Frost dates for Rancho Cucamonga, California
California · first & last freeze, from NOAA 1991–2020 climate normals
In a typical year, the last spring freeze around Rancho Cucamonga comes near January 4 and the first fall freeze near December 30. One year in ten, a freeze still arrives after February 7 in spring — and one year in ten, the first fall freeze has already landed by December 11. NCEI's own growing-season statistic (days between freezes, percentiled per year) puts the median at 365 days.
Freeze-date probabilities, three thresholds
| Threshold | Last spring — 9 in 10 years past by | Last spring — typical (median) | Last spring — 1 in 10 years later than | First fall — 1 in 10 years by | First fall — typical (median) | First fall — 9 in 10 years by |
|---|---|---|---|---|---|---|
| 36°F — near-freezing (frost can occur) | December 24 | January 27 | February 28 | November 27 | December 17 | January 17 |
| 32°F — freezing | December 14 | January 4 | February 7 | December 11 | December 30 | February 1 |
| 28°F — hard freeze | reaches this temperature in only 4% of years — too rare for NCEI to compute dates | |||||
Measured at Ontario Intl Ap, CA (USW00003102), 5.5 mi from the city's census reference point, elev. 949 ft. NOAA/NCEI 1991–2020 normals. Read each date column as odds over the 30-year record — e.g. "9 in 10 years past by" means only one spring in ten saw a later freeze than that date.
Frost-free windows (computed)
| Window (32°F ends) | Opens | Closes | Length |
|---|---|---|---|
| Cautious (1-in-10 freeze risk at each end) | February 7 | December 11 | 307 days |
| Typical (median freeze dates) | January 4 | December 30 | 360 days |
| Gambler's (9-in-10 freeze risk at each end) | December 14 | February 1 | 365 days (effectively year-round at this risk level) |
Pure arithmetic on the freeze-date percentiles above — the "cautious" window opens on the date only 1 year in 10 still sees a later spring freeze, and closes on the date by which only 1 year in 10 has already frozen.
About this city's numbers
- Census entity: Rancho Cucamonga city, California — official 2024 population estimate 176,675.
- Weather station: Ontario Intl Ap, CA (USW00003102), 5.5 mi from the city's census-gazetteer reference point at elevation 949 ft. Frost dates are that station's history — neighborhoods vary.
- Data pulled 2026-09-05; normals period 1991-2020 (replaced by NOAA roughly once a decade).
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