When Freeze Season Starts and Ends, by Latitude
What the dates mean
NOAA's normals give, for each station, the date by which there is a 50% chance the first 32°F night of autumn has happened, and the date by which there is a 50% chance the last one of spring has passed. Half of all years, the first frost comes earlier than that date. County pages show these dates only where a county averages at least one such night a year; below that, a date is too noisy to mean anything.
First and last frost, by band
| Latitude | Counties | First 32°F | Last 32°F | Season |
|---|---|---|---|---|
| South of 33°N (Gulf Coast, south Texas, Florida) | 486 | November 19 | March 11 | 111 days |
| 33-37°N (Atlanta, Dallas, Memphis) | 731 | November 2 | April 2 | 151 days |
| 37-41°N (Kansas City, Denver, Philadelphia) | 934 | October 22 | April 19 | 179 days |
| 41-45°N (Chicago, Boston, Omaha) | 633 | October 8 | May 2 | 206 days |
| North of 45°N (Minneapolis, Montana, Alaska) | 304 | September 30 | May 12 | 225 days |
Medians across counties in each band. Elevation moves a county further than latitude does: the longest seasons in the data are Gilpin County, CO (292 days), Eagle County, CO (287 days), Bear Lake County, ID (287 days).
The date that matters for pipes
A first frost is a gardening date. The pipe date is the first night near 20°F, which in most of the country comes four to eight weeks later and is shown on each county page where it applies. Have outdoor spigots shut off and drained, hoses unhooked and attic or crawlspace runs sleeved before the first frost date. That leaves a margin for the year it comes early.
Where to go next
See the range: Hennepin County, MN, Cook County, IL, Harris County, TX, Miami-Dade County, FL.
How the County Freeze Numbers Are Made · How Cold Before Pipes Freeze? The 32, 20, 10 and 0 Rule