San Marcos, California Weather
Coastal fog thickens at dawn. Day 76 of spring. Read this microseason across nine climate regions →
San Marcos weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 3Foggy——76°60°—
- ThursdayJun 4Foggy——77°58°+1°
- FridayJun 5Foggy——77°54°0°
- SaturdayJun 6Overcast——72°55°-5°
- SundayJun 7Overcast——72°53°0°
- MondayJun 8Overcast——73°53°+1°
- TuesdayJun 9Overcast——78°52°+5°
Ozone at AQI 95 now. AQI flat over the last 6 hours (within ±3 points). With UV 9.8 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 124 by mid-afternoon.
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 95 now. With UV 9.8 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 124 by mid-afternoon.
- Present
- AQI 95
- UV peak
- 9.8 at 1 PM
- Sky at peak
- clear
- Projected peak
- AQI 124
PM × Wind × Precip
PM2.5/PM10 ratio 0.69 with 10 mph wind — characteristic of long-range haze transport rather than a local source.
- PM2.5/PM10
- 0.69
- Wind
- breezy
- Recent rain
- 0h in last 6h
- Pattern
- transport
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
- 5:20 AM
- Moonset
- 3:14 PM
- In sign
- ♑︎ Capricorn
Coastal fog thickens at dawn
San Marcos at a glance
- Today vs. normal: 9°F below the seasonal normal for this latitude
- Last frost: March 6 (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
San Marcos's warmest month is August (~70°F mean) and its coldest is December (~53°F). Rainfall peaks in February (2.9 inches) and bottoms out in August (0.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 54° | 2.4″ | 3 |
| February | 54° | 2.9″ | 5 |
| March | 56° | 1.7″ | 3 |
| April | 58° | 0.9″ | 2 |
| May | 62° | 0.3″ | 1 |
| June | 66° | 0.1″ | 0 |
| July | 69° | 0.1″ | 0 |
| August | 70° | 0.0″ | 0 |
| September | 69° | 0.1″ | 0 |
| October | 64° | 0.6″ | 1 |
| November | 57° | 0.8″ | 2 |
| December | 53° | 2.0″ | 3 |
Regional context
San Marcos sits within a hot-summer Mediterranean climate region — a group of nearby cities that share comparable temperature ranges, seasonal rhythms, and growing conditions.
Similar climates: Los Angeles, CA, San Francisco, CA, San Diego, CA, Riverside, CA, Sacramento, CA.
Naturalist notes
By late spring, western fence lizards are emerging from winter dormancy on sun-warmed retaining walls and rock edges throughout the San Marcos area.
In the longer evenings of May, the constellation Scorpius begins climbing above the southeastern horizon after dusk, its brightest star Antares glowing a steady orange.
Frequently asked
- When does it freeze in San Marcos?
- San Marcos's last spring frost typically falls around mid-March, and the first fall frost arrives around mid-December.
- What is the rainy season in San Marcos?
- February is the wettest month with about 2.9 inches of rain on average; the city receives roughly 12 inches annually.
- What is the warmest month in San Marcos?
- August is typically warmest, averaging about 70°F.
- What is the coldest month in San Marcos?
- December is typically coldest, averaging about 53°F.
- When can I start a vegetable garden in San Marcos?
- 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 San Marcos get?
- San Marcos averages about 20 rainy days per year.
- What hardiness zone is San Marcos?
- San Marcos'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
San Marcos, California falls within a hot-summer Mediterranean climate zone. January temperatures hover near 54°F, while July averages 69°F — a 16°F seasonal swing.
Over the course of a year, San Marcos collects about 12 inches of precipitation, scattered across roughly 20 rainy days.
Latitude (33.1°N), nearby bodies of water, and local elevation set the tempo of the year here. Together they shape what can grow, when frost is most likely, and what the day-to-day weather narrative looks like.