Mount Hamilton, California climate: Climate normals at a NOAA weather station
Mount Hamilton's normal year runs from 38°F February nights to 79°F July afternoons, with 27.3 inches of precipitation and 18 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.8°C, February lows of 3°C, July highs of 26°C, 694 mm of precipitation a year.
- NOAA stationMount Hamilton
- Station IDUSC00045933
- Location37.34°N 121.64°W
- Elevation4,206 ft (1,282 m)
On October 23, the normal high in Mount Hamilton is 63°F and the normal low 51°F, and the chance of measurable rain or snow is 17%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Mount Hamilton.
- Jan 50° 39°
- Feb 49° 38°
- Mar 51° 39°
- Apr 55° 41°
- May 62° 47°
- Jun 71° 56°
- Jul 79° 65°
- Aug 79° 65°
- Sep 75° 60°
- Oct 66° 52°
- Nov 55° 43°
- Dec 49° 38°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at Mount Hamilton each month?
July is the warmest month, with normal highs of 79°F; February the coldest, with normal lows of 38°F. The most precipitation falls in January (5.03 in), the least in July (0.00 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 50°F | 39°F | 44.4°F | 5.03 | 4.2 | 12 | <1 | 8 | 9 h 50 min |
| February | 49°F | 38°F | 43.2°F | 4.79 | 5.3 | 12 | <1 | 8 | 10 h 50 min |
| March | 51°F | 39°F | 45.1°F | 4.42 | 3.8 | 11 | <1 | 8 | 11 h 50 min |
| April | 55°F | 41°F | 48.0°F | 2.22 | 1.8 | 8 | <1 | 7 | 13 h 10 min |
| May | 62°F | 47°F | 54.9°F | 1.30 | 0.0 | 6 | <1 | 2 | 14 h 10 min |
| June | 71°F | 56°F | 63.5°F | 0.28 | 0.0 | 2 | <1 | <1 | 14 h 40 min |
| July | 79°F | 65°F | 71.9°F | 0.00 | 0.0 | <1 | 1 | <1 | 14 h 30 min |
| August | 79°F | 65°F | 71.5°F | 0.05 | 0.0 | 1 | 1 | <1 | 13 h 40 min |
| September | 75°F | 60°F | 67.4°F | 0.17 | 0.0 | 2 | <1 | <1 | 12 h 30 min |
| October | 66°F | 52°F | 58.9°F | 1.34 | 0.0 | 4 | <1 | <1 | 11 h 20 min |
| November | 55°F | 43°F | 49.1°F | 2.99 | 0.9 | 9 | <1 | 4 | 10 h 10 min |
| December | 49°F | 38°F | 43.3°F | 4.72 | 2.1 | 12 | <1 | 9 | 9 h 40 min |
| Year (annual) | 62°F | 49°F | 55.1°F | 27.31 | 18.1 | 78 | 3 | 45 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 10°C | 4°C | 6.9°C | 128 mm | 11 cm |
| February | 9°C | 3°C | 6.2°C | 122 mm | 13 cm |
| March | 11°C | 4°C | 7.3°C | 112 mm | 10 cm |
| April | 13°C | 5°C | 8.9°C | 56 mm | 5 cm |
| May | 17°C | 9°C | 12.7°C | 33 mm | 0 cm |
| June | 22°C | 13°C | 17.5°C | 7 mm | 0 cm |
| July | 26°C | 18°C | 22.2°C | 0 mm | 0 cm |
| August | 26°C | 18°C | 21.9°C | 1 mm | 0 cm |
| September | 24°C | 16°C | 19.7°C | 4 mm | 0 cm |
| October | 19°C | 11°C | 14.9°C | 34 mm | 0 cm |
| November | 13°C | 6°C | 9.5°C | 76 mm | 2 cm |
| December | 9°C | 3°C | 6.3°C | 120 mm | 5 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00045933; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
Which months are mildest at Mount Hamilton?
Normal highs sit between 65°F and 85°F in June, July, August, September and October. Of those, July has the fewest days with rain (0).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00045933.
When is the last frost at Mount Hamilton?
In Mount Hamilton, the last spring frost (32°F) comes after May 3 in half of years and after June 5 in one year in ten; the first autumn frost comes before November 18 in half of years and before October 22 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- May 31 year in 10 after June 5; 9 in 10 after April 7
- First autumn frost, half of years before
- November 181 year in 10 before October 22; 9 in 10 before December 12
NOAA puts the median frost-free season at 197 days, and the season without a hard freeze (28°F) at 241 days.
A hard freeze (28°F) comes after April 10 in half of springs and before December 7 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Mount Hamilton in zone 9b in ZIP code 95140, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, the station is in zone 9a: the coldest night of a typical year reaches 22°F (30 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in California · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00045933; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get at Mount Hamilton?
In a normal year in Mount Hamilton, 3 days a year reach 90°F, 45 nights fall to 32°F or colder and 78 days bring measurable precipitation.
- Days at 90°F or more
- 3a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 45a normal year
- Days that stay below freezing
- 3high of 32°F or less
- Days with 0.01 inch of precipitation
- 78a normal year
- Days with 1 inch of snow or more
- 7a normal year
The highest temperature in this station's record (since 1948) is 103°F, on August 5, 1978; the lowest is 7°F, on December 21, 1990.
The wettest calendar year on that record is 1998, with 45.38 in; the snowiest season is 1981–82, with 49.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00045933; records: ACIS (NOAA Regional Climate Centers), station USC00045933. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Mount Hamilton?
Over a year 89% of the sunlight that would reach the ground under clear skies gets through the clouds at Mount Hamilton, 5.3 kWh per square metre a day. July is the sunniest month (97%) and January the cloudiest (74%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 74% | 2.4 |
| February | 78% | 3.5 |
| March | 81% | 4.8 |
| April | 85% | 6.2 |
| May | 90% | 7.5 |
| June | 95% | 8.3 |
| July | 97% | 8.2 |
| August | 97% | 7.4 |
| September | 95% | 6.0 |
| October | 91% | 4.4 |
| November | 83% | 2.9 |
| December | 74% | 2.2 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How many heating and cooling degree days does Mount Hamilton record?
A normal year at Mount Hamilton brings 4,386 heating degree days, 18% fewer than the median U.S. place (5,373), and 797 cooling degree days, 12% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,173 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 640 | 0 |
| February | 609 | 0 |
| March | 619 | 0 |
| April | 514 | 3 |
| May | 342 | 27 |
| June | 142 | 97 |
| July | 22 | 236 |
| August | 21 | 224 |
| September | 83 | 154 |
| October | 239 | 51 |
| November | 484 | 5 |
| December | 673 | 0 |
| Year (annual) | 4,386 | 797 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00045933. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Have recent years at Mount Hamilton been warmer than normal?
2025 averaged 55.9°F, 0.8°F above the 1991-2020 normal of 55.1°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 56.1°F | +1.0°F | 31.30 | – |
| 2022 | 56.3°F | +1.2°F | 24.38 | – |
| 2023 | 53.4°F | −1.7°F | 37.42 | – |
| 2024 | 56.2°F | +1.1°F | 34.97 | – |
| 2025 | 55.9°F | +0.8°F | 26.98 | – |
Over 52 complete years from 1954 to 2025, the station's annual mean temperature rose at a fitted 3.4°F per century (+0.19°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00045933; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Mount Hamilton's climate compare?
Mount Hamilton is warmer than 43 of the 219 places with their own NOAA record in California, and wetter than 163. Across the 7,247 U.S. stations with normals, its annual mean of 55.1°F is warmer than 61%.
In the Köppen classification computed from these normals, Mount Hamilton is Csa: temperate, dry-summer, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Questions about Mount Hamilton's climate
What is the coldest month at Mount Hamilton?
February, with a normal high of 49°F and a normal low of 38°F. The warmest is July (79°F by day, 65°F at night).
Does it snow at Mount Hamilton?
Yes: 18 inches in a normal year, falling on 11 days with 0.1 inch or more, the most in February (5.3 inches).
What is the rainiest month at Mount Hamilton?
January, with 5.03 in of precipitation in a normal year; the driest is July with 0.00 in.
What plant hardiness zone is Mount Hamilton in?
The USDA's 2023 map puts Mount Hamilton in zone 9b in ZIP code 95140, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches 22°F (30 years, 1991-2020): zone 9a.
How late can frost come at Mount Hamilton?
In half of years the last 32°F night comes after May 3; in one year in ten it comes after June 5. Waiting until June 5 leaves about a one-in-ten chance of a later frost.
Nearby and next
- California climateThe statewide normals and every place in the state
- San Jose, CA16 miles from this station, 60.7°F a year
- Los Gatos, CA19 miles from this station, 59.7°F a year
- Sunnyvale, CA23 miles from this station, 59.9°F a year
- Gilroy, CA24 miles from this station, 60.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made