USDA Hardiness Zone 10a
Frost Dates for 91767 — Pomona, California
NOAA 1991–2020 normals from Pomona/Fairplex, CA (999 ft), 2 miles west.
Updated
A freeze (32°F) reaches Pomona in 65% of winters. When it does, the first fall frost comes around December 28 and the last spring frost around January 8; after February 18 the chance of another is under 7%.
- Last spring frost
- January 8
- First fall frost
- December 28
- Winters with a freeze
- 65%
- Hardiness zone
- 10a
50%, in freezing years
50%, in freezing years
32°F or below, 1991–2020
30 to 35°F (-1.1 to 1.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 17 observed
NOAA normal
Frost risk by date in Pomona
In the 65% of winters that bring a 32°F night, half of springs at Pomona/Fairplex, CA see their last 32°F night by January 8; only one in ten is past it by December 14, and one in ten still has one after February 18. Counting the winters with no freeze at all, the risk of a 32°F night after February 18 is under 7% and after January 8 33%. The 41 days between the even-odds date and the one-in-ten date is wider than at 89% of the 220 California stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by December 28 in half of years, as early as December 5 one year in ten, and holds off past February 2 one year in ten. A hard freeze of 28°F is less common: it came in 7% of winters. The freeze-free season lasts 354 days in a typical year, longer than at 97% of the 219 California stations; it reaches 365 days one year in ten and falls short of 315 one year in ten. On average 3 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 31 days longer, to about February 8, and return around December 10. No night reached 24°F in 1991–2020.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F99% of yrs | Dec 29 | Jan 9 | Jan 22 | Jan 31 | Feb 8 | Feb 16 | Feb 24 | Mar 1 | Mar 9 |
| 32°F65% of yrs | Dec 14 | Dec 24 | Dec 29 | Jan 1 | Jan 8 | Jan 15 | Jan 26 | Feb 4 | Feb 18 |
| 28°F7% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F99% of yrs | Nov 21 | Nov 28 | Dec 3 | Dec 7 | Dec 10 | Dec 13 | Dec 16 | Dec 20 | Dec 26 |
| 32°F65% of yrs | Dec 5 | Dec 13 | Dec 19 | Dec 24 | Dec 28 | Dec 31 | Jan 4 | Jan 14 | Feb 2 |
| 28°F7% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Pomona/Fairplex, CA, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 91767 →Compare Pomona with another place →
Weather by month in Pomona
August is the warmest month at Pomona/Fairplex, CA, averaging 92°F by day and 63°F at night; December is the coldest at 67°F and 42°F. From March to November the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 14% of years.
Warmth for growing adds up to 5,557 growing degree days a year (base 50°F), more than at 81% of the 283 California stations. 39% of them (2,164) have built up by the end of June, and August adds the most, 854. Precipitation totals 14.5 inches a year, most in February (4.2") and least in July (0.0"); May to September bring 2% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 68 | 43 | 2.9 | 29% | 1 | 183 |
| Feb | 67 | 45 | 4.2 | 14% | <1 | 177 |
| Mar | 72 | 47 | 2.1 | 1% | <1 | 298 |
| Apr | 76 | 50 | 1.0 | 0% | 0 | 381 |
| May | 78 | 54 | 0.2 | 0% | 0 | 502 |
| Jun | 84 | 57 | 0.1 | 0% | 0 | 623 |
| Jul | 90 | 62 | 0.0 | 0% | 0 | 815 |
| Aug | 92 | 63 | 0.0 | 0% | 0 | 854 |
| Sep | 89 | 60 | 0.0 | 0% | 0 | 737 |
| Oct | 81 | 54 | 1.0 | 0% | 0 | 533 |
| Nov | 74 | 47 | 0.7 | 4% | <1 | 310 |
| Dec | 67 | 42 | 2.3 | 38% | 1 | 144 |
Monthly normals 1991–2020 at Pomona/Fairplex, CA (999 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Ontario International Airport, CA, 8 miles east of Pomona, has a 32°F night in 41% of winters against 65% here, and a coolest-month low 2°F warmer (44°F).
When it snows in Pomona, California
Measurable snow is rare here: only 0 of 17 winters from 1991 to 2020 recorded 0.1 inch or more at Glendora Fc 287b, CA, 7.7 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 91767 is 2 miles from Pomona/Fairplex, CA, which stands at 999 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 16 other ZIP codes share the station; its figures are presented in full for 91766 (Pomona). The 2023 USDA Plant Hardiness Zone Map lists ZIP 91767 in zone 10a, the band where the coldest night of the year averaged 30 to 35°F (-1.1 to 1.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across California →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.