Union City, California Weather
Coastal fog thickens at dawn. Day 77 of spring. Read this microseason across nine climate regions →
Union City weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 3Overcast——74°53°—
- ThursdayJun 4Overcast——77°53°+3°
- FridayJun 5Overcast——82°53°+5°
- SaturdayJun 6Overcast——72°56°-10°
- SundayJun 7Overcast——75°53°+3°
- MondayJun 8Light Drizzle—0.01″74°55°-1°
- TuesdayJun 9Overcast——69°56°-5°
PM2.5 at 7.2 µg/m³, PM10 at 10.2 µg/m³ — typical background levels with no transport signature. AQI flat over the last 6 hours (within ±4 points).
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion during the projected peak around 7 AM.
What's driving it
PM × Wind × Precip
PM2.5 at 7.2 µg/m³, PM10 at 10.2 µg/m³ — typical background levels with no transport signature.
- PM2.5/PM10
- 0.71
- Wind
- light
- Recent rain
- 0h in last 6h
- Pattern
- background
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).
A summer fog for fair, a winter fog for rain.
- Moonrise
- 6:33 AM
- Moonset
- 4:22 PM
- In sign
- ♑︎ Capricorn
Coastal fog thickens at dawn
Union City at a glance
- Today vs. normal: 18°F below the seasonal normal for this latitude
- Last frost: April 2 (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 4, 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 | — | — |
| April | lettuce, peas, spinach, radishes | — |
| May | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | tomatoes, peppers, beans, squash | tomatoes, beans, summer squash |
| August | — | tomatoes, beans, summer squash |
| September | fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| October | fall brassicas, garlic (overwinter), carrots | winter squash, tomatoes (last) |
| November | — | — |
| December | — | — |
A year in weather
Union City's warmest month is August (~68°F mean) and its coldest is December (~51°F). Rainfall peaks in February (3.2 inches) and bottoms out in July (0.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 51° | 3.0″ | 6 |
| February | 53° | 3.2″ | 7 |
| March | 56° | 2.5″ | 6 |
| April | 58° | 1.2″ | 4 |
| May | 62° | 0.5″ | 2 |
| June | 65° | 0.2″ | 0 |
| July | 67° | 0.0″ | 0 |
| August | 68° | 0.0″ | 0 |
| September | 67° | 0.1″ | 0 |
| October | 63° | 0.7″ | 2 |
| November | 55° | 1.6″ | 4 |
| December | 51° | 3.0″ | 7 |
Regional context
Union City 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 Union City?
- Union City's last spring frost typically falls around mid-April, and the first fall frost arrives around mid-November.
- What is the rainy season in Union City?
- February is the wettest month with about 3.2 inches of rain on average; the city receives roughly 16 inches annually.
- What is the warmest month in Union City?
- August is typically warmest, averaging about 68°F.
- What is the coldest month in Union City?
- December is typically coldest, averaging about 51°F.
- When can I start a vegetable garden in Union City?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-April); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does Union City get?
- Union City averages about 37 rainy days per year.
- What hardiness zone is Union City?
- Union City'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
Union City, California sits in a hot-summer Mediterranean climate zone. January means hover near 51°F while July averages 67°F — a 17°F seasonal swing.
Across the year, Union City receives about 16 inches of precipitation spread over roughly 37 rainy days.
The rhythm of the year is set by latitude (37.6°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.