Fulton Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Santa Rosa. 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 February 25 and the first fall freeze around December 1, a growing season of about 279 days.
- Median at 36°F
- last April 3, first November 14
- Median at 32°F
- last February 25, first December 1
- Median at 28°F
- last January 20, first December 16
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 | Apr 25 | Apr 18 | Apr 12 | Apr 8 | Apr 3 | Mar 30 | Mar 23 | Mar 15 | Mar 6 |
| 32°F | Mar 29 | Mar 16 | Mar 7 | Mar 1 | Feb 25 | Feb 18 | Feb 11 | Feb 1 | Jan 21 |
| 28°F | Feb 24 | Feb 11 | Feb 2 | Jan 27 | Jan 20 | Jan 13 | Jan 6 | Dec 30 | Dec 22 |
| 24°F | Jan 31 | Jan 19 | Jan 12 | Jan 7 | Jan 2 | Dec 31 | Dec 26 | Dec 20 | Dec 10 |
| 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 31 | Nov 3 | Nov 6 | Nov 10 | Nov 14 | Nov 17 | Nov 21 | Nov 25 | Dec 1 |
| 32°F | Nov 10 | Nov 17 | Nov 21 | Nov 27 | Dec 1 | Dec 3 | Dec 6 | Dec 12 | Dec 24 |
| 28°F | Nov 26 | Dec 1 | Dec 5 | Dec 11 | Dec 16 | Dec 22 | Jan 1 | Jan 5 | Jan 19 |
| 24°F | Dec 3 | Dec 8 | Dec 15 | Dec 21 | Dec 29 | Jan 1 | Jan 5 | Jan 13 | Jan 22 |
| 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 | 256 | 246 | 237 | 230 | 223 | 217 | 212 | 204 | 193 |
| 32°F | 319 | 304 | 295 | 287 | 279 | 272 | 264 | 257 | 244 |
| 28°F | 365 | 361 | 351 | 343 | 335 | 328 | 320 | 309 | 295 |
| 24°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 360 | 345 |
| 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
- 99% of years
- 28°F or colder
- 83% of years
- 24°F or colder
- 30% of years
- 20°F or colder
- 2% 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
- 2,627
- Cooling degree days, base 65°F
- 442
- Growing degree days, base 40°F
- 6,942
- Growing degree days, base 45°F
- 5,152
- Growing degree days, base 50°F
- 3,509
- Growing degree days, base 55°F
- 2,150
- Growing degree days, base 60°F
- 1,116
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 494 | 0 | 41 |
| February | 370 | 0 | 83 |
| March | 330 | 2 | 151 |
| April | 239 | 7 | 220 |
| May | 142 | 23 | 346 |
| June | 55 | 74 | 469 |
| July | 28 | 85 | 522 |
| August | 21 | 106 | 550 |
| September | 26 | 99 | 524 |
| October | 99 | 44 | 411 |
| November | 316 | 2 | 155 |
| December | 508 | 0 | 37 |
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 6.7 km from Fulton. 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 USC00047965 (Santa Rosa). Public domain.