Three Rivers Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Sunriver. A median date has an even chance of a later freeze in spring, or an earlier one in fall.
NOAA does not state freeze dates for this station.
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 | – | – | – | – | – | – | – | – | – |
| 32°F | – | – | – | – | – | – | – | – | – |
| 28°F | – | – | – | – | – | – | – | – | – |
| 24°F | Jun 15 | May 31 | May 26 | May 18 | May 15 | May 11 | May 8 | May 5 | May 1 |
| 20°F | May 10 | May 5 | May 3 | May 1 | Apr 29 | Apr 27 | Apr 25 | Apr 21 | Apr 14 |
| 16°F | Apr 30 | Apr 27 | Apr 23 | Apr 19 | Apr 15 | Apr 10 | Apr 3 | Mar 26 | Mar 11 |
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 | – | – | – | – | – | – | – | – | – |
| 32°F | – | – | – | – | – | – | – | – | – |
| 28°F | – | – | – | – | – | – | – | – | – |
| 24°F | Sep 8 | Sep 15 | Sep 20 | Sep 24 | Sep 28 | Oct 1 | Oct 4 | Oct 8 | Oct 14 |
| 20°F | Sep 23 | Sep 30 | Oct 5 | Oct 8 | Oct 13 | Oct 17 | Oct 21 | Oct 27 | Nov 1 |
| 16°F | Oct 10 | Oct 17 | Oct 23 | Oct 27 | Nov 1 | Nov 4 | Nov 9 | Nov 15 | Nov 21 |
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 | 34 | 28 | 24 | 22 | 19 | 17 | 15 | 14 | 12 |
| 32°F | 71 | 61 | 54 | 48 | 42 | 38 | 33 | 29 | 24 |
| 28°F | 112 | 103 | 95 | 89 | 82 | 75 | 68 | 61 | 51 |
| 24°F | 157 | 148 | 142 | 136 | 130 | 125 | 119 | 111 | 99 |
| 20°F | 193 | 183 | 177 | 172 | 168 | 163 | 157 | 150 | 141 |
| 16°F | 236 | 223 | 213 | 206 | 200 | 194 | 188 | 182 | 174 |
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
- 100% of years
- 28°F or colder
- 100% of years
- 24°F or colder
- 100% of years
- 20°F or colder
- 100% of years
- 16°F or colder
- 100% 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
- 7,661
- Cooling degree days, base 65°F
- 85
- Growing degree days, base 40°F
- 2,916
- Growing degree days, base 45°F
- 1,972
- Growing degree days, base 50°F
- 1,234
- Growing degree days, base 55°F
- 676
- Growing degree days, base 60°F
- 296
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 1,094 | 0 | 0 |
| February | 921 | 0 | 0 |
| March | 870 | 0 | 1 |
| April | 732 | 0 | 11 |
| May | 504 | 2 | 81 |
| June | 318 | 6 | 172 |
| July | 116 | 40 | 391 |
| August | 137 | 31 | 363 |
| September | 310 | 7 | 183 |
| October | 625 | 0 | 31 |
| November | 896 | 0 | 2 |
| December | 1,139 | 0 | 0 |
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 9.4 km from Three Rivers. 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 USC00358246 (Sunriver). Public domain.