Alpine Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Alpine. 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 12 and the first fall freeze around December 24, a growing season of about 317 days.
- Median at 36°F
- last March 17, first December 7
- Median at 32°F
- last February 12, first December 24
- Median at 28°F
- last January 22, first January 4
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 16 | Apr 7 | Mar 31 | Mar 24 | Mar 17 | Mar 11 | Mar 3 | Feb 25 | Feb 15 |
| 32°F | Mar 20 | Mar 4 | Feb 26 | Feb 19 | Feb 12 | Feb 4 | Jan 27 | Jan 10 | Dec 29 |
| 28°F | Feb 23 | Feb 12 | Feb 4 | Jan 29 | Jan 22 | Jan 8 | Dec 31 | Dec 22 | Dec 12 |
| 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 24 | Nov 29 | Dec 2 | Dec 7 | Dec 10 | Dec 13 | Dec 17 | Dec 23 |
| 32°F | Dec 2 | Dec 10 | Dec 14 | Dec 19 | Dec 24 | Dec 28 | Jan 1 | Jan 19 | Feb 3 |
| 28°F | Dec 10 | Dec 15 | Dec 25 | Dec 31 | Jan 4 | Jan 15 | Jan 27 | Feb 6 | Feb 20 |
| 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 | 301 | 288 | 276 | 269 | 263 | 256 | 248 | 240 | 229 |
| 32°F | 364 | 350 | 339 | 329 | 317 | 308 | 300 | 287 | 272 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 365 | 359 | 342 | 317 |
| 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
- 90% of years
- 28°F or colder
- 38% of years
- 24°F or colder
- 6% of years
- 20°F or colder
- 1% 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
- 2,028
- Cooling degree days, base 65°F
- 1,167
- Growing degree days, base 40°F
- 8,265
- Growing degree days, base 45°F
- 6,460
- Growing degree days, base 50°F
- 4,757
- Growing degree days, base 55°F
- 3,270
- Growing degree days, base 60°F
- 2,063
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 367 | 1 | 135 |
| February | 332 | 3 | 123 |
| March | 291 | 6 | 197 |
| April | 207 | 21 | 271 |
| May | 120 | 46 | 391 |
| June | 31 | 113 | 533 |
| July | 2 | 264 | 727 |
| August | 1 | 328 | 792 |
| September | 9 | 252 | 693 |
| October | 72 | 108 | 501 |
| November | 203 | 26 | 280 |
| December | 394 | 1 | 114 |
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 1.1 km from Alpine. 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 USC00040136 (Alpine). Public domain.