A third consecutive mild, 100% sunny day in Chicago.  The last time we put three straight days of 100% of our possible sun together was Oct 1, 2 and 3—-a month and a half ago.

It’s Pacific air which is behind the beautiful weather—and Pacific air is DRY!! Dew points in the 20s underscore the fact—so do 20 to 25% relative humidities.  When you have dew points, which are a measure of atmospheric moisture, in the 20s and air temps in the 60s, THAT’S VERY DRY AIR!  

The Pacific air has much of the country running MILD. Nearly 87% of the Lower 48 has enjoyed 50-deg or warmer temps today—a percentage that will fall to half that level over the coming weekend as more seasonable cool autumn air moves in.

Dry air both warms by day and cools at night very quickly. So you get a WIDER THAN NORMAL SPREAD between daytime highs and nighttime lows.  From yesterday’s low 60-deg highs, nighttime lows crashed into the low 20s away from the warmth of the city and Lake Michigan.  Morning lows bottomed out at 21 in DeKalb County’s Shabbona; 22 at Elwood and Sugar Grove; 23 at Plainfield and Rockford and 24 at Oswego, Bonfield, Roselawn IN, Huntley, Rochelle, Coal City and Lake Barrington.  

The urban heat island effect and warming influence of Lake Michigan (with an average water temp at 52-deg right now) was on full display last night in the city. Heat retained and re-radiated by the buildings and asphalt acts to contribute some warmth to the air— as evidenced by lows of just 37 at Midway Tuesday morning.

The MILD DAYS HAVEN’T YET RUN THEIR COURSE! We have two beautiful days yet to go—with another day of nearly unlimited sun Wednesday and mixed sun through increasing clouds ahead of a cold front Thursday.  Highs reach 64 Wednesday and to within striking distance of 70 Thursday.  We still, however, have a chilly night ahead as the dry air allows rapid cooling back into the 20s away from the city and Lake Michigan.

Winds will pick up in coming days—especially as the pressure gradient tightens ahead of the incoming cold front on Thursday when gusts close to 40 mph are possible before the day is out.

There’s a period of showers, possibly even an isolated t-storms Thursday night as the cold front passes—but windy, much cooler weather hits Friday with high temps Friday likely to come in 16-deg cooler than Thursday.

Near seasonable weekend temps will feel cool compared to those we’ve been enjoying this work week with daytime 50s likely.

It’s next week some interesting developments take place—including a evidence a decidedly colder weather pattern is to fall into place.   Thanksgiving day—a week from this Thursday—looks likely to hold to the low 40s.

And all eyes are on a potential early week chilly rain system which could begin impacting Chicago late Monday and Tuesday.  The air could be chilly enough on that system’s back side to put some snowflakes relatively close-by.

Blocking patterns over Alaska and Greenland are expected to produce a “wavy” North American jet stream pattern later next week into the following week and the days immediately after.  That the kind of pattern in which steering winds reach from Canada south into the Lower 48 and deliver reinforcing lobes of cold air.  

Half of Novembers since 1901 here have produced at least some measurable snow in Chicago.  While we don’t have a specific system yet in sight, you tend to watch developments closely here this time of year if you’re a weather forecaster for any signs such a system might develop.


TONIGHT: Some patchy clouds late and chilly. Low 35 in the city—but low and mid 20s colder inland locations.

WEDNESDAY: Sunny, turning breezy and mild again by afternoon. High 64—a reading 15-deg above normal.

WEDNESDAY NIGHT: Scattered clouds, not quite as cold. Low 42—with mid 30s inland.

THURSDAY: Increasing cloudiness, becoming quite windy and unseasonably mild. Gusts above 35 mph by afternoon. High 68.

THURSDAY NIGHT and FRIDAY: A period of showers, possibly an isolated t-storm, developing late Thursday night with a few showers into early Friday, Then clearing, windy and much cooler Friday.  Low Thu night 36. High Friday 52—16-deg cooler than Thursday.

SATURDAY AND SUNDAY: Generous sunshine, breezy each day and seasonably cool. High Saturday 56. Sunday’s high 52.

MONDAY: Cloudy, strengthening east/southeast winds, similar temps. Growing prospects for rain later in the day—with a chilly rain likely and windy at night. High Monday 50.

TUESDAY: Windy and chilly with cold rain. Some wet snow may occur as the day proceeds here or nearby. High 46.