Half Moon Bay, California climate: Normal weather by month, frost dates and records
Half Moon Bay's normal year runs from 43°F December nights to 66°F August afternoons, with 26.0 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.7°C, December lows of 6°C, August highs of 19°C, 661 mm of precipitation a year.
- NOAA stationHalf Moon Bay
- Station IDUSC00043714
- Location37.47°N 122.44°W
- Elevation27 ft (8 m)
- Population11,324
On October 23, the normal high in Half Moon Bay is 66°F and the normal low 47°F, and the chance of measurable rain or snow is 28%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Half Moon Bay.
- Jan 59° 43°
- Feb 60° 43°
- Mar 60° 44°
- Apr 61° 45°
- May 62° 48°
- Jun 64° 50°
- Jul 65° 53°
- Aug 66° 54°
- Sep 66° 51°
- Oct 66° 48°
- Nov 63° 45°
- Dec 59° 43°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Half Moon Bay each month?
August is the warmest month, with normal highs of 66°F; December the coldest, with normal lows of 43°F. The most precipitation falls in December (5.17 in), the least in July (0.14 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 59°F | 43°F | 51.4°F | 5.07 | 14 | <1 | 1 | 9 h 50 min |
| February | 60°F | 43°F | 51.3°F | 4.73 | 14 | <1 | 1 | 10 h 50 min |
| March | 60°F | 44°F | 52.1°F | 3.67 | 14 | <1 | <1 | 11 h 50 min |
| April | 61°F | 45°F | 52.9°F | 1.81 | 9 | <1 | <1 | 13 h 10 min |
| May | 62°F | 48°F | 54.9°F | 0.96 | 7 | <1 | <1 | 14 h 10 min |
| June | 64°F | 50°F | 56.9°F | 0.36 | 5 | <1 | <1 | 14 h 40 min |
| July | 65°F | 53°F | 58.8°F | 0.14 | 7 | <1 | <1 | 14 h 30 min |
| August | 66°F | 54°F | 59.7°F | 0.23 | 8 | <1 | <1 | 13 h 40 min |
| September | 66°F | 51°F | 58.8°F | 0.21 | 6 | <1 | <1 | 12 h 30 min |
| October | 66°F | 48°F | 57.1°F | 1.26 | 8 | <1 | <1 | 11 h 20 min |
| November | 63°F | 45°F | 53.7°F | 2.43 | 11 | <1 | 1 | 10 h 10 min |
| December | 59°F | 43°F | 50.9°F | 5.17 | 13 | <1 | 1 | 9 h 40 min |
| Year (annual) | 63°F | 47°F | 54.9°F | 26.04 | 116 | 1 | 5 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 15°C | 6°C | 10.8°C | 129 mm |
| February | 15°C | 6°C | 10.7°C | 120 mm |
| March | 16°C | 7°C | 11.2°C | 93 mm |
| April | 16°C | 7°C | 11.6°C | 46 mm |
| May | 17°C | 9°C | 12.7°C | 24 mm |
| June | 18°C | 10°C | 13.8°C | 9 mm |
| July | 18°C | 12°C | 14.9°C | 4 mm |
| August | 19°C | 12°C | 15.4°C | 6 mm |
| September | 19°C | 11°C | 14.9°C | 5 mm |
| October | 19°C | 9°C | 13.9°C | 32 mm |
| November | 17°C | 7°C | 12.1°C | 62 mm |
| December | 15°C | 6°C | 10.5°C | 131 mm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00043714; 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.
When is the best weather to visit Half Moon Bay?
Normal highs sit between 65°F and 85°F in August, September and October. Of those, September has the fewest days with rain (6).
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 USC00043714.
When is the last frost in Half Moon Bay?
In Half Moon Bay, the last spring frost (32°F) comes after February 6 in half of years and after March 25 in one year in ten; the first autumn frost comes before December 17 in half of years and before November 25 in one year in ten. A night at 32°F or colder comes at all in 82% of years here (NOAA).
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- February 61 year in 10 after March 25; 9 in 10 after December 17
- First autumn frost, half of years before
- December 171 year in 10 before November 25; 9 in 10 before February 13
NOAA puts the median frost-free season at 328 days, and the season without a hard freeze (28°F) at 365 days.
A hard freeze (28°F) comes after January 5 in half of springs and before December 31 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Half Moon Bay in zone 10a in ZIP code 94019. By the map's own method, the average of each year's coldest night over 1991-2020, Half Moon Bay's NOAA station is in zone 10a: the coldest night of a typical year reaches 31°F (25 complete years).
Frost dates for every NOAA station in California · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00043714; 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 in Half Moon Bay?
In a normal year in Half Moon Bay, 1 day a year reaches 90°F, 5 nights fall to 32°F or colder and 116 days bring measurable precipitation.
- Days at 90°F or more
- 1a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 5a normal year
- Days that stay below freezing
- fewer than 1high of 32°F or less
- Days with 0.01 inch of precipitation
- 116a normal year
The highest temperature in this station's record (since 1939) is 94°F, on October 27, 2003; the lowest is 19°F, on December 23, 1990.
The wettest calendar year on that record is 1996, with 36.27 in.
Source: NOAA NCEI 1991-2020 annual normals, station USC00043714; records: ACIS (NOAA Regional Climate Centers), station USC00043714. Records use complete months only; a month missing more than three days is left out.
How sunny is Half Moon Bay?
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Half Moon Bay, 4.7 kWh per square metre a day. June is the sunniest month (84%) and December the cloudiest (74%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 76% | 2.5 |
| February | 77% | 3.4 |
| March | 79% | 4.6 |
| April | 82% | 6.0 |
| May | 81% | 6.7 |
| June | 84% | 7.3 |
| July | 78% | 6.5 |
| August | 77% | 5.8 |
| September | 82% | 5.1 |
| October | 83% | 4.0 |
| November | 81% | 2.8 |
| December | 74% | 2.1 |
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 much heating and cooling does Half Moon Bay need?
A normal year in Half Moon Bay brings 3,701 heating degree days, 31% fewer than the median U.S. place (5,373), and 12 cooling degree days, 99% 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 1,952 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 422 | 0 |
| February | 385 | 0 |
| March | 402 | 0 |
| April | 365 | 0 |
| May | 315 | 0 |
| June | 244 | 1 |
| July | 194 | 1 |
| August | 165 | 2 |
| September | 187 | 3 |
| October | 249 | 5 |
| November | 340 | 1 |
| December | 436 | 0 |
| Year (annual) | 3,701 | 12 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00043714. 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.
Has Half Moon Bay been warmer than normal lately?
2025 averaged 55.8°F, 0.9°F above the 1991-2020 normal of 54.9°F. 1 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 54.5°F | −0.4°F | 25.49 |
| 2022 | 53.8°F | −1.1°F | 17.74 |
| 2023 | 54.3°F | −0.6°F | 31.46 |
| 2024 | 54.5°F | −0.4°F | 30.26 |
| 2025 | 55.8°F | +0.9°F | 19.50 |
Over 54 complete years from 1942 to 2025, the station's annual mean temperature rose at a fitted 3.2°F per century (+0.18°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00043714; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Half Moon Bay's climate compare?
Half Moon Bay is warmer than 41 of the other 218 places with their own NOAA record in California, and wetter than 161. 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, Half Moon Bay is Csb: temperate, dry-summer, warm 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.
Which places near Half Moon Bay share this climate record?
3 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- El Granada, CA5,231 people · 3 mi N
- Moss Beach, CA3,016 people · 4 mi NW
- Highlands, CA2,535 people · 6 mi NE
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Half Moon Bay's climate
What is the coldest month in Half Moon Bay?
December, with a normal high of 59°F and a normal low of 43°F. The warmest is August (66°F by day, 54°F at night).
Does it snow in Half Moon Bay?
Rarely: NOAA's normal is no measurable snow a year.
What is the rainiest month in Half Moon Bay?
December, with 5.17 in of precipitation in a normal year; the driest is July with 0.14 in.
What plant hardiness zone is Half Moon Bay in?
The USDA's 2023 map puts Half Moon Bay in zone 10a in ZIP code 94019. By the same method at Half Moon Bay's NOAA station, the coldest night of a typical year reaches 31°F (25 years, 1991-2020): zone 10a.
How late can frost come in Half Moon Bay?
In half of years the last 32°F night comes after February 6; in one year in ten it comes after March 25. Waiting until March 25 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Half Moon Bay in OctoberThis month day by day, its records and recent years
- California climateThe statewide normals and every place in the state
- Pacifica, CA8 miles from this station, 57.4°F a year
- Woodside, CA11 miles from this station, 60.1°F a year
- Redwood City, CA11 miles from this station, 59.4°F a year
- San Gregorio (2 mi SE), CA12 miles from this station, 54.8°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made