The predicted huge north to south temp spread Wednesday has materialized as the Chicago area finds itself divided between warm southerly winds south of a warm front headed toward the city—and the chilly southeast winds coming off 44-deg Lake Michigan waters.
At mid afternoon—temps varied 35 degrees from 41-deg at Waukegan Harbor to 76 degrees (and still rising) south of Chicago in Peotone and Roselawn, IN.
Clusters of t-storms have dotted sections of Illinois and Wisconsin—but have avoided Chicago proper as of post time. Hail described as ping ping to golf ball size has rained down on sections of downstate and far northwest Illinois and southern Wisconsin.
Temperatures will rise in Chicago tonight as a northbound warm front passes ushering tropical air from the Gulf of Mexico into the area. That air mass has generated temps as warm as 84 on the University of Illinois campus in Champaign/Urbana and 88-deg in downstate Terre Haute, Indiana.
Spotty t-storms can’t be ruled out overnight into Thursday morning—impacting perhaps 20 to 30% of the area as the warm air moves in. But it’s in the warmer hours of Thursday and Thursday evening t-storm numbers are likely to increase. Modeling, which isn’t always perfect in laying our t-storm coverage—but offer a guide which is interesting to follow—suggest a cluster of more numerous storms could impact some parts of the Chicago area toward lunchtime Thursday and in the hour or two after—but suggests the greatest coverage of showers and t-storms may occur in and around Chicago in the 4 to 10 pm time frame Thursday.
There’s to be a jet stream overhead and moderate levels of instability—enough to perhaps lead to a few heavier t-storms which could warrant monitoring. Atmospheric profiles off our models are not extreme Thursday afternoon despite the warmth, the availability of moisture and convergence of low level winds with an approaching cold front. Still, with strong winds aloft, any storms which develop have the potential of reaching up into the strong upper wind field and mixing some of the wind energy down to the surface in the form of some vigorous storm gusts. And recent t-storms with this spring storm system have a history of hail production. So the Storm Prediction Center is assessing a ‘MARGINAL SEVERE WEATHER RISK” later Thursday into Thu evening—a Level “1” risk on the 5-level SPC severe weather scale.
A prolonged “Below normal temp” regime appears to be coming together this weekend through next week and into the week which follows. Temps this week will average a degree below normal—but may come on closer to 7-deg below normal next week.
HERE’S MY WED CHICAGO METRO FORECAST (4/19/2023):
TONIGHT: Partly cloudy and turning warmer. A few t-storms are possible—but likely to impact only 20 to 30% of the metro area. Temps will rise into the mid to upper 60s late as southeast wind shift south/southwesterly away from Lake Michigan’s chilly water.
THURSDAY: Partly cloudy, fairly windy and warmer. A shower or t-storm is possible in the morning and in parts of the area around lunchtime. But more numerous showers and t-storms may sweep as much as 70% of the area in the 4pm to 10pm time frame Thursday afternoon and evening. High 76.
THURSDAY NIGHT: Showers and t-storms exit—then cloudy spells and cooler. Low 49.
FRIDAY: Clouds breaks allow mixed sunshine, turning breezy and not quite as warm. High 65.
SATURDAY and SUNDAY: Cloudy spells—but with a bit of mixed sun, windy and cooler. High Saturday 52. Sunday’s high 48.
MONDAY: Increasing cloudiness and cool. Winds off Lake Michigan. High 55—but 40s lakeshore
TUESDAY and WEDNESDAY: A good deal of cloudiness, cool and breezy. A few sprinkles possible. Chances for some rain increase Wednesday. High Tuesday 57—Wednesday’s high 55—but cooler 40s each day along Lake Michigan.