<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/white_halloween_2019.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/white_halloween_2019.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/white_halloween_2019.jpg?v=ap&w=980&h=551 800w" > Various shades of blue and white indicate the historical probability of a white Halloween. Weather stations must have at least a 40-year period of record and two or more white Halloweens to receive a color on the map. (Dr. Brian Brettschneider)

At a Glance The Rockies have the best odds of a white Halloween in the Lower 48.

Alaska and northern Canada have the highest probability in all of North America.

Most of the contiguous U.S. has less than a 2% chance of a white Halloween.

Halloween is only a week away, and the kids will soon be putting on their costumes for trick-or-treating. For some, they might need snow boots as a part of their wardrobe.

While forecast changes are likely in the days leading up to the holiday, Dr. Brian Brettschneider , climatologist at the University of Alaska-Fairbanks, compiled the map above, which shows the historical probability of a white Halloween across North America.

Brettschneider defined a white Halloween as a snow depth of 1 inch or greater on Oct. 31 or measurable snow (0.1 inches or greater) on that date.

In order to receive a color on the map, weather stations must have at least a 40-year period of record and have had two or more white Halloweens in the past, Brettschneider said in a tweet .

The majority of the Lower 48 has less than a 2% chance of experiencing a white Halloween, based on average weather conditions over many years.

The Rockies have the best chance of a white Halloween in the contiguous United States. Some other parts of the Mountain West and the Northern Plains also have noticeable odds of a white Halloween.

Breckenridge, Colorado, has a 43% probability of a white Halloween each year, while Denver's odds are lower – about 19%.

(MORE: Here's How Early in the Fall It Has Snowed In Your City)

Farther east, portions of the upper Midwest, northern Great Lakes, northern New England and New York's Adirondacks and Catskills have white Halloween odds of about 10% or slightly higher.

Marquette, Michigan, has a 12% chance of a white Halloween, while Old Forge, New York, has an 11% probability. A one-in-10 chance exists in Caribou, Maine.

The highest probability for a white Halloween in North America is located in Alaska and northern Canada, where there is greater than a 60% chance in some areas.

Most of the U.S.'s southern tier has never met the criteria for a white Halloween in recorded history, given the warmer temperatures typically present there than in the northern tier.

Brettschneider tweeted Wednesday that minus 7 degrees was the lowest temperature ever observed in the Lower 48 states at trick-or-treat time , which he defined as 7 p.m. local daylight time (6 p.m. local standard time). That occurred in 1984 in Havre, Montana, which also recorded the lowest trick-or-treat wind chill at minus 20 degrees .

However, those bitterly cold temperatures on Halloween are an anomaly. The map below from Brettschneider illustrates the typical temperature at trick-or-treat time, based on long-term averages.

A Rare Exception: 'Snowtober' Knocks Out Power to 3 Million in 2011

This rare, major October snowstorm dumped more than a foot of snow from northeastern Pennsylvania to southern Maine Oct. 29-30, 2011. Parts of Massachusetts and New Hampshire picked up more than 30 inches.

Some of that snow remained on the ground for Halloween.

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/snowtober2.jpeg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/snowtober2.jpeg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/snowtober2.jpeg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > Satellite image from Oct. 30, 2011, showing the area of snow produced by "Snowtober" from West Virginia to southern New England.

Trees were damaged and power lines were downed by the heavy, wet snow, causing more than 3 million to lose power. In some of the hardest-hit areas, power was out for more than a week. Playing a role in the tree damage caused by "Snowtober" was the fact that many trees still had leaves.

(MORE: Major, Damaging Snowstorms Can Strike in Early Fall)

A storm event review by NOAA said 39 direct and indirect deaths were blamed on the storm.

The name "Snowtober" was widely used to refer to the storm by those following it on social media and elsewhere.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.