Nice Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Ukiah. A median date has an even chance of a later freeze in spring, or an earlier one in fall.
The last spring freeze typically comes around March 19 and the first fall freeze around November 20, a growing season of about 245 days.
- Median at 36°F
- last April 17, first November 2
- Median at 32°F
- last March 19, first November 20
- Median at 28°F
- last February 6, first December 5
Last freeze in spring
The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 9 | Apr 30 | Apr 24 | Apr 21 | Apr 17 | Apr 13 | Apr 9 | Apr 5 | Mar 31 |
| 32°F | Apr 15 | Apr 7 | Apr 2 | Mar 27 | Mar 19 | Mar 12 | Mar 4 | Feb 26 | Feb 13 |
| 28°F | Mar 13 | Mar 2 | Feb 23 | Feb 16 | Feb 6 | Jan 30 | Jan 19 | Jan 5 | Dec 25 |
| 24°F | Feb 24 | Jan 31 | Jan 24 | Jan 15 | Jan 7 | Jan 2 | Dec 28 | Dec 20 | Dec 11 |
| 20°F | – | – | – | – | – | – | – | – | – |
| 16°F | – | – | – | – | – | – | – | – | – |
First freeze in fall
The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 18 | Oct 24 | Oct 29 | Nov 1 | Nov 2 | Nov 5 | Nov 9 | Nov 13 | Nov 19 |
| 32°F | Nov 2 | Nov 7 | Nov 12 | Nov 15 | Nov 20 | Nov 24 | Nov 28 | Dec 3 | Dec 9 |
| 28°F | Nov 17 | Nov 23 | Nov 28 | Dec 1 | Dec 5 | Dec 9 | Dec 14 | Dec 24 | Jan 6 |
| 24°F | Nov 30 | Dec 4 | Dec 9 | Dec 13 | Dec 18 | Dec 26 | Jan 1 | Jan 8 | Jan 26 |
| 20°F | – | – | – | – | – | – | – | – | – |
| 16°F | – | – | – | – | – | – | – | – | – |
Growing season length
Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | 224 | 215 | 208 | 202 | 198 | 193 | 188 | 181 | 172 |
| 32°F | 285 | 272 | 261 | 251 | 245 | 237 | 231 | 223 | 212 |
| 28°F | 351 | 337 | 328 | 318 | 309 | 301 | 291 | 279 | 267 |
| 24°F | 365 | 365 | 365 | 365 | 365 | 353 | 343 | 336 | 321 |
| 20°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 |
| 16°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 |
How often it gets that cold
The share of years with at least one night at or below each temperature.
- 36°F or colder
- 100% of years
- 32°F or colder
- 100% of years
- 28°F or colder
- 94% of years
- 24°F or colder
- 51% of years
- 20°F or colder
- 9% of years
- 16°F or colder
- 0% of years
Degree days
A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.
- Heating degree days, base 65°F
- 3,030
- Cooling degree days, base 65°F
- 834
- Growing degree days, base 40°F
- 6,942
- Growing degree days, base 45°F
- 5,214
- Growing degree days, base 50°F
- 3,702
- Growing degree days, base 55°F
- 2,492
- Growing degree days, base 60°F
- 1,549
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 553 | 0 | 22 |
| February | 441 | 0 | 45 |
| March | 396 | 0 | 114 |
| April | 276 | 6 | 191 |
| May | 144 | 44 | 367 |
| June | 42 | 112 | 521 |
| July | 3 | 261 | 724 |
| August | 2 | 231 | 694 |
| September | 21 | 145 | 574 |
| October | 154 | 33 | 346 |
| November | 408 | 0 | 90 |
| December | 592 | 0 | 15 |
What this means
NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.
The station is 31.4 km from Nice. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.
More
Sources
NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00049122 (Ukiah). Public domain.