About and Methodology

This site lists frost dates for U.S. weather stations. Each station page is built from the station’s own records; there are no pages without data.

Where the data comes from

• Frost dates and the frost-free season come from the NOAA National Centers for Environmental Information (NCEI) U.S. Climate Normals for 1991–2020, one file per weather station. Each station page links to its source file.
• Hardiness zones are derived from the PRISM Group 2023 hardiness zone grid (Oregon State University) at the station location.

How to read the dates

The dates are probabilities computed from about 30 years of weather, not a forecast for a particular year.

• Spring (last frost): a date with a 10% probability means that in about one year in ten a frost still happens after that date. At 50% half of the years are earlier and half are later. At 90% a frost after that date happens in most years.
• Fall (first frost): a date with a 10% probability means that in about one year in ten the first frost arrives before that date.
• 32°F is a light frost that damages tender plants; 28°F is a hard frost.

Why the zone is “derived”

The hardiness zone on each page is our classification of the PRISM 2023 grid value at the station’s coordinates: zone derived from PRISM 2023 grid at the station location (not the official USDA map). It can differ from the zone the official USDA Plant Hardiness Zone Map shows for a nearby ZIP code.

Which stations are included

• Only stations whose NOAA normals carry the completeness flag S (standard: at least 24 years of data meeting WMO standards).
• Only stations with at least 25 years of frost records.
• Only stations where a 32°F frost happens every year. Warmer stations, where frost does not occur every year, are excluded, so the warmest southern zones (10 and above) are not covered.
• Only stations inside the PRISM grid for the contiguous United States (no Alaska, Hawaii or Puerto Rico).

Explanatory text

The explanatory paragraphs on station pages are written with the help of a language model and checked automatically before publication: every date and number in the text must match the station data. The tables are generated directly from the data.

Updates

Data last updated: 2026-10-08.

Site operator: Individual Entrepreneur Anton Kozyrev (country of Georgia), ID 304822565, trading as AnKo Software Labs. Contact: contact@ankosoftlab.com.