Chicago area humidities to rise in coming days; inland warmth and cooling lake breezes to hold through coming weekend

AIR QUALITY ISSUES

Air quality issues have arisen as we move into the 5th day of an atmospheric blocking pattern which slows weather movement. Lake breezes further trap pollutants, including daytime and evening ozone and particles—a 30+ degree temp spread continued between the lakeshore and inland areas. There will be 50s on the immediate shoreline and mid to upper 80s inland—temps to flirt with 90 in coming days. Humidities to creep high leading to modest isolated t-storm chances, but little chance of significant drought relief.

ATMOSPHERIC BLOCKING PATTERN

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.