At a Glance
October weather changes in the U.S. typically result from increasing contrasts in temperatures because of diminishing daylight and a southward migration of the jet stream from its late-summer vacation in or near Canada.
But not all of these changes are related to colder air.
Some aspects of October weather worsen wildfires. Another typical shift makes one U.S. state's hurricane threat higher in October than any other month.
Here are six typical changes we see during the first full month of fall.
In October, the season's first 32-degree low temperatures begin to migrate from the high country of northern New England, the Rockies and areas near the Canadian border into much of the interior Northeast, Great Lakes, Midwest, northern and central Plains, and High Plains of the Rockies.
This includes areas as far south as the Smoky Mountains of Tennessee and North Carolina, parts of the Oklahoma and Texas Panhandles, and northern New Mexico.
Typical date of the first freeze of the season, based on National Weather Service 30-year average data.
Given all those crisp, cool nights, October is when the large majority of the Northeast, Midwest and West sees the best, most vivid fall colors.
Typical time of peak fall colors. Much of the Northeast, Midwest and West see peak colors in October.
With this increasingly cold air, accumulating snow previously restricted to the highest peaks of the Rockies and Alaska in September begins to blanket lower elevations of the High Plains, parts of the northern Plains and northern Great Lakes, Appalachians, Adirondacks, Green and White Mountains in October.
Some cities that typically see their first measurable snow in October are Caribou, Maine; Marquette, Michigan; Duluth, Minnesota; Bismarck, North Dakota; Great Falls, Montana; Denver; and Anchorage, Alaska.
Month of the average first accumulating (0.1 inch or greater) snowfall of the season, according to 30-year average statistics.
Superstorm Sandy in 2012 was the ultimate recent example of a massive October storm. One of Sandy's unique impacts was its feet of snow burying parts of the Appalachians.
But there have been a number of other recent big October storms:
Local residents watch as crews clear fallen trees Oct. 16, 2006, in Amherst, N.Y., a suburb of Buffalo, N.Y.
September may be the peak month for hurricanes in the entire Atlantic Basin, but in Florida, October is a month feared just as much.
From 1851 through 2016, 32 hurricanes made a Florida landfall in October, dwarfing the state with the second-highest number of October landfalls: Louisiana, with nine.
In South Florida, October is the month with the most hurricane direct hits. According to NOAA's Best Track Database, 23 October hurricanes have passed within 100 nautical miles of downtown Miami since 1851.
Over the past two Octobers, we've seen Hurricane Matthew rake up the coast from Florida to the Carolinas, preceded the previous October by Hurricane Joaquin raking the Bahamas as historic flooding swamped South Carolina.
These are the typical areas for development and tracks of Atlantic Basin tropical cyclones in October.
Southern Calfornia's infamous offshore winds, known as Santa Ana winds, typically kick into gear by October, according to a 2017 climatology study.
Fueled by a combination of high pressure in the Great Basin and the southward return of the jet stream, these hot, intense winds squeeze through passes and canyons of the L.A. Basin, at times, from fall through spring.
What makes them particularly dangerous in October is that they occur when soil moisture is at its driest after the summer dry season. These Santa Ana winds can whip either an existing wildfire or just-developed small brush fire into an inferno.