When signs of winter typically arrive where you live and how they’re changing

By CNN Meteorologist Chris Dolce, Matt Stiles, CNN

Hand in hand with brilliant foliage, fall delivers the first signs of winter to much of the United States — but the seasons are changing, and not as they normally do.

The fall season is heating up as the world warms due to fossil fuel pollution, and that’s pushing the date of the average first freeze — when the temperature hits 32 degrees or colder — later in the year for much of the country. That delay has impacts on everything from agriculture to allergens, and has also caused fall snow to decline.

The first freeze has shifted an average of 11 days later in 85% of 200 cities since 1970, according to the nonprofit research group Climate Central, with the biggest changes seen in the Midwest and Northeast.

When the first freeze arrives depends on a number of factors, including whether you live up a mountain, in the middle of a city, or close enough to an ocean or a big lake that takes the edge off the cold.

All these elements usually begin to align in September, bringing the first freeze to higher elevations of the Northern and Central Rockies, as well as locations from the Dakotas into the northern Great Lakes and higher elevations of Northern New England, according to 1991 to 2020 data averages from the National Oceanic and Atmospheric Administration. The freeze rollout expands toward the Midwest, Northeast and a larger part of the West in October, then into the South in November.

Here’s how that’s changing.

Freeze dates pushing later by weeks…

The biggest shift to later freeze dates has unfolded in the northern tier of the United States over the past few decades.

The first freeze has skewed at least two weeks later than in 1970 in nearly five dozen cities, mainly in the Upper Midwest and Northeast, but also parts of the Northwest, Climate Central found. That includes Detroit, Philadelphia and Minneapolis-St. Paul, just to name a few cities.

Reno, Nevada, has the biggest change, with its typical first freeze date now an eye-popping 41 days later.

The first freeze often kills or damages some vegetation, but not completely if it only stays that cold briefly. Later freeze dates can cause a longer fall allergy season and mosquitos overstaying their welcome, among other consequences. Warmer falls can also have a negative impact on non-citrus fruit and nut production by delaying the start of the critical winter chill period for flower and fruit production the following year.

…and that can also mean less snow

Seeing the first flakes of the season can be an exciting moment, while others might loathe the thought of early snows being a preview of winter’s shoveling to come.

Fall snow has decreased in every region of the US from 1970 to 2019, according to a Climate Central study.

Expanding that picture to include both winter and spring snow, nearly two-thirds of 2,041 cities Climate Central studied are seeing less snow than in the 1970s. Less snow can negatively affect water supplies by reducing meltwater from snowpack, especially in the Mountain West. It can also have an adverse impact on winter recreation and tourism. Winter has become the fastest-warming season for nearly 75% of the US as global temperatures rise.

When the first measurable snow arrives can be highly variable from year-to-year across both fall and winter.

The first accumulating snow of the season, defined as 0.1 inch or more covering the ground, historically hits the Northern and Central Rockies first in September, though higher reaches of these regions can see snow any time of year.

October’s first snows typically happen from a larger part of the Rockies into the Northern Plains, northern Great Lakes and far Northern New England.

November and December are when most of the Lower 48 sees its first accumulating snow, including the Midwest, Northeast and valleys of the Mountain West.

The country will still see snow even as fall and winter seasons warm, but climate change is affecting everything from snow timing to snow totals. A warmer atmosphere can hold more moisture, but if winter sees fewer freezing days, that could mean more rain than snow.

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