First Frost Date by 10%, 50% and 90% Chance
The first-frost date is a probability, not a promise that the temperature will freeze on that day. NOAA's climate normals list dates for the first fall night at or below 32 °F at each station. The percentage tells how often that threshold has already happened by the listed date.
Three probability dates for fall
- 10%: the early date. There is about a 10% chance a 32 °F night has happened by then; use it when planning conservatively around a tender crop.
- 50%: the middle date. In half of the years represented by the normals, the first freeze has arrived by about this point.
- 90%: the late date. By then a first freeze has happened in about 9 years out of 10.
For a 32 °F first freeze, the dates in these three NOAA stations are:
| NOAA station | 10% (early) | 50% (middle) | 90% (late) |
|---|---|---|---|
| Columbus Port Columbus International Airport, Ohio | Oct 14 | Oct 27 | Nov 7 |
| Cleveland, Ohio | Oct 21 | Nov 3 | Nov 17 |
| Austin Bergstrom Airport, Texas | Nov 1 | Nov 16 | Dec 5 |
These are station normals for 1991–2020. They describe the distribution of past dates at each station; they do not forecast a particular fall. Your garden can differ because of distance, elevation, slope, buildings and other local conditions.
Which date should guide the garden?
Start with the crop's tolerance and the consequence of a freeze. The 10% date gives more time to harvest or protect a frost-sensitive plant. The 50% date is a useful middle estimate for planning. The 90% date helps describe how late a first freeze can be in many years, but waiting for it leaves less buffer for a tender crop.
Use the station nearest your garden as a starting point, then watch the local forecast as fall approaches. Frost can occur in a sheltered or low-lying garden differently from the nearby station. For protection thresholds and cover choices, see how to protect plants from frost; for crop groups, see frost-tolerant vegetables.
The station finder shows first-fall and last-spring dates at 32 °F, plus the 36 °F frost and 28 °F hard-freeze thresholds. Choose the state and station closest to you.
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal station data.
- NC State Extension, Interpreting Freeze/Frost Probabilities, for the meaning of 10%, 50% and 90% dates.