Sunol Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Fremont. 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 7 and the first fall freeze around December 22, a growing season of about 353 days.
- Median at 36°F
- last February 6, first December 5
- Median at 32°F
- last January 7, first December 22
- 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 | Mar 11 | Mar 1 | Feb 24 | Feb 14 | Feb 6 | Jan 31 | Jan 25 | Jan 16 | Jan 3 |
| 32°F | Feb 7 | Jan 29 | Jan 22 | Jan 13 | Jan 7 | Jan 2 | Dec 29 | Dec 23 | Dec 14 |
| 28°F | Jan 20 | Jan 13 | Jan 7 | Jan 2 | Dec 31 | Dec 29 | Dec 25 | Dec 20 | Dec 13 |
| 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 17 | Nov 24 | Nov 30 | Dec 2 | Dec 5 | Dec 9 | Dec 13 | Dec 21 | Jan 2 |
| 32°F | Dec 2 | Dec 7 | Dec 12 | Dec 16 | Dec 22 | Dec 27 | Jan 1 | Jan 7 | Jan 21 |
| 28°F | Dec 11 | Dec 18 | Dec 21 | Dec 26 | Dec 29 | Jan 1 | Jan 5 | Jan 9 | Jan 17 |
| 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 | 338 | 326 | 317 | 309 | 301 | 292 | 284 | 275 | 263 |
| 32°F | 365 | 365 | 365 | 361 | 353 | 347 | 339 | 334 | 323 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 362 |
| 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
- 98% of years
- 32°F or colder
- 65% of years
- 28°F or colder
- 14% of years
- 24°F or colder
- 0% 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
- 2,374
- Cooling degree days, base 65°F
- 391
- Growing degree days, base 40°F
- 7,143
- Growing degree days, base 45°F
- 5,332
- Growing degree days, base 50°F
- 3,622
- Growing degree days, base 55°F
- 2,170
- Growing degree days, base 60°F
- 1,085
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 446 | 0 | 63 |
| February | 339 | 0 | 101 |
| March | 289 | 2 | 185 |
| April | 218 | 8 | 241 |
| May | 133 | 25 | 357 |
| June | 56 | 56 | 450 |
| July | 15 | 88 | 538 |
| August | 11 | 93 | 547 |
| September | 24 | 88 | 515 |
| October | 103 | 31 | 392 |
| November | 289 | 1 | 171 |
| December | 451 | 0 | 63 |
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 12.6 km from Sunol. 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 USC00043244 (Fremont). Public domain.