Mt Hamilton Weather Records (USC00045933)
Record envelope, standing records and threshold days for Mt Hamilton (USC00045933), California, United States, with 79 years of record.
Key Facts for Mt Hamilton
- Mt Hamilton (USC00045933) is a weather station in California, United States at 37.34 latitude and -121.63 longitude, 1,286 m (4,220 ft) above sea level.
- The station reports from 1948 to 2026, 79 years of record.
- 1,464 records set at Mt Hamilton still stand.
- Records are tracked for tmax, tmin, prcp, snow, snwd: an element needs 30 years of data to be eligible.
- Mt Hamilton tied a daily record high maximum temperature of 27.8 C (82.0 F) on 9 October 2026 (provisional).
Provisional Records
Records set in the last 60 days are provisional until they clear the revision window.
About the Station
- Location: California, United States, 37.34 latitude, -121.63 longitude.
- Elevation: 1,286 m (4,220 ft).
- Period of record: 1948 to 2026, 79 years.
- Eligible elements: tmax, tmin, prcp, snow, snwd.
Daily Record Envelope and 2026
17 days at or beyond a record| Month | Highest record high | Lowest record low | 2026 highest maximum | 2026 lowest minimum |
|---|---|---|---|---|
| Jan | 23.3 C (73.9 F) | -12.2 C (10.0 F) | 22.8 C (73.0 F) | -2.2 C (28.0 F) |
| Feb | 22.8 C (73.0 F) | -11.1 C (12.0 F) | 21.7 C (71.1 F) | -3.9 C (25.0 F) |
| Mar | 27.2 C (81.0 F) | -8.3 C (17.1 F) | 27.2 C (81.0 F) | 1.7 C (35.1 F) |
| Apr | 28.9 C (84.0 F) | -7.2 C (19.0 F) | 21.1 C (70.0 F) | -0.6 C (30.9 F) |
| May | 32.8 C (91.0 F) | -3.9 C (25.0 F) | 27.2 C (81.0 F) | 2.2 C (36.0 F) |
| Jun | 34.4 C (93.9 F) | -2.2 C (28.0 F) | 28.9 C (84.0 F) | 6.7 C (44.1 F) |
| Jul | 37.8 C (100.0 F) | 1.1 C (34.0 F) | 28.9 C (84.0 F) | 14.4 C (57.9 F) |
| Aug | 39.4 C (102.9 F) | 3.3 C (37.9 F) | 33.3 C (91.9 F) | 9.4 C (48.9 F) |
| Sep | 37.2 C (99.0 F) | 1.7 C (35.1 F) | 30.0 C (86.0 F) | 5.6 C (42.1 F) |
| Oct | 33.9 C (93.0 F) | -6.7 C (19.9 F) | 31.1 C (88.0 F) | 18.3 C (64.9 F) |
| Nov | 27.2 C (81.0 F) | -7.8 C (18.0 F) | n/a | n/a |
| Dec | 24.4 C (75.9 F) | -13.9 C (7.0 F) | n/a | n/a |
Which Years Hold Standing Records
1,464 standing records| Year set | Standing records |
|---|---|
| 1948 | 15 |
| 1949 | 43 |
| 1950 | 28 |
| 1951 | 16 |
| 1952 | 26 |
| 1953 | 48 |
| 1954 | 25 |
| 1955 | 43 |
| 1956 | 24 |
| 1957 | 18 |
| 1958 | 18 |
| 1959 | 14 |
| 1960 | 21 |
| 1961 | 22 |
| 1962 | 23 |
| 1963 | 12 |
| 1964 | 18 |
| 1965 | 17 |
| 1966 | 14 |
| 1967 | 24 |
| 1968 | 11 |
| 1969 | 8 |
| 1970 | 11 |
| 1971 | 38 |
| 1972 | 33 |
| 1973 | 12 |
| 1974 | 14 |
| 1975 | 17 |
| 1976 | 22 |
| 1977 | 14 |
| 1978 | 16 |
| 1979 | 6 |
| 1980 | 25 |
| 1981 | 8 |
| 1982 | 14 |
| 1983 | 14 |
| 1984 | 13 |
| 1985 | 27 |
| 1986 | 17 |
| 1987 | 24 |
| 1988 | 17 |
| 1989 | 21 |
| 1990 | 21 |
| 1991 | 16 |
| 1992 | 11 |
| 1993 | 4 |
| 1994 | 15 |
| 1995 | 23 |
| 1996 | 19 |
| 1997 | 7 |
| 1998 | 9 |
| 1999 | 12 |
| 2000 | 18 |
| 2001 | 14 |
| 2002 | 12 |
| 2003 | 17 |
| 2004 | 17 |
| 2005 | 12 |
| 2006 | 18 |
| 2007 | 13 |
| 2008 | 22 |
| 2009 | 22 |
| 2010 | 25 |
| 2011 | 23 |
| 2012 | 18 |
| 2013 | 12 |
| 2014 | 11 |
| 2015 | 19 |
| 2016 | 16 |
| 2017 | 30 |
| 2018 | 7 |
| 2019 | 23 |
| 2020 | 17 |
| 2021 | 13 |
| 2022 | 19 |
| 2023 | 15 |
| 2024 | 24 |
| 2025 | 15 |
| 2026 | 24 |
All-Time Record Progression
6 new records| Date | Kind | Detail |
|---|---|---|
| 1990-12-21 | Record low maximum temperature | Record low maximum temperature -7.8 C (18.0 F) |
| 1990-12-21 | Record low minimum temperature | Record low minimum temperature -13.9 C (7.0 F) |
| 1996-08-11 | Record high minimum temperature | Record high minimum temperature 28.3 C (82.9 F) |
| 2006-07-23 | Record high minimum temperature | Record high minimum temperature 28.9 C (84.0 F) |
| 2020-09-06 | Record high minimum temperature | Record high minimum temperature 29.4 C (84.9 F) |
| 2023-03-01 | Record snow depth | Record snow depth 63.5 cm (25.0 in) |
Wettest Day of Each Month
Dec: 174.5 mm (6.9 in)| Month | Record daily precipitation (mm) | Date |
|---|---|---|
| Jan | 70.9 mm (2.8 in) | 4 January 2008 |
| Feb | 76.2 mm (3.0 in) | 13 February 2025 |
| Mar | 64.3 mm (2.5 in) | 14 March 1952 |
| Apr | 47.5 mm (1.9 in) | 9 April 1965 |
| May | 48.8 mm (1.9 in) | 16 May 1996 |
| Jun | 18.5 mm (0.7 in) | 8 June 2000 |
| Jul | 12.7 mm (0.5 in) | 2 July 1980 |
| Aug | 19.1 mm (0.8 in) | 18 August 1975 |
| Sep | 29.5 mm (1.2 in) | 18 September 2022 |
| Oct | 139.7 mm (5.5 in) | 25 October 2021 |
| Nov | 148.6 mm (5.9 in) | 18 November 1950 |
| Dec | 174.5 mm (6.9 in) | 23 December 1955 |
Period of Record Coverage
1948 to 2026| Year | Days with data | Share of year | Complete |
|---|---|---|---|
| 1948 | 163 | 45% | No |
| 1949 | 279 | 76% | No |
| 1950 | 270 | 74% | No |
| 1951 | 330 | 90% | Yes |
| 1952 | 364 | 99% | Yes |
| 1953 | 363 | 99% | Yes |
| 1954 | 364 | 100% | Yes |
| 1955 | 356 | 98% | Yes |
| 1956 | 359 | 98% | Yes |
| 1957 | 365 | 100% | Yes |
| 1958 | 333 | 91% | Yes |
| 1959 | 296 | 81% | No |
| 1960 | 309 | 84% | No |
| 1961 | 308 | 84% | No |
| 1962 | 309 | 85% | No |
| 1963 | 329 | 90% | Yes |
| 1964 | 328 | 90% | No |
| 1965 | 306 | 84% | No |
| 1966 | 288 | 79% | No |
| 1967 | 312 | 85% | No |
| 1968 | 348 | 95% | Yes |
| 1969 | 329 | 90% | Yes |
| 1970 | 359 | 98% | Yes |
| 1971 | 358 | 98% | Yes |
| 1972 | 352 | 96% | Yes |
| 1973 | 353 | 97% | Yes |
| 1974 | 314 | 86% | No |
| 1975 | 363 | 99% | Yes |
| 1976 | 363 | 99% | Yes |
| 1977 | 364 | 100% | Yes |
| 1978 | 364 | 100% | Yes |
| 1979 | 363 | 99% | Yes |
| 1980 | 364 | 99% | Yes |
| 1981 | 365 | 100% | Yes |
| 1982 | 356 | 98% | Yes |
| 1983 | 364 | 100% | Yes |
| 1984 | 354 | 97% | Yes |
| 1985 | 301 | 82% | No |
| 1986 | 365 | 100% | Yes |
| 1987 | 355 | 97% | Yes |
| 1988 | 358 | 98% | Yes |
| 1989 | 356 | 98% | Yes |
| 1990 | 363 | 99% | Yes |
| 1991 | 360 | 99% | Yes |
| 1992 | 365 | 100% | Yes |
| 1993 | 359 | 98% | Yes |
| 1994 | 359 | 98% | Yes |
| 1995 | 362 | 99% | Yes |
| 1996 | 364 | 99% | Yes |
| 1997 | 363 | 99% | Yes |
| 1998 | 360 | 99% | Yes |
| 1999 | 360 | 99% | Yes |
| 2000 | 363 | 99% | Yes |
| 2001 | 362 | 99% | Yes |
| 2002 | 364 | 100% | Yes |
| 2003 | 362 | 99% | Yes |
| 2004 | 364 | 99% | Yes |
| 2005 | 357 | 98% | Yes |
| 2006 | 360 | 99% | Yes |
| 2007 | 363 | 99% | Yes |
| 2008 | 363 | 99% | Yes |
| 2009 | 360 | 99% | Yes |
| 2010 | 361 | 99% | Yes |
| 2011 | 344 | 94% | Yes |
| 2012 | 361 | 99% | Yes |
| 2013 | 359 | 98% | Yes |
| 2014 | 365 | 100% | Yes |
| 2015 | 363 | 99% | Yes |
| 2016 | 366 | 100% | Yes |
| 2017 | 362 | 99% | Yes |
| 2018 | 364 | 100% | Yes |
| 2019 | 365 | 100% | Yes |
| 2020 | 366 | 100% | Yes |
| 2021 | 365 | 100% | Yes |
| 2022 | 365 | 100% | Yes |
| 2023 | 365 | 100% | Yes |
| 2024 | 366 | 100% | Yes |
| 2025 | 363 | 99% | Yes |
| 2026 | 281 | 77% | No |
Latest Records
20| Date | Station | Record | Value | Beat old record by | Old record stood | Significance |
|---|---|---|---|---|---|---|
| 9 October 2026 | Mt Hamilton, US | daily high max (Tie, Provisional) | 27.8 C (82.0 F) | tie | 29 years | 3 of 100 (Routine) |
| 5 October 2026 | Mt Hamilton, US | daily high min (Tie, Provisional) | 23.9 C (75.0 F) | tie | 39 years | 4 of 100 (Routine) |
| 4 October 2026 | Mt Hamilton, US | daily high min (Provisional) | 23.9 C (75.0 F) | 0.6 C (1.1 F) | 45 years | 21 of 100 (Routine) |
| 3 October 2026 | Mt Hamilton, US | daily high min (Tie, Provisional) | 24.4 C (75.9 F) | tie | 1 year | 1 of 100 (Routine) |
| 13 June 2026 | Mt Hamilton, US | daily high min | 22.8 C (73.0 F) | 0.6 C (1.1 F) | 40 years | 20 of 100 (Routine) |
| 12 June 2026 | Mt Hamilton, US | daily high min | 22.8 C (73.0 F) | 1.1 C (2.0 F) | 40 years | 20 of 100 (Routine) |
| 28 May 2026 | Mt Hamilton, US | daily low max | 7.2 C (45.0 F) | 0.6 C (1.1 F) | 28 years | 16 of 100 (Routine) |
| 11 May 2026 | Mt Hamilton, US | daily high max | 27.2 C (81.0 F) | 1.6 C (2.9 F) | 67 years | 29 of 100 (Routine) |
| 12 April 2026 | Mt Hamilton, US | daily rain | 40.9 mm (1.6 in) | 6.9 mm (0.27 in) | 16 years | 19 of 100 (Routine) |
| 29 March 2026 | Mt Hamilton, US | daily high min | 15.0 C (59.0 F) | 1.1 C (2.0 F) | 21 years | 15 of 100 (Routine) |
| 28 March 2026 | Mt Hamilton, US | daily high min (Tie) | 13.3 C (55.9 F) | tie | 56 years | 6 of 100 (Routine) |
| 27 March 2026 | Mt Hamilton, US | daily high min | 15.0 C (59.0 F) | 1.1 C (2.0 F) | 40 years | 21 of 100 (Routine) |
| 27 March 2026 | Mt Hamilton, US | daily high max | 22.8 C (73.0 F) | 0.6 C (1.1 F) | 11 years | 11 of 100 (Routine) |
| 24 March 2026 | Mt Hamilton, US | daily high min | 15.6 C (60.1 F) | 1.2 C (2.2 F) | 4 years | 10 of 100 (Routine) |
| 23 March 2026 | Mt Hamilton, US | daily high max | 21.1 C (70.0 F) | 1.1 C (2.0 F) | 4 years | 10 of 100 (Routine) |
| 23 March 2026 | Mt Hamilton, US | daily high min (Tie) | 13.9 C (57.0 F) | tie | 4 years | 2 of 100 (Routine) |
| 22 March 2026 | Mt Hamilton, US | daily high min | 15.0 C (59.0 F) | 3.9 C (7.0 F) | 65 years | 34 of 100 (Routine) |
| 22 March 2026 | Mt Hamilton, US | daily high max (Tie) | 21.7 C (71.1 F) | tie | 21 years | 3 of 100 (Routine) |
| 21 March 2026 | Mt Hamilton, US | daily high max | 23.3 C (73.9 F) | 1.6 C (2.9 F) | 21 years | 16 of 100 (Routine) |
| 20 March 2026 | Mt Hamilton, US | monthly high max | 27.2 C (81.0 F) | 0.5 C (0.9 F) | 0 years | 17 of 100 (Routine) |
Climate Trend
63 complete years, 1952 to 2025| Year | Annual mean temperature | Difference from the station mean |
|---|---|---|
| 1952 | 11.0 C | -1.61 C |
| 1954 | 11.9 C | -0.75 C |
| 1955 | 10.7 C | -1.90 C |
| 1956 | 11.7 C | -0.93 C |
| 1957 | 11.5 C | -1.17 C |
| 1960 | 12.6 C | -0.02 C |
| 1964 | 11.3 C | -1.30 C |
| 1967 | 12.6 C | +0.00 C |
| 1968 | 12.9 C | +0.25 C |
| 1970 | 12.8 C | +0.19 C |
| 1971 | 11.7 C | -0.98 C |
| 1972 | 12.5 C | -0.14 C |
| 1973 | 12.1 C | -0.58 C |
| 1975 | 11.9 C | -0.76 C |
| 1976 | 13.0 C | +0.32 C |
| 1977 | 12.8 C | +0.21 C |
| 1978 | 12.7 C | +0.05 C |
| 1979 | 12.6 C | -0.08 C |
| 1980 | 13.0 C | +0.37 C |
| 1981 | 13.3 C | +0.66 C |
| 1982 | 11.4 C | -1.21 C |
| 1983 | 11.7 C | -0.92 C |
| 1984 | 13.0 C | +0.32 C |
| 1986 | 13.0 C | +0.32 C |
| 1987 | 12.3 C | -0.37 C |
| 1988 | 14.0 C | +1.41 C |
| 1989 | 13.9 C | +1.25 C |
| 1990 | 12.3 C | -0.30 C |
| 1991 | 12.8 C | +0.16 C |
| 1992 | 13.2 C | +0.53 C |
| 1993 | 12.0 C | -0.64 C |
| 1994 | 12.2 C | -0.46 C |
| 1995 | 12.7 C | +0.05 C |
| 1996 | 13.2 C | +0.60 C |
| 1997 | 12.5 C | -0.13 C |
| 1998 | 10.7 C | -1.91 C |
| 1999 | 12.3 C | -0.29 C |
| 2000 | 12.5 C | -0.15 C |
| 2001 | 13.0 C | +0.35 C |
| 2002 | 12.9 C | +0.27 C |
| 2003 | 13.0 C | +0.34 C |
| 2004 | 12.6 C | -0.04 C |
| 2005 | 12.6 C | +0.01 C |
| 2006 | 12.6 C | +0.01 C |
| 2007 | 12.6 C | -0.05 C |
| 2008 | 13.1 C | +0.45 C |
| 2009 | 12.7 C | +0.04 C |
| 2010 | 11.8 C | -0.86 C |
| 2011 | 11.8 C | -0.84 C |
| 2012 | 13.0 C | +0.35 C |
| 2013 | 13.4 C | +0.76 C |
| 2014 | 14.3 C | +1.63 C |
| 2015 | 14.0 C | +1.32 C |
| 2016 | 13.4 C | +0.80 C |
| 2017 | 13.7 C | +1.03 C |
| 2018 | 13.7 C | +1.06 C |
| 2019 | 12.3 C | -0.34 C |
| 2020 | 13.9 C | +1.25 C |
| 2021 | 13.4 C | +0.75 C |
| 2022 | 13.5 C | +0.89 C |
| 2023 | 11.9 C | -0.77 C |
| 2024 | 13.4 C | +0.79 C |
| 2025 | 13.3 C | +0.64 C |
The annual mean temperature here has risen by 0.2 C (0.1 to 0.3) per decade over 1952 to 2025. In Fahrenheit: 0.4 F (0.2 to 0.5) per decade. The slope is a straight line fitted to 63 complete years; the brackets give its 95 percent interval.
| Measure | Per decade (C) | Per decade (F) | Period | Complete years | Reading |
|---|---|---|---|---|---|
| Annual mean temperature | 0.2 C (0.1 to 0.3) per decade | 0.4 F (0.2 to 0.5) per decade | 1952 to 2025 | 63 | Rise |
| Mean daily maximum | 0.07 C (-0.03 to 0.16) per decade | 0.1 F (-0.1 to 0.3) per decade | 1952 to 2025 | 63 | Not clearly different from zero |
| Mean daily minimum | 0.3 C (0.3 to 0.4) per decade | 0.6 F (0.5 to 0.8) per decade | 1952 to 2025 | 63 | Rise |
A year is complete when all 12 months have at least 20 days of both daily maximum and daily minimum readings. The annual mean is the mean of the monthly means. The trend describes this one station over this period; it does not say what caused the change.
Extremes by Year
1948 to 2026| Measure | Record | Year of the record | Median year | Years with a value |
|---|---|---|---|---|
| Hottest day (TXx) | 39.4 C (102.9 F) | 1978 | 33.3 C (91.9 F) | 79 |
| Coldest night (TNn) | -13.9 C (7.0 F) | 1990 | -6.1 C (21.0 F) | 79 |
| Wettest day (Rx1day) | 174.5 mm (6.9 in) | 1955 | 47.5 mm (1.9 in) | 79 |
| Wettest five days (Rx5day) | 345.1 mm (13.6 in) | 1955 | 99.6 mm (3.9 in) | 79 |
| Longest dry spell (CDD) | 179 days | 1987 | 113 days | 79 |
Hottest day (TXx)
| Year | Hottest day (TXx) |
|---|---|
| 1948 | 33.3 C (91.9 F) |
| 1949 | 32.8 C (91.0 F) |
| 1950 | 34.4 C (93.9 F) |
| 1951 | 33.3 C (91.9 F) |
| 1952 | 32.8 C (91.0 F) |
| 1953 | 32.8 C (91.0 F) |
| 1954 | 32.8 C (91.0 F) |
| 1955 | 36.1 C (97.0 F) |
| 1956 | 32.8 C (91.0 F) |
| 1957 | 34.4 C (93.9 F) |
| 1958 | 32.2 C (90.0 F) |
| 1959 | 35.0 C (95.0 F) |
| 1960 | 35.0 C (95.0 F) |
| 1961 | 35.0 C (95.0 F) |
| 1962 | 31.7 C (89.1 F) |
| 1963 | 32.2 C (90.0 F) |
| 1964 | 31.7 C (89.1 F) |
| 1965 | 30.6 C (87.1 F) |
| 1966 | 32.2 C (90.0 F) |
| 1967 | 33.9 C (93.0 F) |
| 1968 | 32.8 C (91.0 F) |
| 1969 | 34.4 C (93.9 F) |
| 1970 | 33.3 C (91.9 F) |
| 1971 | 36.7 C (98.1 F) |
| 1972 | 37.8 C (100.0 F) |
| 1973 | 32.8 C (91.0 F) |
| 1974 | 32.2 C (90.0 F) |
| 1975 | 35.0 C (95.0 F) |
| 1976 | 33.9 C (93.0 F) |
| 1977 | 34.4 C (93.9 F) |
| 1978 | 39.4 C (102.9 F) |
| 1979 | 33.3 C (91.9 F) |
| 1980 | 34.4 C (93.9 F) |
| 1981 | 37.8 C (100.0 F) |
| 1982 | 33.3 C (91.9 F) |
| 1983 | 32.2 C (90.0 F) |
| 1984 | 35.6 C (96.1 F) |
| 1985 | 29.4 C (84.9 F) |
| 1986 | 31.1 C (88.0 F) |
| 1987 | 32.8 C (91.0 F) |
| 1988 | 36.7 C (98.1 F) |
| 1989 | 32.2 C (90.0 F) |
| 1990 | 32.8 C (91.0 F) |
| 1991 | 32.8 C (91.0 F) |
| 1992 | 31.1 C (88.0 F) |
| 1993 | 32.8 C (91.0 F) |
| 1994 | 30.6 C (87.1 F) |
| 1995 | 31.7 C (89.1 F) |
| 1996 | 33.9 C (93.0 F) |
| 1997 | 33.3 C (91.9 F) |
| 1998 | 35.6 C (96.1 F) |
| 1999 | 33.3 C (91.9 F) |
| 2000 | 32.8 C (91.0 F) |
| 2001 | 33.3 C (91.9 F) |
| 2002 | 33.9 C (93.0 F) |
| 2003 | 32.2 C (90.0 F) |
| 2004 | 31.7 C (89.1 F) |
| 2005 | 32.8 C (91.0 F) |
| 2006 | 35.0 C (95.0 F) |
| 2007 | 33.3 C (91.9 F) |
| 2008 | 33.9 C (93.0 F) |
| 2009 | 32.8 C (91.0 F) |
| 2010 | 33.3 C (91.9 F) |
| 2011 | 29.4 C (84.9 F) |
| 2012 | 33.3 C (91.9 F) |
| 2013 | 33.3 C (91.9 F) |
| 2014 | 32.8 C (91.0 F) |
| 2015 | 32.8 C (91.0 F) |
| 2016 | 33.9 C (93.0 F) |
| 2017 | 36.1 C (97.0 F) |
| 2018 | 33.3 C (91.9 F) |
| 2019 | 31.7 C (89.1 F) |
| 2020 | 36.7 C (98.1 F) |
| 2021 | 35.0 C (95.0 F) |
| 2022 | 37.2 C (99.0 F) |
| 2023 | 34.4 C (93.9 F) |
| 2024 | 37.2 C (99.0 F) |
| 2025 | 31.7 C (89.1 F) |
| 2026 | 33.3 C (91.9 F) |
Coldest night (TNn)
| Year | Coldest night (TNn) |
|---|---|
| 1948 | -8.3 C (17.1 F) |
| 1949 | -12.2 C (10.0 F) |
| 1950 | -12.2 C (10.0 F) |
| 1951 | -8.3 C (17.1 F) |
| 1952 | -12.2 C (10.0 F) |
| 1953 | -8.3 C (17.1 F) |
| 1954 | -6.1 C (21.0 F) |
| 1955 | -7.2 C (19.0 F) |
| 1956 | -5.0 C (23.0 F) |
| 1957 | -8.9 C (16.0 F) |
| 1958 | -7.8 C (18.0 F) |
| 1959 | -5.6 C (21.9 F) |
| 1960 | -7.2 C (19.0 F) |
| 1961 | -4.4 C (24.1 F) |
| 1962 | -12.2 C (10.0 F) |
| 1963 | -7.8 C (18.0 F) |
| 1964 | -5.6 C (21.9 F) |
| 1965 | -8.3 C (17.1 F) |
| 1966 | -6.7 C (19.9 F) |
| 1967 | -11.1 C (12.0 F) |
| 1968 | -9.4 C (15.1 F) |
| 1969 | -8.3 C (17.1 F) |
| 1970 | -3.9 C (25.0 F) |
| 1971 | -7.8 C (18.0 F) |
| 1972 | -12.8 C (9.0 F) |
| 1973 | -6.7 C (19.9 F) |
| 1974 | -7.8 C (18.0 F) |
| 1975 | -7.8 C (18.0 F) |
| 1976 | -5.6 C (21.9 F) |
| 1977 | -5.6 C (21.9 F) |
| 1978 | -7.2 C (19.0 F) |
| 1979 | -6.1 C (21.0 F) |
| 1980 | -5.6 C (21.9 F) |
| 1981 | -3.3 C (26.1 F) |
| 1982 | -6.7 C (19.9 F) |
| 1983 | -3.9 C (25.0 F) |
| 1984 | -4.4 C (24.1 F) |
| 1985 | -5.6 C (21.9 F) |
| 1986 | -3.9 C (25.0 F) |
| 1987 | -7.8 C (18.0 F) |
| 1988 | -4.4 C (24.1 F) |
| 1989 | -8.3 C (17.1 F) |
| 1990 | -13.9 C (7.0 F) |
| 1991 | -5.0 C (23.0 F) |
| 1992 | -5.0 C (23.0 F) |
| 1993 | -6.1 C (21.0 F) |
| 1994 | -6.1 C (21.0 F) |
| 1995 | -5.0 C (23.0 F) |
| 1996 | -6.1 C (21.0 F) |
| 1997 | -10.0 C (14.0 F) |
| 1998 | -9.4 C (15.1 F) |
| 1999 | -5.6 C (21.9 F) |
| 2000 | -3.3 C (26.1 F) |
| 2001 | -6.1 C (21.0 F) |
| 2002 | -6.7 C (19.9 F) |
| 2003 | -5.0 C (23.0 F) |
| 2004 | -5.6 C (21.9 F) |
| 2005 | -3.3 C (26.1 F) |
| 2006 | -5.0 C (23.0 F) |
| 2007 | -7.8 C (18.0 F) |
| 2008 | -5.6 C (21.9 F) |
| 2009 | -7.2 C (19.0 F) |
| 2010 | -6.7 C (19.9 F) |
| 2011 | -7.8 C (18.0 F) |
| 2012 | -6.1 C (21.0 F) |
| 2013 | -6.7 C (19.9 F) |
| 2014 | -5.0 C (23.0 F) |
| 2015 | -3.3 C (26.1 F) |
| 2016 | -3.9 C (25.0 F) |
| 2017 | -3.3 C (26.1 F) |
| 2018 | -6.1 C (21.0 F) |
| 2019 | -5.6 C (21.9 F) |
| 2020 | -4.4 C (24.1 F) |
| 2021 | -5.0 C (23.0 F) |
| 2022 | -6.7 C (19.9 F) |
| 2023 | -5.6 C (21.9 F) |
| 2024 | -3.9 C (25.0 F) |
| 2025 | -3.3 C (26.1 F) |
| 2026 | -3.9 C (25.0 F) |
Wettest day (Rx1day)
| Year | Wettest day (Rx1day) |
|---|---|
| 1948 | 49.0 mm (1.9 in) |
| 1949 | 40.6 mm (1.6 in) |
| 1950 | 148.6 mm (5.9 in) |
| 1951 | 57.2 mm (2.3 in) |
| 1952 | 64.3 mm (2.5 in) |
| 1953 | 43.7 mm (1.7 in) |
| 1954 | 64.5 mm (2.5 in) |
| 1955 | 174.5 mm (6.9 in) |
| 1956 | 49.8 mm (2.0 in) |
| 1957 | 28.2 mm (1.1 in) |
| 1958 | 57.9 mm (2.3 in) |
| 1959 | 20.1 mm (0.8 in) |
| 1960 | 38.1 mm (1.5 in) |
| 1961 | 33.3 mm (1.3 in) |
| 1962 | 30.5 mm (1.2 in) |
| 1963 | 32.5 mm (1.3 in) |
| 1964 | 33.0 mm (1.3 in) |
| 1965 | 47.5 mm (1.9 in) |
| 1966 | 40.1 mm (1.6 in) |
| 1967 | 34.3 mm (1.4 in) |
| 1968 | 38.4 mm (1.5 in) |
| 1969 | 27.9 mm (1.1 in) |
| 1970 | 40.1 mm (1.6 in) |
| 1971 | 25.9 mm (1.0 in) |
| 1972 | 39.4 mm (1.6 in) |
| 1973 | 57.2 mm (2.3 in) |
| 1974 | 50.3 mm (2.0 in) |
| 1975 | 41.7 mm (1.6 in) |
| 1976 | 30.0 mm (1.2 in) |
| 1977 | 45.7 mm (1.8 in) |
| 1978 | 28.2 mm (1.1 in) |
| 1979 | 37.6 mm (1.5 in) |
| 1980 | 30.7 mm (1.2 in) |
| 1981 | 52.8 mm (2.1 in) |
| 1982 | 72.4 mm (2.9 in) |
| 1983 | 63.2 mm (2.5 in) |
| 1984 | 25.4 mm (1.0 in) |
| 1985 | 38.1 mm (1.5 in) |
| 1986 | 46.7 mm (1.8 in) |
| 1987 | 44.5 mm (1.8 in) |
| 1988 | 37.1 mm (1.5 in) |
| 1989 | 42.7 mm (1.7 in) |
| 1990 | 54.4 mm (2.1 in) |
| 1991 | 53.3 mm (2.1 in) |
| 1992 | 38.1 mm (1.5 in) |
| 1993 | 63.5 mm (2.5 in) |
| 1994 | 21.6 mm (0.9 in) |
| 1995 | 50.8 mm (2.0 in) |
| 1996 | 101.6 mm (4.0 in) |
| 1997 | 50.8 mm (2.0 in) |
| 1998 | 62.2 mm (2.4 in) |
| 1999 | 39.1 mm (1.5 in) |
| 2000 | 54.6 mm (2.1 in) |
| 2001 | 48.0 mm (1.9 in) |
| 2002 | 91.4 mm (3.6 in) |
| 2003 | 49.0 mm (1.9 in) |
| 2004 | 44.2 mm (1.7 in) |
| 2005 | 37.8 mm (1.5 in) |
| 2006 | 47.5 mm (1.9 in) |
| 2007 | 24.6 mm (1.0 in) |
| 2008 | 70.9 mm (2.8 in) |
| 2009 | 54.1 mm (2.1 in) |
| 2010 | 42.4 mm (1.7 in) |
| 2011 | 37.1 mm (1.5 in) |
| 2012 | 72.4 mm (2.9 in) |
| 2013 | 24.4 mm (1.0 in) |
| 2014 | 89.7 mm (3.5 in) |
| 2015 | 49.3 mm (1.9 in) |
| 2016 | 49.5 mm (1.9 in) |
| 2017 | 56.4 mm (2.2 in) |
| 2018 | 48.3 mm (1.9 in) |
| 2019 | 52.6 mm (2.1 in) |
| 2020 | 47.5 mm (1.9 in) |
| 2021 | 139.7 mm (5.5 in) |
| 2022 | 86.6 mm (3.4 in) |
| 2023 | 51.3 mm (2.0 in) |
| 2024 | 54.9 mm (2.2 in) |
| 2025 | 76.2 mm (3.0 in) |
| 2026 | 40.9 mm (1.6 in) |
Wettest five days (Rx5day)
| Year | Wettest five days (Rx5day) |
|---|---|
| 1948 | 72.6 mm (2.9 in) |
| 1949 | 69.9 mm (2.8 in) |
| 1950 | 244.3 mm (9.6 in) |
| 1951 | 117.4 mm (4.6 in) |
| 1952 | 168.4 mm (6.6 in) |
| 1953 | 68.2 mm (2.7 in) |
| 1954 | 121.6 mm (4.8 in) |
| 1955 | 345.1 mm (13.6 in) |
| 1956 | 75.5 mm (3.0 in) |
| 1957 | 78.5 mm (3.1 in) |
| 1958 | 112.9 mm (4.4 in) |
| 1959 | 43.3 mm (1.7 in) |
| 1960 | 97.1 mm (3.8 in) |
| 1961 | 47.6 mm (1.9 in) |
| 1962 | 78.1 mm (3.1 in) |
| 1963 | 69.6 mm (2.7 in) |
| 1964 | 87.0 mm (3.4 in) |
| 1965 | 112.0 mm (4.4 in) |
| 1966 | 52.5 mm (2.1 in) |
| 1967 | 80.3 mm (3.2 in) |
| 1968 | 52.9 mm (2.1 in) |
| 1969 | 78.0 mm (3.1 in) |
| 1970 | 97.2 mm (3.8 in) |
| 1971 | 42.2 mm (1.7 in) |
| 1972 | 80.7 mm (3.2 in) |
| 1973 | 110.3 mm (4.3 in) |
| 1974 | 73.2 mm (2.9 in) |
| 1975 | 80.3 mm (3.2 in) |
| 1976 | 70.7 mm (2.8 in) |
| 1977 | 61.9 mm (2.4 in) |
| 1978 | 80.0 mm (3.1 in) |
| 1979 | 74.4 mm (2.9 in) |
| 1980 | 123.4 mm (4.9 in) |
| 1981 | 101.8 mm (4.0 in) |
| 1982 | 123.0 mm (4.8 in) |
| 1983 | 125.2 mm (4.9 in) |
| 1984 | 69.9 mm (2.8 in) |
| 1985 | 73.7 mm (2.9 in) |
| 1986 | 141.4 mm (5.6 in) |
| 1987 | 68.4 mm (2.7 in) |
| 1988 | 74.4 mm (2.9 in) |
| 1989 | 64.1 mm (2.5 in) |
| 1990 | 78.5 mm (3.1 in) |
| 1991 | 96.3 mm (3.8 in) |
| 1992 | 99.6 mm (3.9 in) |
| 1993 | 133.8 mm (5.3 in) |
| 1994 | 52.1 mm (2.1 in) |
| 1995 | 143.0 mm (5.6 in) |
| 1996 | 126.5 mm (5.0 in) |
| 1997 | 129.3 mm (5.1 in) |
| 1998 | 136.3 mm (5.4 in) |
| 1999 | 103.5 mm (4.1 in) |
| 2000 | 133.9 mm (5.3 in) |
| 2001 | 101.3 mm (4.0 in) |
| 2002 | 139.9 mm (5.5 in) |
| 2003 | 63.9 mm (2.5 in) |
| 2004 | 122.8 mm (4.8 in) |
| 2005 | 107.3 mm (4.2 in) |
| 2006 | 93.0 mm (3.7 in) |
| 2007 | 70.9 mm (2.8 in) |
| 2008 | 110.8 mm (4.4 in) |
| 2009 | 102.4 mm (4.0 in) |
| 2010 | 91.5 mm (3.6 in) |
| 2011 | 108.2 mm (4.3 in) |
| 2012 | 153.5 mm (6.0 in) |
| 2013 | 25.4 mm (1.0 in) |
| 2014 | 110.3 mm (4.3 in) |
| 2015 | 118.1 mm (4.6 in) |
| 2016 | 110.9 mm (4.4 in) |
| 2017 | 194.3 mm (7.6 in) |
| 2018 | 84.8 mm (3.3 in) |
| 2019 | 118.3 mm (4.7 in) |
| 2020 | 108.2 mm (4.3 in) |
| 2021 | 171.2 mm (6.7 in) |
| 2022 | 197.1 mm (7.8 in) |
| 2023 | 161.3 mm (6.4 in) |
| 2024 | 111.2 mm (4.4 in) |
| 2025 | 122.4 mm (4.8 in) |
| 2026 | 62.3 mm (2.5 in) |
Longest dry spell (CDD)
| Year | Longest dry spell (CDD) |
|---|---|
| 1948 | 92 days |
| 1949 | 90 days |
| 1950 | 95 days |
| 1951 | 149 days |
| 1952 | 72 days |
| 1953 | 82 days |
| 1954 | 148 days |
| 1955 | 120 days |
| 1956 | 130 days |
| 1957 | 109 days |
| 1958 | 149 days |
| 1959 | 139 days |
| 1960 | 127 days |
| 1961 | 106 days |
| 1962 | 99 days |
| 1963 | 88 days |
| 1964 | 82 days |
| 1965 | 132 days |
| 1966 | 53 days |
| 1967 | 118 days |
| 1968 | 79 days |
| 1969 | 88 days |
| 1970 | 132 days |
| 1971 | 95 days |
| 1972 | 155 days |
| 1973 | 117 days |
| 1974 | 84 days |
| 1975 | 50 days |
| 1976 | 64 days |
| 1977 | 119 days |
| 1978 | 131 days |
| 1979 | 73 days |
| 1980 | 103 days |
| 1981 | 136 days |
| 1982 | 77 days |
| 1983 | 56 days |
| 1984 | 125 days |
| 1985 | 97 days |
| 1986 | 133 days |
| 1987 | 179 days |
| 1988 | 147 days |
| 1989 | 68 days |
| 1990 | 113 days |
| 1991 | 69 days |
| 1992 | 101 days |
| 1993 | 128 days |
| 1994 | 139 days |
| 1995 | 106 days |
| 1996 | 143 days |
| 1997 | 50 days |
| 1998 | 86 days |
| 1999 | 82 days |
| 2000 | 83 days |
| 2001 | 125 days |
| 2002 | 129 days |
| 2003 | 68 days |
| 2004 | 113 days |
| 2005 | 130 days |
| 2006 | 131 days |
| 2007 | 140 days |
| 2008 | 163 days |
| 2009 | 92 days |
| 2010 | 128 days |
| 2011 | 63 days |
| 2012 | 78 days |
| 2013 | 82 days |
| 2014 | 131 days |
| 2015 | 112 days |
| 2016 | 144 days |
| 2017 | 44 days |
| 2018 | 128 days |
| 2019 | 113 days |
| 2020 | 159 days |
| 2021 | 174 days |
| 2022 | 131 days |
| 2023 | 146 days |
| 2024 | 134 days |
| 2025 | 138 days |
| 2026 | 96 days |
Each chart shows one value per year; the dot marks the record year. TXx is the hottest daily maximum, TNn the coldest daily minimum, Rx1day and Rx5day the largest one-day and five-day rain totals, and CDD the longest run of days with less than 1 mm of rain. A year with missing days can understate an extreme.
Frost Dates and Growing Season
62 years with a frostAcross 62 years with a frost, the median last spring frost at Mt Hamilton falls on 11 May and the median first autumn frost on 17 November, which leaves a median of 188 days between them.
In 1995 to 2024 the median growing season was 202 days. That is 19 days more than in 1952 to 1992.
Fitted over all years, the growing season changes by +4.9 days per decade at this station.
| Measure | Median, all years | Earliest period (1952 to 1992) | Recent period (1995 to 2024) | Recent against earliest | Fitted trend |
|---|---|---|---|---|---|
| Last spring frost | 11 May | 15 May | 5 May | 10 days earlier | -2.8 days per decade |
| First autumn frost | 17 November | 13 November | 21 November | 8 days later | +2.1 days per decade |
| Growing days | 188 days | 183 days | 202 days | 19 days more | +4.9 days per decade |
A frost day is a day with a daily minimum at or below 0 C (32 F). The last spring frost and the first autumn frost are the last and first such days of the cold season, and growing days are the days between them. A negative trend for the last spring frost means it comes earlier.
Rainfall Return Levels
72 years, 1951 to 2025A day with at least 45.3 mm (1.8 in) of rain is expected about once in 2 years. A day with at least 139.9 mm (5.5 in) of rain is expected about once in 100 years.
| Expected about once in | A day with at least | Note |
|---|---|---|
| 2 years | 45.3 mm (1.8 in) | |
| 5 years | 64.2 mm (2.5 in) | |
| 10 years | 78.9 mm (3.1 in) | |
| 25 years | 100.5 mm (4.0 in) | |
| 50 years | 119.1 mm (4.7 in) | |
| 100 years | 139.9 mm (5.5 in) | Longer than the 72 years of record |
The levels come from a generalised extreme value (GEV) distribution fitted by L-moments to the wettest-day total of each year, 72 years of values from 1951 to 2025.
A return level is an estimate. It is least reliable for the long periods, 50 and 100 years, and for any period longer than the record behind the fit, where the fit has to reach past the largest day actually observed. It is not a forecast.
The largest wettest-day totals in the fit: 174.5 mm (6.9 in) in 1955; 139.7 mm (5.5 in) in 2021; 101.6 mm (4.0 in) in 1996.
Station Changes
2 suspected2 changes were suspected in the annual mean temperature of Mt Hamilton, at 1967 and 1990. Each is measured against neighbouring stations.
- Relative to 5 neighbouring stations, the station's annual mean temperature from 1967 ran 0.6 C (1.1 F) higher than in the years before (likely change).
- Relative to 5 neighbouring stations, the station's annual mean temperature from 1990 ran 0.6 C (1.1 F) lower than in the years before (likely change).
| Year | Shift (C) | Shift (F) | Strength | Neighbours |
|---|---|---|---|---|
| 1967 | +0.6 | +1.1 | likely | 5 |
| 1990 | -0.6 | -1.1 | likely | 5 |
Possible change at the station (a move, a new instrument or a new site); the record is kept as measured. A "likely" change has a larger test statistic than a "possible" one. Neither says why the station differs from its neighbours. How changes are found, and the largest ones.
Climate Twins
2011 to 2025 against 1961 to 1990Over 2011 to 2025, Mt Hamilton had a mean temperature of 13.3 C (55.9 F) and 707.5 mm (27.9 in) of rain a year. The 3 stations whose 1961 to 1990 climate was closest to that are Mt Wilson Cbs (United States, 472 km away), Palomar Mtn Obsy (United States, 619 km away) and Julian Wynola (United States, 654 km away).
| Twin station | Country | Distance away | Mean temperature, 1961-1990 | Rain a year, 1961-1990 | Climate difference |
|---|---|---|---|---|---|
| Mt Wilson Cbs | United States | 472 km (293 mi) | 13.2 C (55.8 F) | 873.4 mm (34.4 in) | 0.88 |
| Palomar Mtn Obsy | United States | 619 km (385 mi) | 13.2 C (55.7 F) | 608.0 mm (23.9 in) | 0.89 |
| Julian Wynola | United States | 654 km (406 mi) | 13.9 C (57.0 F) | 605.1 mm (23.8 in) | 1.08 |
Twins are stations, not cities. A twin is one of the three stations at least 100 km away whose earlier climate is closest to this station's recent one, so a close match does not mean the two places look alike in other ways. A station move or a gap in a record can change that station's averages. The list describes past climate; it is not a forecast and does not say what caused any change. How twins are found, and a search for any station.
Download the Data
Source: NOAA National Centers for Environmental Information, Global Historical Climatology Network Daily (GHCN-Daily). Records are computed by World Extreme Weather Monitor and are not official NOAA products. (US Government open data (NOAA NCEI)) Data as of 2026-10-12 (12 October 2026). Records are computed by this site and are not official.
Data as of . Last revised (2026-10-13).