Tool · NOAA 1991–2020 freeze probabilities
Frost Risk by Date
The chance of a frost after a planting date, or before a harvest date, for any US ZIP code.
Frost risk on May 1 in Burnsville, MN
In Burnsville, MN, the chance of at least one more night at or below 32°F after May 1 is 25%, from NOAA's 1991–2020 freeze statistics at Minneapolis/St Paul Airport, MN. Waiting 6 days, to May 7, brings the risk down to one year in ten. Across the whole of May, at least one 32°F night came in 25% of years.
| Night as cold as | Chance of one after May 1 | Winters reaching it |
|---|---|---|
| 36°F | 60% | 100% |
| 32°F | 25% | 100% |
| 28°F | under 10% | 100% |
| 24°F | under 10% | 100% |
Frost dates and weather by month for 55337 (Burnsville) →Compare with another ZIP →
How the chance is worked out
NOAA publishes, for every station with a long enough record, nine dates for each temperature: the dates after which a night that cold came in 90%, 80% and so on down to 10% of the springs of 1991–2020, and the same for the first night of fall. For a date in between, the tool reads the chance off the two nearest of those dates, assuming it changes evenly between them. A date in January to July is read as a planting date (the chance of another frost after it); August to December as a harvest date (the chance the first frost has already come).
In the example, Minneapolis/St Paul Airport, MN — the station for ZIP 55337 — saw its last 32°F night of spring after April 8 in nine years out of ten, after April 23 in half of them and after May 7 in one year in ten. That is why the chance on May 1 sits between 10% and 50%.
Where a temperature is not reached every winter, NOAA's dates describe only the winters that reach it, so the tool multiplies by the share of winters that do. Frost also forms on clear, still nights in low spots at 33–36°F, which is why the 36°F row is there. These are thirty-year statistics for the station, not a forecast.
Every ZIP code page has the full table of dates; to set two places side by side, use compare two places. Sources and limits: methodology.