Hetch Hetchy, California climate: Climate normals at a NOAA weather station
Hetch Hetchy's normal year runs from 33°F December nights to 86°F July afternoons, with 36.9 inches of precipitation and 51 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.7°C, December lows of 0°C, July highs of 30°C, 937 mm of precipitation a year.
- NOAA stationHetch Hetchy
- Station IDUSC00043939
- Location37.96°N 119.78°W
- Elevation3,870 ft (1,180 m)
On October 23, the normal high in Hetch Hetchy is 67°F and the normal low 43°F, and the chance of measurable rain or snow is 16%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Hetch Hetchy.
- Jan 48° 32°
- Feb 52° 33°
- Mar 57° 36°
- Apr 62° 39°
- May 69° 46°
- Jun 78° 53°
- Jul 86° 59°
- Aug 86° 59°
- Sep 81° 54°
- Oct 70° 45°
- Nov 57° 37°
- Dec 47° 33°
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 Hetch Hetchy each month?
July is the warmest month, with normal highs of 86°F; December the coldest, with normal lows of 33°F. The most precipitation falls in January (6.30 in), the least in August (0.10 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 48°F | 32°F | 40.3°F | 6.30 | 9.7 | 11 | <1 | 17 | 9 h 50 min |
| February | 52°F | 33°F | 42.6°F | 5.70 | 13.5 | 10 | <1 | 13 | 10 h 50 min |
| March | 57°F | 36°F | 46.3°F | 5.71 | 10.8 | 11 | <1 | 10 | 11 h 50 min |
| April | 62°F | 39°F | 50.6°F | 3.51 | 4.3 | 8 | <1 | 5 | 13 h 10 min |
| May | 69°F | 46°F | 57.5°F | 2.36 | 0.1 | 6 | <1 | 1 | 14 h 10 min |
| June | 78°F | 53°F | 65.7°F | 0.62 | 0.0 | 2 | 2 | <1 | 14 h 50 min |
| July | 86°F | 59°F | 72.5°F | 0.35 | 0.0 | 1 | 9 | <1 | 14 h 30 min |
| August | 86°F | 59°F | 72.2°F | 0.10 | 0.0 | 1 | 8 | <1 | 13 h 40 min |
| September | 81°F | 54°F | 67.4°F | 0.37 | 0.0 | 2 | 3 | <1 | 12 h 30 min |
| October | 70°F | 45°F | 57.6°F | 2.15 | 0.0 | 4 | <1 | 1 | 11 h 20 min |
| November | 57°F | 37°F | 46.7°F | 3.80 | 3.0 | 7 | <1 | 7 | 10 h 10 min |
| December | 47°F | 33°F | 39.8°F | 5.91 | 10.0 | 10 | <1 | 17 | 9 h 30 min |
| Year (annual) | 66°F | 44°F | 54.9°F | 36.88 | 51.4 | 74 | 22 | 71 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 9°C | 0°C | 4.6°C | 160 mm | 25 cm |
| February | 11°C | 1°C | 5.9°C | 145 mm | 34 cm |
| March | 14°C | 2°C | 7.9°C | 145 mm | 27 cm |
| April | 17°C | 4°C | 10.3°C | 89 mm | 11 cm |
| May | 21°C | 8°C | 14.2°C | 60 mm | 0 cm |
| June | 26°C | 12°C | 18.7°C | 16 mm | 0 cm |
| July | 30°C | 15°C | 22.5°C | 9 mm | 0 cm |
| August | 30°C | 15°C | 22.3°C | 3 mm | 0 cm |
| September | 27°C | 12°C | 19.7°C | 9 mm | 0 cm |
| October | 21°C | 7°C | 14.2°C | 55 mm | 0 cm |
| November | 14°C | 3°C | 8.2°C | 97 mm | 8 cm |
| December | 8°C | 0°C | 4.3°C | 150 mm | 25 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00043939; 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 Hetch Hetchy?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, September has the fewest days with rain (2).
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 USC00043939.
When is the last frost at Hetch Hetchy?
In Hetch Hetchy, the last spring frost (32°F) comes after April 16 in half of years and after May 12 in one year in ten; the first autumn frost comes before November 12 in half of years and before October 24 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
- April 161 year in 10 after May 12; 9 in 10 after March 24
- First autumn frost, half of years before
- November 121 year in 10 before October 24; 9 in 10 before December 1
NOAA puts the median frost-free season at 208 days, and the season without a hard freeze (28°F) at 249 days.
A hard freeze (28°F) comes after March 25 in half of springs and before November 28 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Hetch Hetchy in zone 6a in ZIP code 95321, 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 8b: the coldest night of a typical year reaches 18°F (26 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 USC00043939; 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 Hetch Hetchy?
In a normal year in Hetch Hetchy, 22 days a year reach 90°F, 71 nights fall to 32°F or colder and 74 days bring measurable precipitation.
- Days at 90°F or more
- 22a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 71a normal year
- Days that stay below freezing
- 1high of 32°F or less
- Days with 0.01 inch of precipitation
- 74a normal year
- Days with 1 inch of snow or more
- 13a normal year
The highest temperature in this station's record (since 1910) is 106°F, on September 3, 1917; the lowest is −3°F, on January 3, 1912.
The wettest calendar year on that record is 1983, with 75.68 in; the snowiest season is 1936–37, with 193.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00043939; records: ACIS (NOAA Regional Climate Centers), station USC00043939. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Hetch Hetchy?
Over a year 86% of the sunlight that would reach the ground under clear skies gets through the clouds at Hetch Hetchy, 5.3 kWh per square metre a day. August is the sunniest month (96%) and December the cloudiest (73%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 75% | 2.6 |
| February | 73% | 3.4 |
| March | 75% | 4.7 |
| April | 78% | 6.0 |
| May | 84% | 7.2 |
| June | 93% | 8.4 |
| July | 94% | 8.2 |
| August | 96% | 7.5 |
| September | 94% | 6.1 |
| October | 89% | 4.5 |
| November | 81% | 3.0 |
| December | 73% | 2.3 |
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 Hetch Hetchy record?
A normal year at Hetch Hetchy brings 4,377 heating degree days, 19% fewer than the median U.S. place (5,373), and 729 cooling degree days, 20% fewer than the median (908). Six months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,125 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 767 | 0 |
| February | 626 | 0 |
| March | 580 | 0 |
| April | 431 | 1 |
| May | 255 | 23 |
| June | 77 | 97 |
| July | 5 | 238 |
| August | 7 | 229 |
| September | 50 | 122 |
| October | 248 | 21 |
| November | 549 | 0 |
| December | 781 | 0 |
| Year (annual) | 4,377 | 729 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00043939. 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 Hetch Hetchy been warmer than normal?
2024 averaged 56.5°F, 1.6°F above the 1991-2020 normal of 54.9°F. 3 of the 4 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 57.0°F | +2.1°F | 31.90 | 75.0 |
| 2022 | 56.1°F | +1.2°F | 26.47 | 32.0 |
| 2023 | 54.5°F | −0.4°F | 50.97 | 97.0 |
| 2024 | 56.5°F | +1.6°F | 34.99 | 39.0 |
Over 78 complete years from 1911 to 2024, the station's annual mean temperature rose at a fitted 1.5°F per century (+0.09°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00043939; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Hetch Hetchy's climate compare?
Hetch Hetchy is warmer than 41 of the 219 places with their own NOAA record in California, and wetter than 179. Across the 7,247 U.S. stations with normals, its annual mean of 54.9°F is warmer than 60%.
In the Köppen classification computed from these normals, Hetch Hetchy 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 Hetch Hetchy's climate
What is the coldest month at Hetch Hetchy?
December, with a normal high of 47°F and a normal low of 33°F. The warmest is July (86°F by day, 59°F at night).
Does it snow at Hetch Hetchy?
Yes: 51 inches in a normal year, falling on 14 days with 0.1 inch or more, the most in February (13.5 inches).
What is the rainiest month at Hetch Hetchy?
January, with 6.30 in of precipitation in a normal year; the driest is August with 0.10 in.
What plant hardiness zone is Hetch Hetchy in?
The USDA's 2023 map puts Hetch Hetchy in zone 6a in ZIP code 95321, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches 18°F (26 years, 1991-2020): zone 8b.
How late can frost come at Hetch Hetchy?
In half of years the last 32°F night comes after April 16; in one year in ten it comes after May 12. Waiting until May 12 leaves about a one-in-ten chance of a later frost.
Nearby and next
- California climateThe statewide normals and every place in the state
- Cherry Valley Dam, CA7 miles from this station, 54.6°F a year
- Yosemite Village (12 mi W), CA14 miles from this station, 49.5°F a year
- Yosemite Park Headquarters, CA18 miles from this station, 54.0°F a year
- Tuolumne Meadows Ranger Station, CA25 miles from this station, 38.4°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made