Frost history / Portola, CA
Portola, CA: frost dates by year
Last spring and first fall frost at NOAA station USC00047085, 1951 to 2025, measured from daily minimum temperatures.
Elevation 4,850 ft, 39.805, -120.472. Download the data (JSON) · NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | Jun 19 | Sep 1 |
| Earliest | May 11 (2023) | Aug 1 (1953) |
| Latest | Jul 31 (1961) | Oct 9 (2001) |
| Trend | 5.5 days earlier per decade | 6.1 days later per decade |
| Years with data | 61 | 58 |
At 28°F (hard freeze) the median last spring date is May 29 and the median first fall date is Sep 23.
The trend is a straight-line fit through the years with a freeze. A positive spring trend means the last frost now comes later. Short or patchy records give noisy trends.
Chart
Last spring frost (32°F)
First fall frost (32°F)
Dots are single years. The gray line is the median, the green line the fitted trend.
Year by year
| Year | Last spring 32°F | First fall 32°F | Last spring 28°F | First fall 28°F |
|---|---|---|---|---|
| 2025 | Jun 23 | Oct 6 | Apr 24 | Oct 12 |
| 2024 | Jun 18 | Sep 18 | May 8 | Oct 19 |
| 2023 | May 11 | Sep 13 | Apr 20 | Oct 12 |
| 2022 | no data | Sep 15 | no data | Oct 22 |
| 2021 | Jun 10 | no data | Jun 10 | no data |
| 2020 | Jun 18 | Sep 18 | May 23 | Oct 22 |
| 2018 | Jun 12 | no data | May 3 | no data |
| 2017 | Jun 13 | Sep 23 | May 18 | Sep 23 |
| 2016 | May 23 | Sep 4 | May 23 | Sep 23 |
| 2015 | May 21 | Sep 4 | May 12 | Oct 23 |
| 2014 | Jun 18 | Sep 26 | May 12 | Sep 26 |
| 2013 | May 31 | Sep 19 | May 24 | Sep 26 |
| 2012 | no data | Aug 28 | no data | Oct 17 |
| 2011 | Jun 17 | no data | Jun 3 | no data |
| 2010 | Jun 20 | Aug 31 | May 29 | Sep 23 |
| 2009 | May 13 | Sep 7 | Apr 30 | Sep 30 |
| 2008 | Jun 11 | Sep 21 | May 12 | Oct 9 |
| 2007 | Jun 7 | Aug 18 | Jun 7 | Sep 24 |
| 2006 | Jun 20 | Sep 16 | May 29 | Sep 16 |
| 2005 | Jun 19 | no data | May 29 | no data |
| 2004 | Jun 8 | Sep 15 | May 12 | Sep 21 |
| 2003 | Jun 26 | Sep 19 | May 16 | Oct 10 |
| 2002 | Jun 15 | Aug 7 | May 24 | Sep 7 |
| 2001 | Jun 14 | Oct 9 | May 4 | Oct 9 |
| 2000 | Jun 11 | Aug 19 | May 31 | Sep 24 |
| 1999 | no data | Aug 31 | no data | Oct 7 |
| 1998 | Jun 27 | Oct 5 | May 30 | Oct 5 |
| 1997 | Jul 1 | Sep 15 | May 5 | Oct 5 |
| 1996 | May 31 | Aug 20 | May 20 | Sep 17 |
| 1995 | Jun 16 | Aug 12 | Jun 8 | Sep 30 |
| 1994 | Jun 18 | Sep 3 | Jun 16 | Sep 10 |
| 1993 | Jun 12 | Sep 14 | May 8 | Sep 23 |
| 1992 | Jun 16 | Sep 25 | Jun 14 | Oct 7 |
| 1991 | Jun 25 | Aug 28 | Jun 1 | Oct 21 |
| 1990 | Jun 13 | Sep 15 | May 18 | Sep 17 |
| 1989 | Jun 1 | Aug 30 | May 27 | Oct 4 |
| 1988 | Jun 8 | Sep 13 | Jun 8 | Oct 27 |
| 1987 | Jul 21 | Sep 15 | May 25 | Oct 13 |
| 1986 | Jun 19 | Sep 9 | May 22 | Sep 14 |
| 1985 | Jun 27 | Aug 1 | Jun 2 | Sep 12 |
| 1984 | no data | Sep 22 | no data | Sep 24 |
| 1983 | Jul 23 | Sep 2 | Jul 8 | Sep 10 |
| 1982 | Jun 9 | no data | Jun 7 | no data |
| 1980 | Jul 11 | no data | Jun 6 | no data |
| 1979 | Jul 8 | Aug 24 | Jun 18 | Oct 17 |
| 1978 | Jun 25 | no data | Jun 25 | no data |
| 1976 | no data | Aug 3 | no data | Aug 7 |
| 1975 | no data | Aug 1 | no data | Aug 7 |
| 1970 | Jun 30 | no data | May 23 | no data |
| 1969 | Jun 28 | Aug 6 | May 16 | Sep 21 |
| 1968 | no data | Aug 17 | no data | Aug 22 |
| 1967 | Jun 2 | Sep 12 | May 14 | Sep 14 |
| 1966 | Jul 16 | Aug 23 | Jul 15 | Aug 31 |
| 1965 | Jul 11 | Sep 5 | Jul 10 | Sep 10 |
| 1964 | Jul 4 | no data | May 23 | no data |
| 1963 | Jul 30 | Aug 1 | Jun 29 | Aug 25 |
| 1962 | Jun 26 | Aug 10 | Jun 5 | Sep 19 |
| 1961 | Jul 31 | Aug 26 | Jul 31 | Aug 26 |
| 1960 | Jul 15 | Aug 1 | May 26 | Aug 23 |
| 1959 | Jul 8 | Aug 2 | Jun 10 | Aug 21 |
| 1958 | Jun 5 | no data | May 13 | no data |
| 1957 | Jul 31 | Aug 3 | May 14 | Aug 11 |
| 1956 | Jul 6 | Aug 3 | Jun 6 | Oct 13 |
| 1955 | Jul 25 | Aug 23 | Jul 6 | Aug 26 |
| 1954 | Jun 18 | Aug 6 | Jun 7 | Aug 15 |
| 1953 | Jul 25 | Aug 1 | Jul 1 | Sep 23 |
| 1952 | Jul 1 | Aug 13 | Jun 16 | Aug 27 |
| 1951 | Jul 21 | Aug 4 | Jul 6 | Sep 24 |
"none" means the station recorded no freeze at that threshold in that half of the year. "no data" means more than 10% of the season's daily readings were missing. Years with no usable data are left out. See the methodology for the rules, and the ZIP lookup for 1991–2020 frost probabilities.