San Luis Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Yuma Mcas. A median date has an even chance of a later freeze in spring, or an earlier one in fall.
A freeze (32°F or colder) happens in only 8 percent of years at Yuma Mcas, so there is no typical freeze season.
- Median at 36°F
- last January 6, 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 | Feb 6 | Jan 26 | Jan 16 | Jan 12 | Jan 6 | Jan 2 | Dec 29 | Dec 23 | Dec 14 |
| 32°F | – | – | – | – | – | – | – | – | – |
| 28°F | – | – | – | – | – | – | – | – | – |
| 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 | Dec 11 | Dec 15 | Dec 22 | Dec 26 | Dec 30 | Jan 1 | Jan 7 | Jan 15 | Jan 28 |
| 32°F | – | – | – | – | – | – | – | – | – |
| 28°F | – | – | – | – | – | – | – | – | – |
| 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 | 365 | 365 | 365 | 365 | 364 | 359 | 353 | 345 | 333 |
| 32°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 |
| 28°F | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 | 365 |
| 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
- 51% of years
- 32°F or colder
- 8% of years
- 28°F or colder
- 1% of years
- 24°F or colder
- 0% 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
- 679
- Cooling degree days, base 65°F
- 4,705
- Growing degree days, base 40°F
- 13,152
- Growing degree days, base 45°F
- 11,327
- Growing degree days, base 50°F
- 9,509
- Growing degree days, base 55°F
- 7,739
- Growing degree days, base 60°F
- 6,113
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 195 | 5 | 278 |
| February | 118 | 32 | 334 |
| March | 46 | 126 | 546 |
| April | 11 | 254 | 693 |
| May | 1 | 484 | 949 |
| June | 0 | 725 | 1,175 |
| July | 0 | 919 | 1,384 |
| August | 0 | 924 | 1,389 |
| September | 0 | 735 | 1,185 |
| October | 2 | 404 | 867 |
| November | 64 | 95 | 482 |
| December | 241 | 3 | 229 |
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 23.8 km from San Luis. 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 USW00003145 (Yuma Mcas). Public domain.