Boulder City Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Alan Bible Visitor Ctr. 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 21 and the first fall freeze around December 17, a growing season of about 328 days.
- Median at 36°F
- last February 13, first December 5
- Median at 32°F
- last January 21, first December 17
- Median at 28°F
- last January 10, 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 | Mar 13 | Mar 4 | Feb 25 | Feb 19 | Feb 13 | Feb 6 | Feb 1 | Jan 27 | Jan 18 |
| 32°F | Mar 5 | Feb 20 | Feb 8 | Jan 29 | Jan 21 | Jan 16 | Jan 11 | Jan 5 | Dec 29 |
| 28°F | Mar 3 | Feb 17 | Jan 26 | Jan 16 | Jan 10 | Jan 5 | Jan 1 | Dec 27 | Dec 19 |
| 24°F | Mar 2 | Feb 16 | Feb 2 | Jan 17 | Jan 11 | Jan 3 | Dec 31 | Dec 24 | Dec 19 |
| 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 23 | Nov 28 | Dec 1 | Dec 3 | Dec 5 | Dec 8 | Dec 11 | Dec 14 | Dec 18 |
| 32°F | Dec 2 | Dec 6 | Dec 9 | Dec 13 | Dec 17 | Dec 20 | Dec 24 | Dec 27 | Jan 3 |
| 28°F | Dec 8 | Dec 14 | Dec 21 | Dec 26 | Dec 30 | Jan 2 | Jan 7 | Jan 16 | Feb 3 |
| 24°F | Dec 15 | Dec 20 | Dec 28 | Jan 1 | Jan 5 | Jan 11 | Jan 15 | Feb 9 | Mar 1 |
| 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 | 322 | 313 | 307 | 301 | 295 | 289 | 283 | 274 | 264 |
| 32°F | 355 | 347 | 340 | 334 | 328 | 320 | 312 | 301 | 285 |
| 28°F | 365 | 365 | 365 | 365 | 360 | 353 | 346 | 335 | 314 |
| 24°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 350 |
| 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
- 98% of years
- 28°F or colder
- 63% of years
- 24°F or colder
- 21% of years
- 20°F or colder
- 5% 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
- 1,616
- Cooling degree days, base 65°F
- 4,083
- Growing degree days, base 40°F
- 11,597
- Growing degree days, base 45°F
- 9,805
- Growing degree days, base 50°F
- 8,112
- Growing degree days, base 55°F
- 6,593
- Growing degree days, base 60°F
- 5,256
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 459 | 0 | 68 |
| February | 294 | 2 | 156 |
| March | 138 | 54 | 385 |
| April | 32 | 170 | 588 |
| May | 3 | 425 | 887 |
| June | 0 | 748 | 1,198 |
| July | 0 | 951 | 1,417 |
| August | 0 | 877 | 1,342 |
| September | 0 | 612 | 1,062 |
| October | 22 | 224 | 667 |
| November | 192 | 21 | 285 |
| December | 477 | 0 | 58 |
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 4.7 km from Boulder City. 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 USC00260125 (Alan Bible Visitor Ctr). Public domain.