Data and methodology

An almanac is only as good as its sources. Here is exactly where every number comes from, how each date is computed, and how the data stays current without a human babysitting it.

Climate data

All climate figures derive from the NOAA NCEI U.S. Climate Normals published by NOAA (NOAA). The Almanac currently computes from 2697 stations holding complete monthly temperature normals, 2618 of which also publish frost observations. Data last fetched 2026-06-12.

• Last spring frost and first fall frost are the mean date of the last spring and first fall frost over the 30-year normal period. They are averages. In roughly half of years, frost falls outside them.
• Frost-free period is the mean number of days between those dates.
• Winter tire windows are computed by the Almanac: monthly mean daily temperature normals anchored at mid-month with linear interpolation across the 45F (7C) threshold. That threshold follows tire-industry guidance on winter compound performance.

When you set a place, the Almanac uses your nearest station by straight-line distance. Microclimates are real: a valley floor or lakeshore can run a week or more off its station's record.

Rules and sources

Every external claim on this site links to the responsible source beside it, with the date we last verified it. Winter tires in the United States are a climate recommendation, not a legal requirement: there is no federal mandate, and the only road rules are the seasonal traction and chain controls some mountain states post on specific highways, which we point you to check at your state department of transportation.

The refresh pipeline

Reference sites die of staleness. The Almanac's data is refreshed by scheduled pipelines, not by memory:

• Climate normals re-fetch on a schedule and whenever NOAA publishes a new normals release.
• Rule pages are re-checked automatically; when a source page changes, a human is alerted the same day and the entry is re-verified before the change ships.
• Every dataset carries its last verified date in the open. If something looks stale, it says so.

What this site is not

General reference, carefully built, but not legal, financial, insurance, or safety advice. Laws change mid-year, leases and policies have their own terms, and frost ignores averages. For decisions with real consequences, confirm against the linked primary source.

Independence and revenue

The Home Almanac is independently built. Some pages may carry clearly marked affiliate links or quote forms. They never influence the dates, rules, or recommendations shown, and the site works identically if you ignore them. As an Amazon Associate, The Home Almanac earns from qualifying purchases. The full rules are published on the funding page.