Dilley Frost Dates and Growing Season
Frost and the growing season
NOAA's 1991-2020 freeze probabilities for Dilley. 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 16 and the first fall freeze around December 6, a growing season of about 296 days.
- Median at 36°F
- last March 2, first November 23
- Median at 32°F
- last February 16, first December 6
- Median at 28°F
- last January 26, first December 23
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 22 | Mar 16 | Mar 11 | Mar 6 | Mar 2 | Feb 27 | Feb 22 | Feb 16 | Feb 6 |
| 32°F | Mar 12 | Mar 4 | Feb 28 | Feb 21 | Feb 16 | Feb 8 | Feb 1 | Jan 26 | Jan 14 |
| 28°F | Mar 1 | Feb 19 | Feb 10 | Feb 2 | Jan 26 | Jan 16 | Jan 7 | Dec 30 | Dec 19 |
| 24°F | Feb 16 | Feb 7 | Jan 25 | Jan 16 | Jan 6 | Jan 1 | Dec 28 | Dec 19 | Dec 12 |
| 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 5 | Nov 11 | Nov 16 | Nov 20 | Nov 23 | Nov 28 | Dec 1 | Dec 5 | Dec 11 |
| 32°F | Nov 16 | Nov 23 | Nov 28 | Dec 3 | Dec 6 | Dec 11 | Dec 16 | Dec 24 | Jan 3 |
| 28°F | Dec 1 | Dec 6 | Dec 12 | Dec 17 | Dec 23 | Dec 29 | Jan 4 | Jan 17 | Feb 4 |
| 24°F | Dec 9 | Dec 14 | Dec 21 | Dec 27 | Jan 1 | Jan 3 | Jan 13 | Jan 24 | Feb 7 |
| 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 | 295 | 285 | 277 | 272 | 266 | 261 | 255 | 248 | 238 |
| 32°F | 336 | 324 | 312 | 304 | 296 | 289 | 280 | 272 | 261 |
| 28°F | 365 | 361 | 351 | 343 | 336 | 328 | 317 | 309 | 297 |
| 24°F | 365 | 365 | 365 | 365 | 365 | 364 | 355 | 344 | 329 |
| 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
- 99% of years
- 28°F or colder
- 83% of years
- 24°F or colder
- 38% of years
- 20°F or colder
- 9% of years
- 16°F or colder
- 1% 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
- 1,243
- Cooling degree days, base 65°F
- 3,456
- Growing degree days, base 40°F
- 11,354
- Growing degree days, base 45°F
- 9,565
- Growing degree days, base 50°F
- 7,844
- Growing degree days, base 55°F
- 6,233
- Growing degree days, base 60°F
- 4,763
Growing degree days by month, base 50°F
Heating and cooling by month
| Month | Heating DD | Cooling DD | Growing DD 50 |
|---|---|---|---|
| January | 361 | 11 | 174 |
| February | 224 | 29 | 250 |
| March | 109 | 103 | 467 |
| April | 24 | 227 | 653 |
| May | 1 | 426 | 890 |
| June | 0 | 564 | 1,014 |
| July | 0 | 632 | 1,097 |
| August | 0 | 648 | 1,113 |
| September | 1 | 469 | 918 |
| October | 27 | 261 | 700 |
| November | 158 | 73 | 378 |
| December | 339 | 15 | 192 |
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 Dilley. 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 USC00412458 (Dilley). Public domain.