Bunker Hill Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for North Bend Rgnl AP. 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 21 and the first fall freeze around December 9, a growing season of about 294 days.
- Median at 36°F
- last April 2, first November 15
- Median at 32°F
- last February 21, first December 9
- Median at 28°F
- last January 4, first December 22
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 1 | Apr 23 | Apr 16 | Apr 8 | Apr 2 | Mar 29 | Mar 24 | Mar 15 | Mar 1 |
| 32°F | Mar 25 | Mar 14 | Mar 5 | Feb 26 | Feb 21 | Feb 13 | Feb 6 | Jan 26 | Dec 31 |
| 28°F | Feb 22 | Feb 14 | Feb 1 | Jan 18 | Jan 4 | Dec 29 | Dec 22 | Dec 13 | Dec 3 |
| 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 | Oct 24 | Oct 31 | Nov 5 | Nov 10 | Nov 15 | Nov 19 | Nov 25 | Dec 1 | Dec 11 |
| 32°F | Nov 12 | Nov 21 | Nov 27 | Dec 2 | Dec 9 | Dec 16 | Dec 25 | Jan 4 | Jan 28 |
| 28°F | Nov 25 | Dec 5 | Dec 10 | Dec 15 | Dec 22 | Dec 30 | Jan 10 | Jan 28 | Feb 15 |
| 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 | 263 | 249 | 239 | 231 | 224 | 216 | 210 | 200 | 188 |
| 32°F | 340 | 324 | 313 | 304 | 294 | 284 | 275 | 265 | 251 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 355 | 342 | 331 | 312 |
| 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
- 95% of years
- 28°F or colder
- 44% 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
- 4,369
- Cooling degree days, base 65°F
- 8
- Growing degree days, base 40°F
- 4,780
- Growing degree days, base 45°F
- 3,063
- Growing degree days, base 50°F
- 1,631
- Growing degree days, base 55°F
- 644
- Growing degree days, base 60°F
- 123
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 550 | 0 | 25 |
| February | 489 | 0 | 26 |
| March | 512 | 0 | 32 |
| April | 440 | 0 | 49 |
| May | 334 | 0 | 138 |
| June | 230 | 1 | 221 |
| July | 161 | 1 | 305 |
| August | 143 | 2 | 324 |
| September | 183 | 3 | 270 |
| October | 314 | 1 | 159 |
| November | 446 | 0 | 59 |
| December | 569 | 0 | 23 |
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 7.1 km from Bunker Hill. 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 USW00024284 (North Bend Rgnl AP). Public domain.