Harbor Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Brookings. 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 31 and the first fall freeze around December 27, a growing season of about 349 days.
- Median at 36°F
- last March 23, first December 7
- Median at 32°F
- last January 31, first December 27
- Median at 28°F
- last January 3, first December 30
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 26 | Apr 13 | Apr 4 | Mar 30 | Mar 23 | Mar 16 | Mar 5 | Feb 22 | Jan 31 |
| 32°F | Mar 21 | Mar 1 | Feb 23 | Feb 12 | Jan 31 | Jan 18 | Jan 1 | Dec 22 | Dec 9 |
| 28°F | Feb 16 | Feb 5 | Jan 24 | Jan 14 | Jan 3 | Dec 28 | Dec 23 | Dec 17 | Dec 8 |
| 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 14 | Nov 23 | Nov 28 | Dec 2 | Dec 7 | Dec 12 | Dec 19 | Jan 1 | Jan 30 |
| 32°F | Nov 26 | Dec 3 | Dec 10 | Dec 18 | Dec 27 | Jan 6 | Jan 25 | Feb 10 | Feb 27 |
| 28°F | Dec 1 | Dec 11 | Dec 19 | Dec 24 | Dec 30 | Jan 5 | Jan 21 | Jan 31 | Feb 14 |
| 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 | 320 | 298 | 282 | 271 | 259 | 250 | 240 | 230 | 214 |
| 32°F | 365 | 365 | 365 | 361 | 349 | 337 | 325 | 309 | 291 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 351 |
| 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
- 61% of years
- 28°F or colder
- 14% of years
- 24°F or colder
- 2% 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
- 4,080
- Cooling degree days, base 65°F
- 28
- Growing degree days, base 40°F
- 5,078
- Growing degree days, base 45°F
- 3,314
- Growing degree days, base 50°F
- 1,796
- Growing degree days, base 55°F
- 729
- Growing degree days, base 60°F
- 179
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 507 | 0 | 36 |
| February | 449 | 0 | 38 |
| March | 484 | 0 | 43 |
| April | 407 | 0 | 71 |
| May | 315 | 1 | 155 |
| June | 209 | 2 | 243 |
| July | 159 | 4 | 310 |
| August | 158 | 6 | 313 |
| September | 172 | 10 | 288 |
| October | 285 | 5 | 190 |
| November | 404 | 0 | 80 |
| December | 532 | 0 | 29 |
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 1.8 km from Harbor. 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 USC00351058 (Brookings). Public domain.