Data
- Freeze dates and growing season: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991–2020, annual/seasonal product. We use the spring (PRBLST), fall (PRBFST) and growing season (PRBGSL) statistics at 36°F, 32°F, 28°F and 24°F, at 10%, 50% and 90% probability.
- Monthly temperatures and precipitation: NCEI monthly normals 1991–2020 for the same station.
- Hardiness zones: the ZIP code table published with the 2023 USDA Plant Hardiness Zone Map (USDA Agricultural Research Service and Oregon State University PRISM Climate Group).
- Places and ZIP codes: U.S. Census Bureau 2025 Gazetteer files (place and ZIP Code Tabulation Area locations) and 2025 population estimates.
- Frost forecast and alerts: National Weather Service forecast and active alerts for the location, refreshed about hourly.
Matching a place to a weather station
Of the roughly 15,600 stations in the normals dataset, 6,949 have complete 32°F spring and fall freeze statistics. Each city (using its Census internal point) and each ZIP code area (its centroid) is matched to the nearest of these stations by straight-line distance. We label the match:
- Close match: station within 25 km (about 16 miles).
- Reasonable match: 25–50 km.
- Distant station: more than 50 km; treat the dates as approximate.
Station matching uses distance only. Elevation, valleys, lakes and urban heat can make your location warmer or colder than the station, shifting frost dates by days or weeks.
Which cities have pages
Cities and towns with at least 5,000 residents (Census 2025 estimates) have frost date pages. Any ZIP code can be looked up with the search box. Each city’s growing zone is the zone of its nearest ZIP code area listed in the 2023 USDA table.
Updates
Climate normals are updated by NOAA once a decade; the next set (2001–2030) is expected in the 2030s. The frost forecast and alerts on each page update about hourly. Spotted an error? Tell us.