with north/northeast winds taking hold. Low 47.

WEDNESDAY: Sunny and cool for the season with a hazy sky due to smoke aloft off Canadian wildfires.  High 63—but 50s lakeshore.  (Note: Areas well inland are likely to see mid to upper 60s.)

WEDNESDAY NIGHT: Mainly clear, chilly by May standards. Low 43—with some upper 30s cooler inland locations.

THURSDAY: Mostly sunny and milder. High 76—but mid 60s immediate lakeshore and on area beaches.

FRIDAY: More clouds, mild. Scattered showers—some possibly thundery. High 70—but cooler along Lake Michigan.

SATURDAY: Mostly sunny, near seasonable temperatures. High 73.

SUNDAY: Partly cloudy, turning cooler along Lake Michigan late in the day. High 74—but dropping off as northeast winds lock in late in the day.

MONDAY: A good deal of sunshine. Mild inland—but with cooling breezes along Lake Michigan. High 78—but low to mid 60s on area beaches. 

TUESDAY: Partly sunny and warmer. High 81—but mid 60s to low 70s beaches and lakeshore.