Novato Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for San Rafael Civic Ctr. 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 January 11 and the first fall freeze around December 21, a growing season of about 349 days.
- Median at 36°F
- last February 22, first December 5
- Median at 32°F
- last January 11, first December 21
- Median at 28°F
- last December 31, first December 29
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 6 | Mar 20 | Mar 6 | Feb 27 | Feb 22 | Feb 13 | Feb 4 | Jan 23 | Jan 6 |
| 32°F | Feb 25 | Feb 14 | Feb 1 | Jan 21 | Jan 11 | Jan 3 | Dec 30 | Dec 23 | Dec 14 |
| 28°F | Feb 21 | Feb 10 | Jan 22 | Jan 8 | Dec 31 | Dec 27 | Dec 23 | Dec 18 | Dec 11 |
| 24°F | – | – | – | – | – | – | – | – | – |
| 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 | Nov 15 | Nov 23 | Nov 28 | Dec 1 | Dec 5 | Dec 8 | Dec 13 | Dec 20 | Jan 1 |
| 32°F | Dec 2 | Dec 8 | Dec 13 | Dec 17 | Dec 21 | Dec 27 | Jan 2 | Jan 12 | Feb 9 |
| 28°F | Dec 7 | Dec 14 | Dec 20 | Dec 25 | Dec 29 | Jan 2 | Jan 16 | Feb 3 | Feb 18 |
| 24°F | – | – | – | – | – | – | – | – | – |
| 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 | 332 | 318 | 308 | 298 | 287 | 278 | 271 | 259 | 241 |
| 32°F | 365 | 365 | 365 | 357 | 349 | 341 | 334 | 320 | 304 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 349 |
| 24°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 |
| 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
- 99% of years
- 32°F or colder
- 70% of years
- 28°F or colder
- 21% of years
- 24°F or colder
- 3% of years
- 20°F or colder
- 0% 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
- 2,481
- Cooling degree days, base 65°F
- 486
- Growing degree days, base 40°F
- 7,133
- Growing degree days, base 45°F
- 5,335
- Growing degree days, base 50°F
- 3,652
- Growing degree days, base 55°F
- 2,245
- Growing degree days, base 60°F
- 1,184
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 473 | 0 | 52 |
| February | 349 | 0 | 96 |
| March | 306 | 1 | 170 |
| April | 228 | 8 | 231 |
| May | 146 | 31 | 351 |
| June | 54 | 75 | 471 |
| July | 19 | 109 | 555 |
| August | 14 | 119 | 570 |
| September | 25 | 101 | 527 |
| October | 98 | 40 | 408 |
| November | 293 | 2 | 170 |
| December | 477 | 0 | 51 |
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 12.4 km from Novato. 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 USC00047880 (San Rafael Civic Ctr). Public domain.