September 2023 opens on a beautiful note: 100% sunny and comfortable with a slightly-above seasonable high which is likely to end up at 85-deg (the “normal” high this time of year is 80).

WE’RE HEADED IN A LABOR DAY WEEKEND WHICH IS TO BE UNSEASONABLY HOT—and which is to see the DRY SPELL that has seen us move into a 15th day without so much as a drop of rain here in Chicago—CONTINUE!  

This weekend is to average 11-DEG WARMER THAN LAST WEEKEND with its highs of 77 and 75-deg on Saturday and Sunday respectively. That’s quite an increase!

And, this warm-up is to come with a well organized “off-shore” SW wind flow likely to push the heat right up to and out over Lake Michigan—making this a phenomenal BEACH WEEKEND for those heading to area beaches.  And that’s true for Saturday, Sunday and Monday. Chicago’s shoreline water temps are near summer season highs running in the low 70s.

The weekend heat is the result of a HUGE DOME OF HOT AIR developing over the nation’s mid-section—a region of the atmosphere in which air sinks, warming and drying in the process.

If current forecast trends verify, we’re may well be headed for 5-consecutive days of 90-deg or greater high temps. The record for most consecutive 90-deg high temps in the early weeks of September in 6 days set in Sept 1978, 1959 and 1831. We may fall just shy of making that record—BUT FIVE 90s IN A ROW WOULD BE IMPRESSIVE.

Temps each of the coming 5 days—Saturday through next Wednesday appear likely to each average 7 to 14-deg above normal.  

The warming air mass will produce its 90-deg highs Saturday and Sunday in an environment with dew point, a measure of atmospheric moisture, quite subdued—only reaching the mid 50s.   BUT THE HUMIDITY BEGINS TO ARRIVE Monday, Tuesday and Wednesday— a development which is likely to convert the hot spell into one which is uncomfortably humid with PEAK HEAT INDICES rising from Saturday’s 91 and Sunday’s 98—to a 104 degree readings Monday and near 100-deg Tuesday and Wednesday, the product of dew points rising to 70 marrying to predicted low and mid 90-deg high temps.

A high of 97 Monday (Labor Day) would put the area in RECORD HIGH TEMP TERRITORY.

With the influx of more humid tropical air Monday and Tuesday, we’ll see the sky fill with cottony summertime-type cumulus clouds. And while chances are not HIGH—an isolated t-storm can’t be completely ruled out.  But it’s Wednesday and/or Wed night which may see the best chance of some t-storms—though prospects for storms fall in the 30-40% range at the moment.

THOUGH THE INTENSITY OF THE HEAT IS TO EASE later next week, temps going into the following week are to continue above normal.  Current model trends produce a weekly average this week a bit over a degree below normal—but WARM NEXT WEEK’S AVERAGE TO TO 9-degrees above normal and the following week to over 5-deg above normal.  SO the opening half of SEPTEMBER 2023 appears likely to be A WARM ONE.

Full forecast details and more at the WGN Weather Center blog

TONIGHT: Mainly clear, not quite as cool as recent nights.  Low 64—but upper 50s coolest inland locations.

SATURDAY:  Generous sunshine, turning breezy and hot—but with humidities remaining restrained.  High 92—with NO LAKESIDE OR BEACH COOLING. Southwest winds gusts pick up to near 25 mph at times. 

SATURDAY NIGHT: Scattered clouds diminish, warmer. Humidities remain comfortable. Low 69.

SUNDAY: Mostly sunny, windy and hot. Only moderate humidities. High a near record or record 99—with similar peak afternoon heat indices.  

MONDAY (Labor Day):  Sunshine mixed with developing summerlike cottony cumulus clouds. Breezy, hot and with humidities higher.  High a near record or record 97 with a peak afternoon heat index of 100 to 105.

TUESDAY: Partly sunny, breezy, hot and humid. Slight chance of an isolated afternoon. High 93—peak heat indices approaching 100-deg.

WEDNESDAY: Parly cloudy, hot and humid. Scattered t-storms possible.  High 92—peak heat index 97.

THURSDAY: A good deal of sunshine—just scattered clouds, not as hot or humid. High 83.

FRIDAY: Mostly sunny, comfortable. High 83—but lower lakeshore.