—Good Memorial Day all! It’s been a warm one over all but immediate shoreline locations. Check out the spread in temps.

–AN AIR QUALITY ALERT HAS BEEN DECLARED THROUGH TUESDAY BY THE ILLINOIS EPA into Tuesday night and it wouldn’t be surprising to see this extended deeper into the coming week. The air mass stalled over us is growing a bit “dirty”. More on that to come.

AMONG THE WARMER READINGS at mid-afternoon Memorial Day (Monday) across the Chicago area:

  • 88 Oswego
  • 87 Joliet
  • 86 Montgomery
  • 86 Plainfield
  • 86 Peotone
  • 86 Poplar Grove
  • 85 Lake Barrington
  • 85 Hebron, Indiana
  • 85 Geneva
  • 84 Kankakee

ON THE IMMEDIATE LAKE MICHIGAN SHORELINE at mid-afternoon Memorial Day (Monday):

  • 56 Waukegan Harbor
  • 56 Winthrop Harbor
  • 56 Wilmette buoy
  • 57 Harrison-Dever Crib (3 miles off Chicago’s North Side)
  • 59 Michigan City, IN buoy
  • 63 Calumet Harbor
  • 63 Burns Harbor, Indiana

That’s as much as a 32-deg spread across the Greater Chicago area. But the coverage of the coolest temps was literally ON THE IMMEDIATE SHORELINE.

–It should be noted too that Lake Michigan water temps were averaging 54-deg over southern Lake Michigan even though one of Chicago’s beaches reported the first 60-deg water temp of 2023. Those readings are CHILLY for swimming, to say the least.

–We’ve entered the 5th day of an atmospheric blocking pattern that slows weather system movement. The result is, the air mass is starting to get a bit “dirty”–with elevated levels of particulates and afternoon ozone creating MODERATE AIR QUALITY. Levels of pollutants are even being tagged as “UNHEALTHY FOR SENSITIVE GROUPS”. Further complicating the air quality situation are the lake breezes cooling the lake shore. These bring a fairly shallow layer of cool air into shoreline locations—not much more than 2,000 ft. deep. Temp inversions shut down the mixing of air which usually occurs and which thins air pollutants by mixing through a deeper layer of the atmosphere. These lake breezes are to continue all week so air quality issues will continue.

–A look at winds through the atmosphere shows wind speeds less than 10 mph from ground level up through the lowest 5,000 ft. of the atmosphere which means the there really isn’t the kind of circulation to MIX OUT pollutants. Instead, they are just suspended with daytime sunlight leading to the photochemicial reactions which produce afternoon and early even ozone as a by-product. LITTLE CHANGE IS EXPECTED in this light wind regime this work week until afternoon winds pick up Friday and better organized “NE” winds on the southern flank of a southbound early meteorological summer high pressure being to bring some mixing of the air back onto the scene in Chicago this weekend into early next week.

–Coming days will continue to see a wide range in temps between the lakeshore and inland locations with temps Tuesday, Wednesday and possibly Thursday flirting with if not topping 90-deg in warmer inland locations even as 60 and low 70s reign supreme in the Lake Michigan shoreline.

–The area will see more haze as humidities creep higher this week with dew points reaching the low to mid 60s inland. Very modest isolated t-storm prospects are noted in the Wed, Thu & Fri time frame—but there is little prospect for serious relief from the developing FLASH DROUGHT SITUATION in the area. Chicago O’Hare rainfall for May continues at 0.42″ which is now down to 10% the normal rain—and May 2023 continues on track to finish the 2nd driest May of the past 153 years.

–THE RATE AT WHICH DAYS ARE LENGTHENING IS SLOWING as we approach the longest day of 2023 in the northern hemisphere which will occur with the summer solstice on Wednesday June 21st—just 24 days from now. Chicagoans have seen the hours of daylight since our shortest day back on Dec. 21 increase by 5 hours and 39 mins. And days will continue slowly lengthening through June 21st with the pick up of an additional 17 minutes of daylight.



TONIGHT: Partly cloudy with light winds, some haze—and near seasonable temps. Low 58—low 50s cooler inland locations.

TUESDAY THROUGH THURSDAY: Partly sunny and hazy with a modest increase in humidity in coming days. Quite warm to hot afternoons inland—but lake breezes will continue to cool beaches and shoreline locations. Slight chance for a few low coverage, isolated t-storms Wednesday and Thursday afternoons—but likely impacting no more than 15 to 20% of the area. High Tuesday and Wednesday 91; Thursday’s high 89. Lakeshore and beach highs mainly mid 60s to low 70s. Nighttime lows all nights and early morning in the mid 60s.

FRIDAY: Mostly sunny, still warm but with better organized afternoon lake winds. High 88—but 60s lakeshore.

SATURDAY and SUNDAY: Partly cloudy, a bit breezy and not as warm—especially lakeshore areas. Highs Saturday 80—but closer to 75 Sunday—with beach and lakeshore highs from the mid 50s to low 60s.

MONDAY: Mixed sun at the open but clouding over in the afternoon. Chance of some showers at night. High 86—but mid 60s to near 70 lakeshore.