USDA Hardiness Zone 9b
Frost Dates for 92508 — Riverside, California
NOAA 1991–2020 normals from Riverside Fire Stn 3, CA (840 ft), 6 miles northwest.
Updated
A freeze (32°F) reaches Riverside in 69% of winters. When it does, the first fall frost comes around December 25 and the last spring frost around January 9; after February 25 the chance of another is under 7%.
- Last spring frost
- January 9
- First fall frost
- December 25
- Winters with a freeze
- 69%
- Hardiness zone
- 9b
50%, in freezing years
50%, in freezing years
32°F or below, 1991–2020
25 to 30°F (-3.9 to -1.1°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 19 observed
NOAA normal
Frost risk by date in Riverside
In the 69% of winters that bring a 32°F night, half of springs at Riverside Fire Stn 3, CA see their last 32°F night by January 9; only one in ten is past it by December 16, and one in ten still has one after February 25. Counting the winters with no freeze at all, the risk of a 32°F night after February 25 is under 7% and after January 9 34%. The 47 days between the even-odds date and the one-in-ten date is wider than at 96% 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 25 in half of years, as early as December 1 one year in ten, and holds off past January 27 one year in ten. A hard freeze of 28°F is less common: it came in 11% of winters. The freeze-free season lasts 353 days in a typical year, longer than at 95% of the 219 California stations; it reaches 365 days one year in ten and falls short of 307 one year in ten. On average 2 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 41 days longer, to about February 19, and return around December 6. A 24°F night is unusual: 1% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F99% of yrs | Jan 8 | Jan 21 | Feb 2 | Feb 10 | Feb 19 | Feb 27 | Mar 4 | Mar 11 | Mar 22 |
| 32°F69% of yrs | Dec 16 | Dec 25 | Dec 31 | Jan 4 | Jan 9 | Jan 17 | Jan 25 | Feb 6 | Feb 25 |
| 28°F11% of yrs | too rare for a date | ||||||||
| 24°F1% of yrs | too rare for a date | ||||||||
| 20°F0% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F99% of yrs | Nov 15 | Nov 24 | Nov 29 | Dec 2 | Dec 6 | Dec 11 | Dec 15 | Dec 21 | Jan 1 |
| 32°F69% of yrs | Dec 1 | Dec 10 | Dec 15 | Dec 20 | Dec 25 | Dec 30 | Jan 4 | Jan 11 | Jan 27 |
| 28°F11% of yrs | too rare for a date | ||||||||
| 24°F1% of yrs | too rare for a date | ||||||||
| 20°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Riverside Fire Stn 3, 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 92508 →Compare Riverside with another place →
Weather by month in Riverside
August is the warmest month at Riverside Fire Stn 3, CA, averaging 97°F by day and 65°F at night; December is the coldest at 69°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 13% of years.
Warmth for growing adds up to 6,222 growing degree days a year (base 50°F), more than at 95% of the 283 California stations. 39% of them (2,408) have built up by the end of June, and August adds the most, 950. Precipitation totals 10.1 inches a year, most in February (2.5") and least in June (0.1"); May to September bring 7% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 70 | 43 | 2.2 | 36% | 1 | 207 |
| Feb | 70 | 44 | 2.5 | 13% | <1 | 199 |
| Mar | 73 | 46 | 1.6 | 5% | <1 | 302 |
| Apr | 78 | 50 | 0.6 | 0% | 0 | 419 |
| May | 81 | 55 | 0.2 | 0% | 0 | 560 |
| Jun | 89 | 59 | 0.1 | 0% | 0 | 722 |
| Jul | 95 | 64 | 0.1 | 0% | 0 | 915 |
| Aug | 97 | 65 | 0.1 | 0% | 0 | 950 |
| Sep | 93 | 62 | 0.2 | 0% | 0 | 822 |
| Oct | 84 | 55 | 0.4 | 0% | 0 | 601 |
| Nov | 76 | 47 | 0.7 | 6% | <1 | 343 |
| Dec | 69 | 42 | 1.4 | 40% | 1 | 184 |
Monthly normals 1991–2020 at Riverside Fire Stn 3, CA (840 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, Riverside Citrus Exp, CA, 6 miles northwest of Riverside, has a 32°F night in 45% of winters against 69% here, and a coolest-month low 1°F warmer (43°F).
When it snows in Riverside, California
Measurable snow is rare here: only 0 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at Riverside Fire Stn 3, CA, 5.7 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 92508 is 6 miles from Riverside Fire Stn 3, CA, which stands at 840 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 92504 (Riverside). The 2023 USDA Plant Hardiness Zone Map lists ZIP 92508 in zone 9b, the band where the coldest night of the year averaged 25 to 30°F (-3.9 to -1.1°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.