About this map
Each county is colored by its typical first freeze: the date by which, in half the years from 1991 to 2020, the low had already reached 32°F or colder for the first time that fall. The dates are NOAA’s U.S. Climate Normals for 168 North Carolina weather stations1,2. A county with more than one station takes the middle of their dates. Nine counties have none of these stations, so each takes the station nearest its center, and its tooltip says which. The mainlands of Dare and Hyde, where every station I used is on an island, take the nearest mainland station. I left out 19 stations whose normals NOAA marks as estimated, most of them with fewer than 10 years of records2.
Typical means half the years. At Raleigh-Durham International Airport, NOAA puts the chance of a first freeze by Oct 23 at 1 in 10, by Nov 4 at 1 in 2, and by Nov 17 at 9 in 101. Within one county the dates can be weeks apart: in Haywood County, the Cataloochee station, at 2,650 feet, typically sees its first freeze by Oct 12, and Waterville, at 1,430 feet, by Nov 1.
The islands freeze last. Cape Hatteras’s typical first freeze is Dec 22, Ocracoke’s Dec 20 and Manteo’s, on Roanoke Island, Dec 6, while on the mainland across the sound, the Gum Neck station in Tyrrell County typically sees its first by Nov 131. Where the Census map draws a barrier island, or Roanoke Island, as its own piece3, I colored it by the station on it, or else the nearest island station. Harkers Island, in the sound, and the islands the map joins to the mainland, like the Currituck Banks, take their county’s color.
Press Play to watch the freeze cross the state, the mountains first (Ashe County’s typical date is Oct 9) and the Outer Banks last. By Nov 7, 68 of the 100 counties have typically had their first freeze.