The heavens opened overnight and today over the southern suburbs.  While rainfall were modest in the city, totaling 0.21″ at O’Hare and 0.42″ at Midway, RAINFALLS WERE HEAVY FARTHER SOUTH.

2.40″ fell at Valparaiso—while 1.95″ came down at Kouts, 1.65″ at Hebron, 1.63″ at Chesterton, 1.59″ at Roselawn and 1.60″ at Dyer—all in Indiana. Other Indiana totals included 0.95″ at Crown Point, 0.91″ at Munster, 0.89″ at Portage and 0.85″ at Ogden Dunes—again ALL in Indiana. 

At the same time, Grant Park in Kankakee county recorded 1.67″ while 0.80″ was recorded at Chicago Heights, 0.79″ at South Holland, 0.66″ Elmhurst and 0.59″ at Oak Brook. AMOUNTS TAPERED OFF dramatically farther north with only 0.07″ recorded at Woodstock, 0.03″ at Vernon Hills and just 0.02″ at Libertyville.

THE PREDICTED DOWNWARD CYCLE IN TEMPS is underway.  Thursday’s 71-deg high at O’Hare was down 13-deg from Wednesday’s 84—and further erosion in temps is expected a strong northwest flow at the jet stream level out of northwest Canada’s Yukon Territory is to send temps even lower.

All or parts of 7 states—from the Dakotas south to Colorado and east into western Iowa are under FROST AND FREEZE ADVISORIES in coming night.

Northwest winds have been howling at ground level as the chilly air invades across the Plains and western Midwest.  And the strong wind regime is to build eastward into the Chicago area with brisk overnight winds averaging 8 to 18 mph and gusty building to 14 to 30 mph with gusts in the 30 to 35 mph range Friday.

THE COOLEST AIR IN 5 MONTHS (since early May)  is sweeping into the Chicago area. While highs will reach into the low 60s here Friday—a further 10-deg decline over what we saw today in the city—weekend highs are to remain in the mid 50s with nighttime lows in the 40s and scattered 30s aren’t out of the question inland.

The incoming air is quite “unstable”–in other words, very cool aloft. When that happens, air is encourage to rise with any level of daytime heating and this produces cloud and scattered shower development. So while skies are to clear a great deal overnight and the day is to open with sun, clouds should assemble expeditiously Friday and again after some initial sunshine both Saturday and Sunday.  And while rain chances are lower west of Lake Michigan over the weekend, a spotty shower is possible—and some lake effect clouds and rain showers are to sweep into sections of the Northwest Indiana and Lower Michigan lake-effect belt.

THIS WEEKEND is to end up 20-deg or more cooler than last weekend.

And the chill is to carry into early next week as another blocking pattern sets up aloft, effectively trapping the cooler than normal temps over Chicago.  Brief mid week “warming” may segue into a cloudy, potentially rainy weather regime next Thursday and Friday—with a cool weekend to follow later next week.

HERE’S MY LATEST THURSDAY CHICAGO METRO FORCAST (10/5/2023):

TONIGHT: Clearing, breezy and noticeably cooler. Low 51—but mid 40s cooler inland locations.

FRIDAY: WINDY AND STILL COOLER.  The day opens sunny—but clouds over late morning and afternoon. Scattered showers develop amid 30 mph wind gusts. High 61.

FRIDAY NIGHT: A few evening showers, then partly cloudy, windy and colder. Possible lake effect rain showers part of northwest Indiana. Low 41.

SATURDAY: Mixed sun, windy and chilly. Some lake effect rain showers possible downwind of Lake Michigan—and a slight chance of a sprinkle or brief shower in the afternoon elsewhere. High 54—the coolest daytime temp since early May.

SUNDAY and MONDAY: Partly cloudy, breezy and chilly. More clouds in the afternoons than the mornings—and a few lake effect rain showers possible in northwest Indiana.  High Sunday 54. Monday’s high 57.

TUESDAY AND WEDNESDAY: Sun and some mixed clouds. High Tuesday 59.  A little milder Wednesday. High 63.

THURSDAY: More clouds. Breezy. Growing chance for some showers. High 61.