CHICAGO — The National Weather Service has issued a Winter Weather Advisory for Cook and Lake County from 6 p.m. to 11 p.m. Tuesday.

Also, the NWS has issued a Winter Weather Advisory for Porter and Lake County in Indiana from 8 p.m. on Tuesday to 5 a.m. on Wednesday.

Chicago’s Office of Emergency Management and Communications (OEMC) ask the public to drive safe as gusty winds, slippery conditions, and poor visibility can be expected Tuesday evening and night.

What a Halloween! This is one for the books. It’s not often Halloween here in Chicago has come with snow and this level of cold. 

It’s official—the day has produced measurable snow—defined at 0.1″ or more of snow on the ground—at the official O’Hare observation site. That makes today only the third Halloween in 138 years of official Chicago snowfall measurements in which the holiday has produced sticking storm—and only the 8^th Halloween with any snow at all in all that time dating back to 1884.

It appears the high temp for the day will come in at 38 or 39-deg. If true, only 4 Halloweens since 1871 (our temp records in Chicago go back further than our snow record—dating back to 1871) will have been colder with the two coldest Halloweens here having produced high temps of 32 in 1917 and 33 4 years ago when 3.4″ of snow fell in 2019.  

Adding to the upper 30-deg chill have been gusty northwest winds with gusts topping 30+ mph which have held wind chills in the 20s all day.  

At one point Tuesday afternoon, snow squalls here on Chicago’s far North Side produced a near white out rate of snowfall with a visibility I’d estimate at under 1/8^th mile. (See a snapshot of 3pm visibilities across the area in the visibility plot I’m attaching).

Model estimates keep snow showers going into the open hours of this evening—followed by clearing from Chicago west. Additional bursts of snowfall are likely and may lead to quick accumulations.  But the lake effect set-up is to linger more of the night in northwest Indiana and the potential is there for some additional accumulations, particularly away from the warmth of Lake Michigan. 

Much quieter weather takes over Wednesday through the end of the work week. Precip chances are nil during that period and temps will creep back to 50 Thursday and the mid 50s Thursday—coming close to 60 by Saturday.

Modeling hints at spotty weekend showers—but with a number of dry hours amid the more seasonable temps being predicted.

It’s early next week—i.e. Monday and Tuesday—when a wet autumn storm system is to bring more widespread and chilly rain to the area with some projections putting down over an inch of rain.  And in that system’s wake, chilly temps return with highs Tuesday forward next week likely to remain in the 40s (except close to 50 on Tuesday).

The sea change in temps which has occurred in the past week is quite dramatic.  Today’s 39-deg high will come in 44-deg colder than the 83 a week ago (last Tuesday).  And, while temps averaged 9-deg ABOVE NORMAL last week, they’re likely to average 6-deg BELOW NORMAL THIS WEEK. That means we’re experiencing a near 15-deg drop on the weekly average temp compared to last week.

Also of note: CLOCKS GO BACK AN HOUR before you turn in Sat evening. And November’s arrival a midnight tonight brings the fastest cooling month of the year—NOVEMBER—on line here. Normal temps drop from 55/40 Nov 1^st to 42/29 Nov 30th.  And hours of daylight are shrink another 62 minutes in the next 30 days.  Daylight today had already dropped off 4.82 hours (289 mins) from the longest day of the year back on June 21st.

HERE’S MY LATEST TUESDAY/HALLOWEEN EVENING CHICAGO METRO FORECAST (10/31/2023):

TONIGHT: Bursts of lake effect snow reducing visibility at times into tonight with local 1 to 3″ Illinois accumulations in harder hit locations—and as much as 2-4″ in harder hit areas of northwest Indiana.  Snow ends with clearing late tonight from Chicago west. Cold and breezy.  Low 27.

WEDNESDAY: Sunshine and mixed clouds, cold and moderately breezy. High 44—11-deg below normal.

WEDNESDAY NIGHT and THURSDAY: Partly cloudy.  Modestly milder by Thursday afternoon. Low Wed night 34. High Thursday 50.

FRIDAY: Extensive cloudiness and breezy with more seasonable temps. A shower or two possible in the afternoon but more likely at night. High Friday 56.

SATURDAY and SUNDAY: Partly cloudy to cloudy. Slight chance of a shower or two. High Saturday 59. Sunday’s high 58.

MONDAY and TUESDAY: Cloudy. A good chance of rain. Blustery northeast winds gust to 30 mph. High Monday 56. Chillier Tuesday. High 50.