Shasta Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Whiskeytown Rsvr. 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 13 and the first fall freeze around December 13, a growing season of about 304 days.
- Median at 36°F
- last March 27, first November 26
- Median at 32°F
- last February 13, first December 13
- Median at 28°F
- last January 3, first December 25
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 20 | Apr 12 | Apr 6 | Apr 1 | Mar 27 | Mar 20 | Mar 11 | Mar 1 | Feb 18 |
| 32°F | Mar 25 | Mar 8 | Feb 28 | Feb 21 | Feb 13 | Feb 5 | Jan 26 | Jan 13 | Dec 30 |
| 28°F | Feb 18 | Feb 5 | Jan 25 | Jan 13 | Jan 3 | Dec 30 | Dec 24 | Dec 15 | Dec 7 |
| 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 13 | Nov 17 | Nov 21 | Nov 26 | Nov 30 | Dec 2 | Dec 7 | Dec 15 |
| 32°F | Nov 20 | Nov 28 | Dec 3 | Dec 8 | Dec 13 | Dec 18 | Dec 25 | Jan 1 | Jan 19 |
| 28°F | Nov 30 | Dec 7 | Dec 11 | Dec 18 | Dec 25 | Dec 31 | Jan 5 | Jan 17 | Feb 9 |
| 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 | 283 | 269 | 259 | 252 | 245 | 237 | 230 | 221 | 208 |
| 32°F | 349 | 334 | 324 | 313 | 304 | 295 | 284 | 272 | 259 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 355 | 344 | 336 | 323 |
| 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
- 49% of years
- 24°F or colder
- 8% 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
- 2,752
- Cooling degree days, base 65°F
- 2,006
- Growing degree days, base 40°F
- 8,398
- Growing degree days, base 45°F
- 6,691
- Growing degree days, base 50°F
- 5,188
- Growing degree days, base 55°F
- 3,929
- Growing degree days, base 60°F
- 2,879
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 567 | 0 | 31 |
| February | 434 | 0 | 64 |
| March | 367 | 4 | 148 |
| April | 223 | 28 | 267 |
| May | 79 | 144 | 531 |
| June | 18 | 326 | 758 |
| July | 1 | 546 | 1,010 |
| August | 0 | 507 | 972 |
| September | 7 | 348 | 790 |
| October | 100 | 100 | 467 |
| November | 369 | 3 | 127 |
| December | 587 | 0 | 22 |
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 3.4 km from Shasta. 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 USC00049621 (Whiskeytown Rsvr). Public domain.