Union City Weather
Town • San Francisco Bay Area
Union City fills the gap between Hayward and Fremont, from the bay plain up to the first grassy hills of the East Bay ridge. It was incorporated in 1959 by joining Alvarado, Decoto, and New Haven, and Alvarado was Alameda County's original county seat. Alameda Creek crosses town on its way to the bay, and BART stops at Union Square. Dry Creek Pioneer Regional Park climbs the slopes behind the city from its May Road entrance.
Plan your week
10-Day Forecast
Hour by hour
Hourly Forecast
Current Conditions
Comfort Breakdown
Union City weather today and through the year
It's 53°F at Union City right now (feels like 50°F), with 6 mph wind and a comfort score of 77. Monday's forecast high at Union City is 56°F, 10°F below the mid November normal of 66°F. The best window today is 9 AM to noon, at about 55°F with a 4 mph wind (comfort 58).
August is the warmest month at Union City, with an average high of 81°F. December is the coldest, with an average low of 41°F. December is the wettest month (3.6 in.), out of about 18.3 in. a year. By typical temperature, wind, cloud, humidity, and rain odds, the most comfortable months at Union City are August, September, and June. The best hours are usually 11 AM to 2 PM in August, 11 AM to 2 PM in September, and 11 AM to 2 PM in June.
Union City sits between two openings in the East Bay hills that pull bay air inland on hot afternoons. One is the I-580 pass toward Dublin to the north, and the other is Niles Canyon just to the south. When the Livermore Valley heats up, the breeze crossing town is drawn toward both. Union City is often breezier and a touch cooler than the Mission San Jose side of Fremont.
Forecast updated November 15, 2026 at 4:00 AM PST. Climate figures come from NOAA 1991-2020 normals. Hourly patterns come from NOAA's HRRR hourly analysis from September 2014 to April 2026.
What to expect at Union City in the next few days
No active National Weather Service alerts for this location.
Best time to go
The best window today is 9 AM to noon, at about 55°F with a 4 mph wind (comfort 58).
Best day this week
Of the next 7 days, Friday looks best for Union City, with a 62°F high and midday comfort near 81. Thursday looks weakest (50).
Rain
Next good chance of rain: today (84%, about 0.26 in.).
Live weather map
Weather around Union City right now
Overcast and 53° at Union City right now.
About the live weather map for Union City
The map centers on Union City and stacks fog, satellite clouds, and precipitation radar on one view. Clouds come from the GOES-West satellite and rain from NOAA radar, and both show current conditions. Fog comes from our HRRR-based fog model, and the slider steps through its forecast for the next 12 hours.
Dots mark nearby places with their current temperature, colored by comfort score. Use the layer buttons to turn any layer off, or open the full map for every destination in the region.
Nearby Temperature Comparison
Conditions at nearby San Francisco Bay Area destinations
Tip: Bay Area temperatures can change by 20 to 30°F over a short distance because of microclimates.
Union City vs nearby places
Typical summer conditions compared with Union City, from the same NOAA HRRR hourly record. The list shows the closest places, then nearby places whose climate differs the most.
| Place | Distance | Summer afternoons | Morning fog | Afternoon wind | Compared with Union City |
|---|---|---|---|---|---|
| Garin Regional Park | 2.6 mi | -1°F | 43% | 10 mph | more summer morning fog (43% vs 18% of morning hours) and about 27% more rain a year |
| Coyote Hills Regional Park | 3.7 mi | -13°F | 21% | 14 mph | about 13°F cooler on summer afternoons and windier summer afternoons (14 vs 9 mph) |
| Fremont | 4.3 mi | +2°F | 17% | 9 mph | a very similar climate |
| Purisima Creek Redwoods | 20.7 mi | -12°F | 57% | 7 mph | more summer morning fog (57% vs 18% of morning hours) and about 84% more rain a year |
| Half Moon Bay | 22.9 mi | -12°F | 64% | 8 mph | more summer morning fog (64% vs 18% of morning hours) and about 12°F cooler on summer afternoons |
| Pacifica | 24.3 mi | -19°F | 56% | 9 mph | about 19°F cooler on summer afternoons and more summer morning fog (56% vs 18% of morning hours) |
Places with a climate like Union City's
- Sunnyvale (16 mi away): nearly the same temperatures every month
- Mountain View (15 mi away): nearly the same temperatures every month
- Los Altos Hills (16 mi away): nearly the same temperatures every month
Climate Dashboard
Current conditions vs. NOAA normals and recent destination baseline
What the Union City climate comparisons mean
These cards compare recent conditions at Union City with the available local baseline. Temperature and year-to-date rainfall use long-term normals when available. Fog, sunshine, wind, and comfort use the matching recent or modeled baseline identified on each card.
Positive and negative differences describe how Union City departs from its own usual pattern. They should not be read as a direct comparison with another city or as a forecast beyond the period shown.
Union City weather by month
August is the warmest month at Union City, with an average high of 81°F. December is the coldest, with an average low of 41°F. December is the wettest month (3.6 in.), out of about 18.3 in. a year. Morning fog peaks in July, when fog or low cloud covers 20% of the hours from 6 to 10 AM. August has the clearest middays, with clouds covering about 13% of the sky from 11 AM to 3 PM.
By typical temperature, wind, cloud, humidity, and rain odds, the most comfortable months at Union City are August, September, and June. The best hours are usually 11 AM to 2 PM in August, 11 AM to 2 PM in September, and 11 AM to 2 PM in June.
| Month | Avg high | Avg low | Rain | Rainy days | Morning fog | Midday cloud | Afternoon wind | Daylight | Comfort |
|---|---|---|---|---|---|---|---|---|---|
| Jan | 59°F | 41°F | 3.5 in | 8 | 13% | 32% | 5 mph | 9.9 h | 61 |
| Feb | 62°F | 43°F | 3.6 in | 8 | 9% | 26% | 7 mph | 10.7 h | 63 |
| Mar | 66°F | 45°F | 2.8 in | 7 | 9% | 31% | 8 mph | 11.9 h | 66 |
| Apr | 69°F | 47°F | 1.3 in | 5 | 9% | 25% | 9 mph | 13.2 h | 75 |
| May | 73°F | 50°F | 0.6 in | 3 | 9% | 23% | 10 mph | 14.2 h | 79 |
| Jun | 79°F | 54°F | 0.1 in | 2 | 15% | 14% | 10 mph | 14.8 h | 90 |
| Jul | 81°F | 56°F | 0.0 in | 0 | 20% | 13% | 9 mph | 14.5 h | 90 |
| Aug | 81°F | 56°F | 0.0 in | 1 | 19% | 13% | 9 mph | 13.6 h | 92 |
| Sep | 81°F | 55°F | 0.1 in | 1 | 13% | 15% | 8 mph | 12.3 h | 92 |
| Oct | 76°F | 51°F | 0.8 in | 4 | 9% | 17% | 7 mph | 11.1 h | 86 |
| Nov | 66°F | 45°F | 1.8 in | 6 | 10% | 21% | 5 mph | 10.1 h | 77 |
| Dec | 59°F | 41°F | 3.6 in | 8 | 15% | 33% | 5 mph | 9.6 h | 59 |
Morning fog is the share of hours from 6 to 10 AM with fog or low cloud. Midday cloud is the average from 11 AM to 3 PM, and afternoon wind is the average from 1 to 5 PM. The highlighted rows are the most comfortable months.
In summer, recent daily NOAA readings at Union City average about 5°F cooler than the 1991-2020 normals. The normals average over a wider area that also covers nearby terrain. Read the monthly highs as a rough range, and use the recent months below for what Union City has actually seen.
What makes Union City's weather different
When the fog burns off
11 AMwhen July fog usually thins (27% foggy at 8 AM)
Fog or low cloud covers Union City in 27% of 8 AM hours in July, the foggiest month. It usually thins to a third of that by 11 AM. April mornings are the least foggy (9%).
When the wind picks up
1 PMwhen afternoon wind builds, February–October
From February through October, wind at Union City typically builds after 1 PM. In May it peaks around 5 PM, averaging 11 mph with 3% of those hours windy, while mornings average 4 mph.
Microclimate
−13°FCoyote Hills Regional Park, 3.7 mi away, on summer afternoons
Coyote Hills Regional Park, 3.7 miles away, runs about 13°F cooler than Union City on summer afternoons.
Daylight
9.6–14.8 hof daylight, Dec to Jun
Days at Union City range from about 9.6 hours in December to 14.8 hours in June. In mid-June the sun sets around 8:32 PM, and in mid-December around 4:56 PM.
Seasons at Union City
- Warm seasonJun 25 – Sep 28 · highs 79°F+
The warm season lasts about 3.2 months, from Jun 25 to Sep 28, when the average high is 79°F or warmer. Highs peak around Aug 8 at about 81°F.
- Cool seasonNov 29 – Feb 25 · highs 63°F or lower
The cool season runs from Nov 29 to Feb 25, when the average high is 63°F or lower. The coldest nights come around Dec 8, with an average low near 41°F.
- Rainy seasonNov 21 – Mar 26 · 74% of the year's rain
The rainy season runs from Nov 21 to Mar 26, when a day has at least a 20% chance of measurable rain. That stretch brings 74% of the year's rain.
The dark line marks today. Season dates come from the smoothed daily NOAA 1991-2020 normals. Counting from Oct. 1, a typical year has its first inch of rain by Nov 3 and half of its annual total by Jan 26.
Days per year and extremes (Nov 1, 2024 to Oct 31, 2026)
This record runs from Nov 1, 2024 to Oct 31, 2026. Over this record, Union City averaged 6 days a year at 90°F or hotter and no freezing nights. It averaged 10 days a year with at least half an inch of rain and 0 afternoons with wind of 20 mph or more at 2 PM. About 61 mornings a year had 3 or more hours of fog or low cloud.
In the same record, the hottest day was Sep 9, 2026 (98°F) and the coldest night was Jan 27, 2025 (35°F). The wettest day was Nov 23, 2024 (1.18 in.), and the strongest 2 PM gust was 35 mph on Feb 4, 2025.
- 6days at 90°F or hotter
- 0nights at or below freezing
- 10days with ½ in. of rain or more
- 0afternoons with 20+ mph wind
- 61mornings with 3+ hours of fog or low cloud
- Hottest day98°FSep 9, 2026
- Coldest night35°FJan 27, 2025
- Wettest day1.18 inNov 23, 2024
- Strongest 2 PM gust35 mphFeb 4, 2025
What shapes Union City's weather
On summer nights when the marine layer, the cool, damp ocean air beneath the fog, runs deep, low clouds push down the bay. They can bank against the hills behind Union City and hang on there after the flats have cleared. Hikers at Dry Creek Pioneer sometimes start in mist and finish in sun.
Within the city, the low western side around Alvarado is flat, open, and windier. Neighborhoods climbing toward the hills sit farther from the breeze and warm up more by afternoon. On calm nights the pattern reverses, as cold air drains off the slopes and collects on the lowest ground near the creek and the bay. Winter storms send runoff from a large inland watershed down Alameda Creek through town.
Tips for visiting Union City
Take BART to Union Square
Union City station connects to AC Transit and Union City Transit buses.
Hike Dry Creek Pioneer in the morning
Enter from May Road off Mission Boulevard. The hill trails are unpaved and open to the sun, so summer hikes go best early.
Leash dogs when cattle are ahead
Cattle graze the park, and the district asks owners not to let dogs chase them.
Use the creek trail for flat miles
The Alameda Creek Regional Trail is reachable from Union City streets and runs about 12 miles from Niles to the bay.
Union City through the seasons
- Spring (March–May)
- The hills behind town are green, and the Iris Garden beside Dry Creek's main garden opens seasonally in spring.
- Summer (June–August)
- Some mornings start gray against the hills, and then a steady afternoon breeze takes over.
- Fall (September–October)
- September stays as warm as July and August, and the afternoon breeze eases into October. Hillside grass is dry, so days with offshore wind, which blows from the interior toward the coast, call for fire caution.
- Winter (November–February)
- Rain greens the hills and swells Alameda Creek. Unpaved hill trails turn muddy after storms.
Activities and the weather that matters
- Hill hiking at Dry Creek Pioneer: Cool, clear mornings are ideal. Hot afternoons on the open grass are tiring, and the trails get sticky after rain.
- Biking or walking the Alameda Creek Trail: The trail is flat and paved on the south side. Wind is the main variable, lightest in the morning.
- Taking BART to the city: BART is a good choice on breezy or gray days at home, or simply to skip traffic.
Official sources and current conditions
- BART: Union City station
- East Bay Regional Park District: Dry Creek Pioneer
- East Bay Regional Park District: Alameda Creek Regional Trail
- National Weather Service, San Francisco Bay Area forecast office
Numbers on this page come from NOAA data. The text draws on the official sources linked above.
Historical Climate Data
Long-term weather patterns and climate data
Data sources: Recent temperatures come from NOAA URMA and recent precipitation from NOAA Stage IV. Fog, cloud, wind, humidity, and sunshine come from NOAA HRRR, and long-term baselines from NOAA 1991-2020 climate normals.
Climate Overview
Based on NOAA 30-year temperature/rain normals (1991-2020) with recent fog/sun baseline
🌟 Best Months to Visit
⚠️ Challenging Months
Monthly Breakdown
| Month | Comfort | High/Low | ☀️ Sun | 🌫️ Fog | 💧 Rain | Perfect |
|---|---|---|---|---|---|---|
| November 2024 | 84 | 63.8° / 46.6° | 6.5h | 1d | 1.76" | 22 |
| December 2024 | 75 | 61.3° / 46.1° | 4.9h | 6d | 3.55" | 13 |
| January 2025 | 85 | 60.9° / 42.3° | 7.1h | 1d | 0.11" | 25 |
| February 2025 | 79 | 62.3° / 45.2° | 6.5h | 1d | 3.91" | 18 |
| March 2025 | 85 | 63.2° / 47.1° | 8.1h | 0d | 1.33" | 22 |
| April 2025 | 92 | 67° / 49.9° | 9.2h | 1d | 0.25" | 26 |
| May 2025 | 95 | 71.5° / 53° | 11.5h | 1d | 0.16" | 31 |
| June 2025 | 95 | 71.4° / 54.5° | 11.6h | 4d | 0" | 30 |
| July 2025 | 93 | 72.9° / 57.7° | 10.6h | 6d | 0" | 31 |
| August 2025 | 91 | 77.5° / 59.5° | 9.9h | 5d | 0" | 30 |
| September 2025 | 91 | 77.9° / 62.1° | 8.9h | 1d | 0.08" | 28 |
| October 2025 | 89 | 72.3° / 55.3° | 7.8h | 3d | 1.32" | 25 |
| November 2025 | 80 | 65.2° / 50.3° | 6.2h | 7d | 2.39" | 16 |
| December 2025 | 73 | 59.5° / 45.3° | 4.9h | 9d | 2.44" | 7 |
| January 2026 | 81 | 62.8° / 44.2° | 6.5h | 3d | 2.61" | 23 |
| February 2026 | 81 | 64.6° / 47.9° | 6.8h | 4d | 2.77" | 19 |
| March 2026 | 94 | 76° / 52.5° | 9.5h | 1d | 0.02" | 30 |
| April 2026 | 86 | 67.8° / 51.8° | 8.3h | 0d | 2.79" | 23 |
| May 2026 | 93 | 70.4° / 54.1° | 10.8h | 4d | 0.45" | 28 |
| June 2026 | 94 | 74.5° / 57.2° | 11.4h | 1d | 0.01" | 30 |
| July 2026 | 93 | 74.9° / 58.9° | 10.5h | 2d | 0" | 31 |
| August 2026 | 93 | 76.2° / 59.2° | 10.2h | 5d | 0" | 31 |
| September 2026 | 93 | 76.5° / 58.3° | 9.8h | 1d | 0.06" | 28 |
| October 2026 | 90 | 75.2° / 54.5° | 7.9h | 2d | 0.21" | 29 |
Climate Trends
Average Temperature by Month
About the Union City climate charts
The temperature chart compares average monthly highs and lows at Union City, showing both the seasonal cycle and the typical day-to-night range. The comfort chart summarizes how often the combined weather pattern is favorable rather than judging temperature alone.
Precipitation shows the total recorded or modeled rainfall for each month at Union City. Sunshine compares average bright-sky hours with the daylight available, while fog shows the average number of morning fog or low-cloud hours per day. Switch between the chart tabs to compare the same months across each measure.
Hourly Temperature, Fog, Wind, Cloud Cover, and Solar Radiation Patterns
Average local hour by month from 2014-09-30 to 2026-04-30
- Temperature: At Union City, the warmest typical hour is 3 PM in August (77°F). The coldest is 7 AM in January (45°F).
- Fog: Fog or low cloud covers Union City in 27% of 8 AM hours in July, the foggiest month. It usually thins to a third of that by 11 AM. April mornings are the least foggy (9%).
- Wind: From February through October, wind at Union City typically builds after 1 PM. In May it peaks around 5 PM, averaging 11 mph with 3% of those hours windy, while mornings average 4 mph.
- Cloud Cover: August middays are the clearest at Union City (13% average cloud cover), and December middays are the cloudiest (33%).
- Solar Radiation: The strongest typical sun at Union City comes at 1 PM in June, averaging 963 W/m².
How to read the hourly heatmaps for Union City
This heatmap shows how average temperature at Union City changes by hour and month. Read left to right for the seasons and top to bottom for the time of day. Warmer colors mark the usual afternoon peaks, and cooler colors show overnight and winter lows.
This heatmap shows when fog or low cloud is most likely at Union City. Darker cells mark the months and hours when fog has been most common. They help separate overnight or morning fog from cloud that tends to linger into the afternoon.
This heatmap shows the typical hourly wind pattern at Union City through the year. It makes recurring afternoon wind, calmer overnight periods, and seasonal changes easier to compare than a single daily wind value.
This heatmap shows average cloud cover at Union City for every month and hour. Use it to see whether cloudiness is mainly an overnight and morning pattern or commonly persists during the part of the day you plan to visit.
This heatmap shows the average solar radiation reaching Union City by month and hour. Brighter cells indicate the strongest typical sun, while muted cells can reflect nighttime, shorter winter days, cloud cover, smoke, or terrain shading.
Each cell combines one month with one local hour. Hover over or focus on a cell for its value and sample coverage. The red marker shows the current month and hour.
How recent months compared at Union City
- October 2026 recap: October 2026 at Union City averaged a high of 75°F, 3°F warmer than October 2025 (72°F).
- Rain year: The 2025-26 rain year (Oct. 1 to Sep. 30) brought 14.9 in. of rain to Union City, 81% of the 18.3 in. normal.
Location Details
Union City weather questions
Everything you need to know about weather and visiting Union City
What is the weather like at Union City today?
It's 53°F at Union City right now, with a comfort score of 77 (great). Monday's forecast high at Union City is 56°F, 10°F below the mid November normal of 66°F. The best window today is 9 AM to noon, at about 55°F with a 4 mph wind (comfort 58).
What is the best month to visit Union City?
By typical temperature, wind, cloud, humidity, and rain odds, the most comfortable months at Union City are August, September, and June. The best hours are usually 11 AM to 2 PM in August, 11 AM to 2 PM in September, and 11 AM to 2 PM in June. The warm season lasts about 3.2 months, from Jun 25 to Sep 28, when the average high is 79°F or warmer. Highs peak around Aug 8 at about 81°F.
What are the warmest and coldest months at Union City?
August is the warmest month at Union City, with an average high of 81°F. December is the coldest, with an average low of 41°F.
When does the fog burn off at Union City?
Fog or low cloud covers Union City in 27% of 8 AM hours in July, the foggiest month. It usually thins to a third of that by 11 AM. April mornings are the least foggy (9%).
When is it windiest at Union City?
From February through October, wind at Union City typically builds after 1 PM. In May it peaks around 5 PM, averaging 11 mph with 3% of those hours windy, while mornings average 4 mph.
How much rain does Union City get?
December is the wettest month (3.6 in.), out of about 18.3 in. a year. The rainy season runs from Nov 21 to Mar 26, when a day has at least a 20% chance of measurable rain. That stretch brings 74% of the year's rain. The 2025-26 rain year (Oct. 1 to Sep. 30) brought 14.9 in. of rain to Union City, 81% of the 18.3 in. normal.
How does Union City weather compare with Coyote Hills Regional Park?
Coyote Hills Regional Park, 3.7 miles away, runs about 13°F cooler than Union City on summer afternoons.
What kind of place is Union City?
Union City fills the gap between Hayward and Fremont, from the bay plain up to the first grassy hills of the East Bay ridge. It was incorporated in 1959 by joining Alvarado, Decoto, and New Haven, and Alvarado was Alameda County's original county seat. Alameda Creek crosses town on its way to the bay, and BART stops at Union Square. Dry Creek Pioneer Regional Park climbs the slopes behind the city from its May Road entrance.
What is Union City weather like in November?
November at Union City averages a high of 66°F and a low of 45°F, with 1.8 in. of rain over about 6 rainy days. Afternoon wind averages 5 mph.
More about Union City weather
Guides that explain the weather here and nearby
Data sources and methods
- Monthly temperatures and precipitation: NOAA 1991-2020 normals.
- Fog, cloud, wind, sun, and comfort by hour and month: NOAA's HRRR hourly analysis from September 2014 to April 2026.
- Daily records and recent months: NOAA URMA and HRRR analyses, plus NOAA Stage IV precipitation.
- Nearby comparisons and regional rankings use the same hourly HRRR summaries for every destination in the region.
- Alerts: National Weather Service. Tides and ocean temperature: NOAA CO-OPS, where shown.
- All statements on this page are computed from these datasets, apart from the “What shapes the weather” guide, which cites its sources inline.
- BART, Union City Station (accessed 2026-10-27)
- East Bay Regional Park District, Dry Creek Pioneer Regional Park (accessed 2026-10-27)
- East Bay Regional Park District, Alameda Creek Regional Trail (accessed 2026-10-27)
Rendered 2026-11-15T12:04:18.093Z.