Why Your Own Yard Might Not Match Your ZIP Code's Number

Distance to the reporting station

Every figure on this site comes from the nearest NOAA station that reports it, which in a rural area can be a real distance away. The further a ZIP is from its matched station, the more room there is for a genuinely different local climate, especially in mountainous or coastal terrain where conditions change quickly over short distances.

Elevation and slope

Cold air sinks. A low-lying yard or the bottom of a slope collects cold air on a still night and frosts earlier and harder than a station sited on flatter or higher ground nearby, sometimes by weeks. A south-facing slope, by contrast, can run measurably warmer than the valley floor below it.

Urban heat and water

Pavement, buildings, and dense development hold heat overnight and can push a city center's real last frost earlier than a station sited at an airport on the edge of town. Large bodies of water have the opposite, moderating effect on whatever is immediately downwind of them.

What to do with that

Treat this site's date as the regional normal, not a guarantee for one specific yard, and weight it toward the riskier end of the range described in the range guide if your own garden sits in a low spot, far from the matched station, or in an unusually exposed or sheltered microclimate you already know about from past seasons.

Where to go next

See the range this plays out across: Stanley, ID, Farber, MO, Indian Creek, FL.

How FrostDateCheck Calculates Your ZIP Code's Frost Dates · Hardiness Zone vs. Frost Date: Different Questions