North Gate Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Mt Diablo Junction. 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 8 and the first fall freeze around December 22, a growing season of about 282 days.
- Median at 36°F
- last April 19, first November 29
- Median at 32°F
- last March 8, first December 22
- Median at 28°F
- last February 8, first January 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 | May 20 | May 10 | May 1 | Apr 25 | Apr 19 | Apr 13 | Apr 7 | Mar 30 | Mar 16 |
| 32°F | Apr 15 | Apr 5 | Mar 28 | Mar 19 | Mar 8 | Feb 27 | Feb 18 | Jan 31 | Jan 12 |
| 28°F | Mar 23 | Mar 3 | Feb 26 | Feb 19 | Feb 8 | Jan 30 | Jan 14 | Jan 4 | Dec 21 |
| 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 6 | Nov 14 | Nov 19 | Nov 25 | Nov 29 | Dec 2 | Dec 6 | Dec 12 | Dec 20 |
| 32°F | Nov 23 | Dec 1 | Dec 9 | Dec 15 | Dec 22 | Jan 1 | Jan 8 | Jan 22 | Feb 11 |
| 28°F | Dec 8 | Dec 20 | Dec 30 | Jan 4 | Jan 16 | Jan 29 | Feb 10 | Feb 22 | Mar 3 |
| 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 | 264 | 250 | 238 | 229 | 221 | 214 | 207 | 197 | 183 |
| 32°F | 343 | 322 | 306 | 291 | 282 | 273 | 264 | 253 | 238 |
| 28°F | 365 | 365 | 365 | 365 | 364 | 348 | 328 | 307 | 286 |
| 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
- 100% of years
- 32°F or colder
- 96% of years
- 28°F or colder
- 50% of years
- 24°F or colder
- 7% 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
- 3,309
- Cooling degree days, base 65°F
- 925
- Growing degree days, base 40°F
- 6,774
- Growing degree days, base 45°F
- 5,097
- Growing degree days, base 50°F
- 3,645
- Growing degree days, base 55°F
- 2,484
- Growing degree days, base 60°F
- 1,591
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 536 | 0 | 54 |
| February | 472 | 0 | 57 |
| March | 454 | 1 | 97 |
| April | 363 | 9 | 145 |
| May | 244 | 44 | 280 |
| June | 100 | 120 | 471 |
| July | 24 | 241 | 682 |
| August | 21 | 235 | 679 |
| September | 45 | 190 | 596 |
| October | 145 | 78 | 403 |
| November | 358 | 8 | 143 |
| December | 547 | 0 | 39 |
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 6.6 km from North Gate. 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 USC00045915 (Mt Diablo Junction). Public domain.