Chilly weekend (by April standards) ahead in Chicago.

This weekend’s temps are to average 22-deg cooler than last with daytime highs both Saturday and Sunday remaining in the 40s—something which 153 years of weather records indicated has happened in only 16% of days at this point in an April.

The air aloft is cold—and therefore unstable. That means any daytime heating will encourage clouds and scattered “instability” showers to form. This should occur in the late morning and afternoon hours. So both Saturday & Saturday should begin with a fair amount of mixed sun only to see more widespread cloudiness to begin developing as daytime temps rise.

To put Saturday’s predicted temps here in perspective—the normal high and low on March 17 are 48 and 31-degrees. The forecast Saturday in Chicago is for a high of 47 and a low of 31—practically identical! That means our temps Saturday, April 22 will approximate the normal temps a month earlier on March 17.

And the cool pattern is to linger—likely through next week and into the week that follows, which is when May2023 gets underway. Temps are to come in 3-deg below normal this week—but will average more than 8-deg below normal next week and 2-deg below normal in the week which follows—though modeling hints warming may take hold later in the 2nd week.

The reason for the persistence of the cool air is another rex block—similar to the blocking pattern which held unseasonably warm air over the Midwest last week. This time, however, the sluggish movement of weather systems encouraged by the developing blocking pattern will trap cool air over us.

What’s more—a series of storms passing across the Deep South will combine with high pressure centered over Canada to produce prevailing easterly winds virtually all of next week off Lake Michigan which is currently only 45-deg—further reinforcing the cooler than normal temps we’re predicting.

HERE’S MY LATEST FRIDAY CHICAGO METRO FORECAST (4/21/2023)

TONIGHT: Scattered clouds and chilly. Initially gusty winds ease slowly overnight. Low 37—but in the low 30s cooler inland locations.

SATURDAY and SUNDAY: Both days open with a fair amount of sun and only patchy clouds. But clouds will build with daytime heating a spotty light showers impacting 20 to 30% of the area at any given time are possible in the late mornings and afternoon. A few ice pellets may be mixed in. Clouds scattered and cold Saturday night. High Saturday 47. Sunday’s high 46.

MONDAY through THURSDAY: Partly cloudy, breezy by day and cool through the period. East winds off Lake Michigan will lead to the coolest daytime highs along Lake Michigan. Daily highs in the mid 50s. Lows at night in the low to mid 30s—but chillier inland (local mid to upper 20s there).

FRIDAY: More clouds with time, continued cool. Growing prospects for some rain later in the day—but more likely at night. High 60—but upper 40s or low 50s along Lake Michigan.