It’s been a warm one over all but immediate shoreline locations. Check out the spread in temperatures. 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, IN
  • 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, IN

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

  • It should be noted that Lake Michigan water temps were averaging 54 degrees over southern Lake Michigan, even though one of Chicago’s beaches reported the first 60-degree 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 which 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 feet 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 feet of the atmosphere, which means 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 evening 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 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 degrees 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 Wednesday, Thursday and Friday 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 minutes. And days will continue slowly lengthening through June 21st with the pick up of an additional 17 minutes of daylight.