Los Altos, California Weather
Ceanothus blooms again. Day 93 of summer. Read this microseason across nine climate regions →
Los Altos weather forecast — hour by hour, 7-day outlook, NOAA radar
Conditions updated 1:50 AM PDT · Open-Meteo
- TodaySep 21Clear later——75°56°—
- TuesdaySep 22Partly Cloudy——79°54°+4°
- WednesdaySep 23Overcast——93°56°+14°
- ThursdaySep 24Overcast——92°57°-1°
- FridaySep 25Overcast——85°57°-7°
- SaturdaySep 26Overcast——92°58°+7°
- SundaySep 27Overcast——88°53°-4°
Air quality now AQI 50 · Good
AQI 50 (Good), driven by PM2.5. AQI flat over the last 6 hours (within ±3 points). PM2.5 at 7.8 µg/m³ (AQI 43) with a 0.73 fine-to-coarse ratio and 3 mph wind — combustion smoke trapped in stagnant air, not road dust.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
PM × Wind × Precip
PM2.5 at 7.8 µg/m³ (AQI 43) with a 0.73 fine-to-coarse ratio and 3 mph wind — combustion smoke trapped in stagnant air, not road dust.
- PM2.5/PM10
- 0.73
- Wind
- calm
- Recent rain
- 0h in last 6h
- Pattern
- stagnant smoke
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
September dries up ditches or breaks down bridges.
- Moonrise
- 4:37 PM
- Moonset
- 1:43 AM
- In sign
- ♑︎ Capricorn
Ceanothus blooms again
Read this microseason across nine climate regions →
All 72 microseasons on the year wheel →
Los Altos at a glance
- Today vs. normal: Today averages 66°F (high 75°F, low 56°F), 2°F below the 68°F normal for Sep 21
- Last frost: January 6 (1991–2020 median, NOAA station 6 km away)
- Microseason: Sep 21–25
- Planting calendar: September — plant tomatoes, peppers, beans, squash; harvest tomatoes, peppers, beans, summer squash, winter squash
15-Day Forecast — Los Altos
- Mon75°56°1%
- Tue79°54°1%
- Wed93°56°0%
- Thu92°57°0%
- Fri85°57°0%
- Sat92°58°0%
- Sun88°53°1%
- Mon90°56°1%
- Tue97°66°1%
- Wed81°60°3%
- Thu87°57°1%
- Fri86°55°3%
- Sat75°53°6%
- Sun87°57°6%
- Mon89°64°6%
Forecast data from Open-Meteo (CC BY 4.0).
Right now in the garden
Peak growing season
As of September 21, the growing season is at its peak — the first frost (around December 23) is weeks away. Fall transplants go in about 10–12 weeks before the first frost, September 30 to October 14 here. This city's planting calendar for September: plant tomatoes, peppers, beans, and squash; harvest tomatoes, peppers, beans, summer squash, and winter squash.
Sun & seasons in Los Altos
Los Altos sits in Santa Clara County, where the year’s longest day runs 14h 44m of daylight and its shortest just 9h 35m — a swing of +5h 9m between the June and December solstices. Clocks spring forward on Sunday, March 8, 2026 and fall back on Sunday, November 1, 2026.
Los Angeles, the state’s largest city, lies about 306 miles to the SE. The nearest town Los Altos tracks is Sunnyvale, roughly 4 miles to the ENE.
Air quality in Los Altos
Air quality in Los Altos’s county has trended cleaner since 2020; its cleanest year on record was 2023 (median AQI 43).
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | lettuce, peas, spinach, radishes | lettuce, spinach, radishes, fall brassicas, carrots |
| February | — | lettuce, peas, spinach, radishes |
| March | — | lettuce, peas, spinach |
| April | tomatoes, peppers, beans, squash | peas |
| May | tomatoes, peppers, beans, squash | garlic |
| June | beans, squash | beans, summer squash |
| July | beans, squash | tomatoes, peppers, beans, summer squash |
| August | tomatoes, peppers, beans, squash | tomatoes, peppers, beans, summer squash, winter squash |
| September | tomatoes, peppers, beans, squash | tomatoes, peppers, beans, summer squash, winter squash |
| October | beans, squash, fall brassicas, carrots | tomatoes, peppers, beans, summer squash, winter squash |
| November | garlic (overwinter) | tomatoes, peppers, beans, summer squash, winter squash |
| December | lettuce, peas, spinach, radishes, garlic (overwinter) | tomatoes, peppers, beans, summer squash, winter squash, fall brassicas, carrots |
A year in weather
Los Altos's warmest month is August (~70°F mean) and its coldest is December (~51°F). Rainfall peaks in January (2.8 inches) and bottoms out in July (0.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 51° | 2.8″ | 9 |
| February | 53° | 2.7″ | 10 |
| March | 56° | 2.1″ | 9 |
| April | 59° | 1.1″ | 6 |
| May | 63° | 0.4″ | 3 |
| June | 67° | 0.2″ | 1 |
| July | 70° | 0.0″ | 0 |
| August | 70° | 0.1″ | 0 |
| September | 69° | 0.1″ | 1 |
| October | 64° | 0.5″ | 3 |
| November | 56° | 1.3″ | 7 |
| December | 51° | 2.3″ | 10 |
Regional context
Similar climates Loyola, CA, Los Altos Hills, CA, Mountain View, CA
Los Altos's climate, from NOAA NCEI 1991-2020 station normals, pairs 51°F Januarys with 70°F Julys — a 19°F swing. About 13.5 inches of precipitation falls over roughly 59 days a year.
Los Altos's moisture rides winter storm tracks: January brings 2.8 inches over 9.2 wet days, while July sees only 0.0 inches across 0.1 days in the dry warm season. That groups Los Altos with places like Loyola, CA, Los Altos Hills, CA and Mountain View, CA on the same cool-season storm track.
By January 6 the frosts ease in Los Altos, opening the season for lettuce, chard, arugula, and mustard greens. Warm-soil crops in Los Altos wait about two weeks past Los Altos's last frost, once the soil warms. Los Altos's window closes around December 23 as Los Altos's overnight lows return below freezing. In about half of years, Los Altos's last freeze comes after January 6.
Similar climates: Loyola, CA, Los Altos Hills, CA, Mountain View, CA, Palo Alto, CA, Sunnyvale, CA.
Frequently asked
- When does it freeze in Los Altos?
- Los Altos's last spring frost lands near January 6, and in Los Altos the first fall frost follows around December 23.
- What is the rainy season in Los Altos?
- Los Altos sees its heaviest rain in January (around 2.8 inches), part of roughly 13 inches a year.
- What is the warmest month in Los Altos?
- Los Altos peaks in August, when the mean runs near 70°F.
- What is the coldest month in Los Altos?
- December is Los Altos's coldest month, averaging about 51°F.
- When can I start a vegetable garden in Los Altos?
- Around January 6, start frost-hardy crops in Los Altos; tomatoes and basil belong a fortnight later.
- How many rainy days does Los Altos get?
- Los Altos averages about 59 days with measurable rain or snow each year.
- What hardiness zone is Los Altos?
- Since December in Los Altos averages 51°F, Los Altos's USDA zone follows that floor — confirm it by ZIP.
- What is the 10-day forecast for Los Altos?
- Los Altos's extended outlook — daily high and low temperatures and precipitation chances for each upcoming day — is in the daily forecast above.
- Will it rain this week in Los Altos?
- See this week's day-by-day rain chances for Los Altos in the daily forecast above, and the next 24 hours in the hourly chart.
- What is the weather like right now in Los Altos?
- Current conditions for Los Altos and the next 24 hours — temperature, precipitation chance, and wind by the hour — are in the hourly forecast chart above.
- How often is the Los Altos forecast updated?
- The Los Altos forecast on this page is built from Open-Meteo weather-model data and refreshes regularly through the day.
- When are sunrise and sunset in Los Altos?
- Today's sunrise and sunset times for Los Altos are in the Almanac section above, along with civil dawn, civil dusk, and day length. Day length is longest near the summer solstice and shortest near the winter solstice.
- How accurate is the weather forecast for Los Altos?
- The next few days in Los Altos's forecast are the most reliable; accuracy declines beyond about a week as weather-model uncertainty grows.
Los Altos sits at 37.4°N; its climate zone is hot-summer Mediterranean (Köppen approximation).
ZIP codes in Los Altos
- 94022
- 94023
- 94024