Fall arrives in Chicago tonight. This is when you can expect the first frost and snowfall.

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Raise a Pumpkin Spice Latte to celebrate the return of fall — the fall equinox takes place tonight at 8:03 p.m.

That’s when the sun shines evenly in both the northern and southern hemispheres — making day and night nearly equal — before crossing the equator to head south. We will lose a little more sunlight each day until the winter solstice on December 21, the shortest day and longest night of the year. The same phenomenon will happen again next year on the occasion of the vernal or vernal equinox on March 20, 2023.

However, meteorologists said goodbye to summer on September 1, preferring to track the weather in four- to three-month increments rather than astronomical seasons, which are determined by equinoxes and solstices.

It’s the perfect time to observe Chicagohenge.

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The rising and setting sun aligns perfectly with the city’s east-west street pattern, creating spectacular photo opportunities as the sun is framed by the Chicago skyline.

The earliest first freeze occurred on September 22, 1995 at O’Hare International Airport, the city’s official shooting site. The last was November 24, 1931.

In 2021, the first freeze did not come until November 2.

“The first freeze, which is when the temperature drops to 32 degrees or less, usually occurs between October 11 and 12 in the suburbs of Chicago and between October 21 and 30 in the city and along the lakeshore,” Brett Borchardt , a meteorologist for the National Weather Service’s Chicago office told the Tribune.

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Chicago experiences higher temperatures longer than the suburbs due to the heat island effect. Its location next to the warm waters of Lake Michigan explains why the city and nearby suburbs freeze later in the year than their more distant counterparts.

Frost can develop on clear nights when air temperatures are in the mid-30s, but can be scattered. That’s why, says WGN-TV chief meteorologist Tom Skilling, the weather service “doesn’t track frost statistics, but instead uses the first-season temperature of 32 (degrees) or below to determine the end of the growing season.”

“The first track or more of snow usually occurs on October 30, but is already on September 25 (1942) and not until December 5 (1999),” Borchardt said. “The first measurable snow (0.1 inches or more) usually occurs around Nov. 17.”

[ Here’s when Chicago received its first snow of the fall season, going back 135 years ]

Last year, Chicago received its first measurable snowfall of the season on December 28 — the last date of a first snowfall in Chicago history dating back to 1885.

La Niña lingers. According to the World Meteorological Organization, the climate pattern that has a cooling effect on ocean surface temperature is expected to last until the end of the year. This is the third consecutive year – or a rare “triple dip” – of the weather phenomenon.

“It’s unusual for a La Niña to last through the summer, and even more unusual to go into a third consecutive La Niña — which is what we would do if it lingered into the fall,” said Illinois state climatologist Trent Ford. .

Locally, the National Weather Service’s Climate Prediction Center predicts temperatures above normal and “equal opportunities” for above or below precipitation from October to December.

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