ANOTHER 80+ DEG DAY in the fantastic run of late season warmth.  Temps hit 84 at O’Hare—16-deg above normal!!  Not bad, huh??

This makes 5 consecutive 80+-deg days in a row! It marks the 15^th consecutive day of ABOVE NORMAL TEMPS. Remarkably—each of the past 5 days have posted double-digit temp surpluses—NOT the easiest thing for nature to pull off at a time of the year with 4 hours less daylight and the sun 30-deg lower in the daytime sky, thus producing sunlight delivering reduced energy,.

But AUTUMNAL NIRVANA is about to end as a buckling jet stream sweeps air out of Canada into the Chicago area.

Multiple cold frontal passages are to take temps BELOW NORMAL by Friday with this weekend to see the coolest temps which have visited Chicago in 5 months (since early May).  We expected daytime highs from Friday through Sunday to only make the 50s and nighttime lows to dip into the low and mid 40s.

Our analysis has daytime averages BELOW NORMAL Friday (-7 deg), Saturday (-10 deg), Sunday (-7 deg), Monday (-6 deg) and Tuesday (-3 deg),

Gusty northwest winds lock in in coming days—especially Friday, Saturday and Sunday when the chill is to ride 30 mph daytime wind gusts into Chicago.

The coming weekend is to produce temps more than 20-deg cooler than last weekend—a big drop!

The transition features some low coverage scattered showers impacting perhaps 20% of the area this evening —the “lift” generated by an upper disturbance is to increase shower coverage as the night proceeds. By morning—and in hours just past daybreak Thursday, as much as 70% of the metro area is in for rain—and thunder chances, while not  high—aren’t zero either. 

Showery weather may linger into the afternoon—particularly southern suburbs and northwest Indiana.  But clouds are likely to break with the cooler air circulating in during the afternoon and evening hours.

Cold air aloft Friday means Friday’s sunny open is to give way to clouds and instability showers and like to fall from those clouds in the afternoon. We’re likely to repeat that cycle in the blustery, chilly air which is to be in place Saturday, Sunday and even Monday.  Showery spells will be scattered  and occupy only a portion of each day, but some rain—albeit scattered—can’t be ruled out in the “warmer” hours of each of those days.

WARMING—though nothing close to the warmth we’ve enjoyed the past several days—stages a comeback mid-week next week.  Temps could be approaching 70 Wed and Thu.  But another surge of cool, unstable air drops temps, increases clouds and produces some chance of rain later next week into the following weekend.

A NOTE OF INTEREST—Snow flurries occurred on this date 9 years ago—Oct 4, 2014. 

HERE’S MY LATEST CHICAGO METRO FORECAST (10/4/2023)

TONIGHT: Cloudy and mild. Spotty sprinkles or brief showers early give way to growing shower coverage as the night proceeds. Rain will have occurred over 70% of the area by morning and isolated thunder isn’t out of the question.  Low 66.

THURSDAY: Rainy spells are likely through the morning commute period over parts of the area—especially from Chicago south.  Rain may linger into afternoon south suburbs and northwest Indiana.  But partial clearing is expected later in the day from the northwest. Breezy and noticeably cooler. High 74.

THURSDAY NIGHT: Clearing, breezy and cooler.  Low 54—but upper 40s inland.

FRIDAY: Opens with sunshine –but clouding over, windy and much cooler. Showers develop in the afternoon and continue into Friday night.  High 56.

SATURDAY, SUNDAY AND MONDAY: Cloudy spells after some mixed morning sun, fairly windy and chilly. A few spotty showers are possible—most numerous downwind of Lake Michigan in northwest Indiana.  High Saturday 54; Sunday’s high 58. High Monday 60.

TUESDAY: Partly sunny, modestly warmer. High 63.

WEDNESDAY: Mostly sunny and warmer. High 68.