When is my last frost, and my first freeze?
In the US, type your ZIP code to see the odds for both; anywhere else, your city’s name. You get the date half of years have frosted by, the date it still frosts 1 year in 10, and the same pair for the freeze that ends the season. In the US they come from the nearest NOAA weather station, named, so you can weigh them yourself. A city abroad reads a weather model, and its answer says so.
Why a frost date is not a date
A last-frost date is really a percentile, drawn from 30 years of records at a nearby weather station. In about half of years a frost still comes after the median date. The tool above shows the median beside the 1-year-in-10 date, so you can choose how much risk to take.
Spring frost and fall freeze, side by side
Gardeners ask about both ends of the season. The last spring frost decides when it’s safe to set out a tomato. The first fall freeze decides whether what you sow in August has time to finish. Each is a range of dates, and in each the 1-in-10 date is the one to watch. In spring that’s a frost that comes late; in fall, a freeze that comes early. Enter a US ZIP code and you get both, from the same station with the same percentiles. Whichever is closer to today shows first.
Where these numbers come from
NOAA NCEI 1991–2020 U.S. Climate Normals from 4,350 weather stations. 33,047 of the 33,144 U.S. ZIP codes have a station within 80 km. Each ZIP code reads the station the Milpa planner uses for it, the nearest one, and every date is that station’s own recorded percentile, unshifted. Near a few cities the planner uses a hand-built site instead, where a station’s dates were corrected for terrain with PRISM temperature maps, and the answer says so. Nothing else in a US answer is modeled or averaged. It is the same committed table behind every location page on this site, read a second way. A city abroad, typed by name, has no NOAA station to read, so its answer comes from a weather model’s daily lows instead, graded and credited as its own frost page credits them.
What this tool will not do
It won’t call a weather service, guess a number for a ZIP with no station near it, or tell you your hardiness zone. The zone answers a different question, which perennials survive your winter, and it can’t tell you when to sow. This tool gives frost odds from records, or says it can’t.