We’re just over a day away from closing the books on Sept and moving into the month of October, 2023.
We’re to make the transition in phenomenal meteorological fashion with a sun-filled, rain-free, unseasonably warm autumn weekend on the way.
Chicago is to benefit from an abnormally warm late season pattern locked in place into mid next week by an atmospheric blocking pattern. NO RECORDS will occur here—though predicted high temps will top out just under 10-degrees from the low 90-deg records currently on the books.
RECORDS ARE IN JEOPARDY in multiple states to Chicago’s west. Remarkable late season 90s in the Plains and western Midwest are likely to break some daytime high temp records in portions of 11 states there.
Daytime temps in Chicago are to surge into the 80s Saturday through Wednesday—June and July level temps.
Each of the coming 5 days (through Wednesday) is to post 10 to 14-deg temp surpluses.
Lake breezes will blow from the southeast each day into early next week limiting beach temps to the mid 70s but with shoreline Lake Michigan water temps ranging around the south end of the lake ranging from 58-deg to as warm at 68-deg on Chicago’s lakeshore. SO WE HAVE WHAT AMOUNTS TO LATE SEASON BEACH WEATHER
And mariners heading out onto Lake Michigan do so in a relaxed pressure gradient within a ridge of high pressure which assures gentle winds likely to stir little more than mere “ripples” on Lake Michigan.
We close the books at midnight Saturday night on a September which ranks among the 17% warmest of the 153 on record since 1871—having averaged close to 2.5-deg above normal. And Sept, with its 3.36″ currently on the books AND NOT ADDITIONAL RAIN EXPECTED between now and the month’s close is to come in among the city’s 36% warmest of the past 153 years,
A BIG PATTERN CHANGE HITS the back half of next week as the blocking pattern breaks down and jet stream level steering winds shift into the area from Canada. This is to bring Chicago a real taste of autumn air and quite possibly the city’s coolest temps in 5 months (since last May). While this weekend sees highs in the 80s and lows in the low 60s in the city, next weekend is to see highs only in the 60s with nighttime lows in the mid 40s.
If current forecast trends hold, NEXT WEEKEND IS LIKELY TO AVERAGE 18-DEGREES COOLER THAN THIS WEEKEND. THAT’S A BIG CHANGE!
This isn’t unexpected. Chicago’s observational records shows normal October temps drop from 69/51 on the first to 56/40 by months end. OCTOBER IS TYPICALLY CHICAGO’S 2nd FASTEST COOLING MONTH OF THE YEAR seeing average temps pull back an average of 12-deg. NOVEMBER is the fasted cooling month of the year losing an average of 13-deg.
HERE’S MY LATEST FRIDAY CHICAGO METRO FORECAST (9/29/2023)
TONIGHT: Mainly clear and hazy with some fog re-developing, especially in cooler areas away from the city and Lake Michigan. Low 59—but low to mid 50s cooler inland locations.
SATURDAY THROUGH MONDAY: Daytime temps warm to summer levels. Mostly sunny days and mainly clear nights. Fog patches possible late nights and morning in cooler inland locations. High Saturday 82 with 83-deg highs Sunday and Monday, Light southeasterly daytime lake winds will produced mid 70-deg high on Chicago area beaches. Nighttime lows 61—with some mid 50s cooler inland locations.
TUESDAY: Generous sunshine, unseasonable afternoon warmth continues. Better organized south/southwest winds may greatly limit any lakeside cooling. High 84.
WEDNESDAY: Partly sunny, becoming breezy from the south/southwest and warmer. High 84.
THURSDAY: More clouds and showery with some possible t-storms. Not as warm. High 76.
FRIDAY: Windy and a good deal cooler. Mixed morning sun—but clouds build and a few scattered light showers possible in the afternoon. Gusty northwest winds. High 69.
