I'm dreaming of a white… Halloween?
In order to qualify for a white Halloween, there must either be at least 1 inch of snow on the ground on the morning of Oct. 31 or falling snow must accumulate to at least 0.1 inches on that date. This is the same criteria the National Weather Service uses to define a white Christmas.
The historical probability of a white Halloween. (Dr. Brian Brettschneider)
The map is based on historical weather data averaged over many years. Brettschneider noted that snowfall observations had to date back at least 40 years for a location to be included in his analysis.
In the Lower 48, trick-or-treaters have the highest odds of encountering snow on Halloween in the higher elevations of the northern and central Rockies, ranging from a 25% to 50% chance in the highest peaks west of Denver and in parts of Yellowstone National Park in northwestern Wyoming.
The probability is lower, 10% to 25%, for most of the Rockies, however. Parts of the Washington and Oregon Cascades, northern Plains, northern Minnesota and the western Upper Peninsula of Michigan also have 10% to 25% odds of a white Halloween.
An autumn pumpkin with some snow in its eyes on Tuesday, Nov. 20, 2018. (Brianna Soukup / Portland Press Herald / Getty Images)
A snowy Halloween is uncommon for the rest of the Lower 48, where the probability is generally less than 10%.