Frost and freeze probabilities
NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), variables ANN-TMIN-PRBLST/PRBFST (36, 32, 28°F at 10–90% probability), ANN-TMIN-PRBGSL-T32FP50 and ANN-TMIN-PRBOCC-LSTH032. ncei.noaa.gov. Public domain (U.S. Government work). 7,125 stations used.
ZIP code locations
U.S. Census Bureau, 2026 Gazetteer Files, ZIP Code Tabulation Areas (33,791 ZCTAs, internal points). Public domain. ZCTAs approximate USPS ZIP codes; ZIP codes used only for P.O. boxes or single buildings may not be listed.
How we match ZIPs to stations
For each ZCTA we find the three closest stations with frost statistics by great-circle distance, and show distance and elevation so you can choose. We do not interpolate between stations.
Crop timing
Our own table, written from widely published U.S. Cooperative Extension planting-calendar guidance (weeks relative to frost dates, typical days to maturity and germination temperatures). Facts, not copied text.
What we don’t use
We do not show USDA Plant Hardiness Zones: the GIS data behind the 2012 and 2023 maps is owned by Oregon State University (PRISM Group), with conditions on logos and alterations, so it is not openly licensed. We do not scrape seed-company or other gardening websites.