Freeze dates at 10%, 50% and 90% odds from NOAA’s 1991-2020 normals, with planting dates
Updated October 2026
NOAA’s National Centers for Environmental Information compute freeze dates by simulating each station’s 1991-2020 record thousands of times. For spring, each date gives the chance that the last 32°F night comes on or after it; for fall, the chance that the first one comes on or before it (NCEI Normals Calculation Methodology, 2020).
| Probability | Spring (last 32°F) | Fall (first 32°F) |
|---|---|---|
| 10% | Late date: a 1-in-10 chance of frost after it | Early date: a 1-in-10 chance of frost before it |
| 50% | The usual “average last frost”: even odds | The usual “average first frost”: even odds |
| 90% | Early date: a 9-in-10 chance of frost after it | Late date: a 9-in-10 chance of frost before it |
At Columbus’s Port Columbus airport station (USW00014821) the spring dates are May 5, April 18 and April 4, and the fall dates October 14, October 27 and November 7. Planting tender crops on the 50% date means a frost after planting in about one year out of two.
| Place | Station | Spring 10% | Spring 50% | Fall 50% | Fall 90% |
|---|---|---|---|---|---|
| Columbus, OH (Port Columbus airport) | Columbus Port Columbus Intl Ap, OH | May 5 | Apr 18 | Oct 27 | Nov 7 |
| Denver, CO (ZIP 80202) | Denver Water Dept, CO | May 13 | Apr 30 | Oct 12 | Oct 26 |
| Atlanta, GA (ZIP 30303) | Atlanta Fulton Co Ap, GA | Apr 10 | Mar 24 | Nov 8 | Nov 26 |
| Helena, MT (regional airport) | Helena Rgnl Ap, MT | May 25 | May 9 | Sep 30 | Oct 11 |
| Dallas, TX (Love Field) | Dallas Love Fld, TX | Mar 19 | Mar 2 | Nov 29 | Dec 18 |
| Miami, FL (ZIP 33101 area) | Miami Intl Ap, FL | Freeze too rare to compute | |||
Dates for warm stations can fall in the previous or next calendar year: NOAA counts the freeze season from August 1 to July 31, so Phoenix’s “last” frost at 50% is in early January. Stations where 32°F occurs in too few years, such as Miami’s airport, have no dates at all.
The University of New Hampshire Cooperative Extension’s planting chart counts from the average last frost: broccoli goes out 2 to 4 weeks before it and lettuce 3 to 4 weeks before, tomatoes and cucumbers 1 to 2 weeks after, peppers and squash 2 weeks after, and beans are sown after it. The same chart gives indoor seed-starting times of 6 to 8 weeks for tomatoes, 8 to 10 for peppers, 4 to 6 for broccoli, 4 to 5 for lettuce and 3 to 4 for squash and cucumbers; leave the weeks field at 0 to use them. Use the 10% spring date instead of the 50% date for frost-tender plants if you would rather not cover them on a late cold night.
It shows long-term probabilities, not a forecast; watch your local forecast in spring and fall. It uses 32°F only (NOAA also publishes 28°F and other thresholds), ZIP areas by their three-digit prefix, and stations with standard, representative or provisional normals. Alaska and Hawaii ZIP prefixes cover huge areas, so search by station name there. For crop timing in your county, your state’s cooperative extension office is the best local source.