Altadena, California Weather
Coastal fog thickens at dawn. Day 76 of spring. Read this microseason across nine climate regions →
Altadena weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 3Foggy——84°55°—
- ThursdayJun 4Foggy——86°55°+2°
- FridayJun 5Foggy——85°57°-1°
- SaturdayJun 6Overcast——79°63°-6°
- SundayJun 7Clear——77°60°-2°
- MondayJun 8Overcast——80°59°+3°
- TuesdayJun 9Partly Cloudy——82°63°+2°
PM2.5 at 25.0 µg/m³ (AQI 81) with a 0.69 fine-to-coarse ratio and 3 mph wind — combustion smoke trapped in calm air, not road dust. AQI flat over the last 6 hours (within ±3 points).
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 47 now. With UV 9.5 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 59 by mid-afternoon.
- Present
- AQI 47
- UV peak
- 9.5 at 1 PM
- Sky at peak
- clear
- Projected peak
- AQI 59
PM × Wind × Precip
PM2.5 at 25.0 µg/m³ (AQI 81) with a 0.69 fine-to-coarse ratio and 3 mph wind — combustion smoke trapped in calm air, not road dust.
- PM2.5/PM10
- 0.69
- 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).
The higher the clouds, the finer the weather.
- Moonrise
- 5:27 AM
- Moonset
- 3:15 PM
- In sign
- ♑︎ Capricorn
Coastal fog thickens at dawn
Altadena at a glance
- Today vs. normal: 14°F below the seasonal normal for this latitude
- Last frost: March 12 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Peak growing season
As of June 3, the growing season is at its peak — frost is months away. Continue succession-planting beans and summer squash. Start fall brassicas (broccoli, cabbage, kale) from seed indoors for transplanting in late summer.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | lettuce, peas, spinach, radishes | — |
| April | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | — |
| May | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | — | tomatoes, beans, summer squash |
| August | — | tomatoes, beans, summer squash |
| September | — | tomatoes, beans, summer squash |
| October | fall brassicas, garlic (overwinter), carrots | winter squash, tomatoes (last) |
| November | fall brassicas, garlic (overwinter), carrots | — |
| December | — | — |
A year in weather
Altadena's warmest month is August (~76°F mean) and its coldest is December (~55°F). Rainfall peaks in February (4.5 inches) and bottoms out in August (0.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 56° | 3.6″ | 5 |
| February | 56° | 4.5″ | 5 |
| March | 59° | 2.8″ | 4 |
| April | 62° | 0.9″ | 2 |
| May | 65° | 0.4″ | 1 |
| June | 69° | 0.1″ | 0 |
| July | 74° | 0.0″ | 0 |
| August | 76° | 0.0″ | 0 |
| September | 74° | 0.1″ | 0 |
| October | 68° | 0.7″ | 1 |
| November | 60° | 0.8″ | 2 |
| December | 55° | 2.5″ | 4 |
Regional context
Altadena sits within a hot-summer Mediterranean climate region — a cohort that shares similar temperature ranges, seasonal patterns, and growing conditions across nearby cities.
Similar climates: Los Angeles, CA, San Francisco, CA, San Diego, CA, Riverside, CA, Sacramento, CA.
Frequently asked
- When does it freeze in Altadena?
- Altadena's last spring frost typically falls around mid-March, and the first fall frost arrives around mid-December.
- What is the rainy season in Altadena?
- February is the wettest month with about 4.5 inches of rain on average; the city receives roughly 17 inches annually.
- What is the warmest month in Altadena?
- August is typically warmest, averaging about 76°F.
- What is the coldest month in Altadena?
- December is typically coldest, averaging about 55°F.
- When can I start a vegetable garden in Altadena?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-March); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does Altadena get?
- Altadena averages about 24 rainy days per year.
- What hardiness zone is Altadena?
- Altadena's USDA hardiness zone is determined by its lowest average winter temperature; check the USDA's online lookup with the city ZIP for the current zone designation.
Climate
Altadena, California sits in a hot-summer Mediterranean climate zone. January means hover near 56°F while July averages 74°F — a 18°F seasonal swing.
Across the year, Altadena receives about 17 inches of precipitation spread over roughly 24 rainy days.
The rhythm of the year is set by latitude (34.2°N), proximity to large water bodies, and elevation — all of which shape what grows here, when frost is likely, and what the weather story looks like day to day.