Weather in Union City, California
Fog and sun in daily rhythm. Day 58 of spring. Read this microseason across nine climate regions →
- TodayMay 16Partly Cloudy—70°50°
- SundayMay 17Overcast—76°48°
- MondayMay 18Partly Cloudy—83°57°
- TuesdayMay 19Clear—88°57°
- WednesdayMay 20Overcast—85°60°
- ThursdayMay 21Overcast—82°57°
- FridayMay 22Partly Cloudy—79°58°
- PM 2.5
- 6.4 μg/m³
- PM 10
- 9.5 μg/m³
- NO₂
- 1.8 μg/m³
- Ozone
- 95.0 μg/m³
- UV Index
- 4.1 Moderate
Flowers blooming in late autumn, a sure sign of a bad winter coming.
- Moonrise
- 12:25 PM
- Moonset
- 2:29 AM
- In sign
- ♉︎ Taurus
Fog and sun in daily rhythm
Union City at a glance
- Today vs. normal: 10°F below the seasonal normal for this latitude
- Last frost: April 2 (climatological average for this latitude)
- Microseason: 28 of 72, May 16–20
- Planting window: Direct sow okra, melons, and southern peas. Thin carrot rows.
Right now in the garden
Warm-season window is open
As of May 16, the last spring frost has passed for most years. Transplant tomatoes, peppers, eggplants, basil, and cucurbits (cucumbers, squash, melons) now. Direct-sow beans and corn into warm soil.
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.