Castro Valley Weather
Town • San Francisco Bay Area
Castro Valley is an unincorporated community governed by Alameda County, which describes it as a populated valley surrounded by hills. It lies one ridge back from the bay, between San Leandro and Hayward, with Interstate 580 and Castro Valley Boulevard running through its center. East Bay Regional Park District lands, including Lake Chabot, line its northern edge. Voters limited development in the canyonlands that ring it, so open grass and oak country starts at the end of many streets.
Plan your week
10-Day Forecast
Hour by hour
Hourly Forecast
Current Conditions
Comfort Breakdown
Castro Valley weather today and through the year
It's 53°F at Castro Valley right now (feels like 50°F), with 5 mph wind and a comfort score of 77. Monday's forecast high at Castro Valley is 55°F, 10°F below the mid November normal of 65°F. The best window today is 9 AM to noon, at about 54°F with a 5 mph wind (comfort 57).
August is the warmest month at Castro Valley, with an average high of 80°F. December is the coldest, with an average low of 41°F. December is the wettest month (3.8 in.), out of about 19.6 in. a year. By typical temperature, wind, cloud, humidity, and rain odds, the most comfortable months at Castro Valley are September, June, and August. The best hours are usually 11 AM to 2 PM in September, 11 AM to 2 PM in June, and 11 AM to 2 PM in August.
A low ridge separates Castro Valley from the San Leandro flats. Summer ocean air that crosses the bay has to climb over it. Afternoons run a little warmer than in San Leandro or west Hayward, only a few miles away. Morning fog comes about as often in all three places. The valley still gets enough of the sea breeze to avoid the full heat of the Diablo Valley.
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 Castro Valley 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 54°F with a 5 mph wind (comfort 57).
Best day this week
Of the next 7 days, Friday looks best for Castro Valley, with a 61°F high and midday comfort near 80. Thursday looks weakest (46).
Rain
Next good chance of rain: today (77%, about 0.27 in.).
Live weather map
Weather around Castro Valley right now
Overcast and 53° at Castro Valley right now.
About the live weather map for Castro Valley
The map centers on Castro Valley 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.
Castro Valley vs nearby places
Typical summer conditions compared with Castro Valley, 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 Castro Valley |
|---|---|---|---|---|---|
| Hayward | 1.8 mi | -2°F | 24% | 9 mph | a very similar climate |
| Anthony Chabot Regional Park | 3.7 mi | -3°F | 39% | 10 mph | more summer morning fog (39% vs 26% of morning hours) |
| San Leandro | 4.4 mi | -2°F | 28% | 9 mph | a very similar climate |
| Pacifica | 22.6 mi | -20°F | 56% | 9 mph | about 20°F cooler on summer afternoons and more summer morning fog (56% vs 26% of morning hours) |
| Baker Beach | 22.8 mi | -19°F | 45% | 16 mph | about 19°F cooler on summer afternoons and windier summer afternoons (16 vs 9 mph) |
| Ocean Beach | 23.6 mi | -19°F | 49% | 11 mph | about 19°F cooler on summer afternoons and more summer morning fog (49% vs 26% of morning hours) |
Places with a climate like Castro Valley's
- Edgewood Park & Natural Preserve (19 mi away): similar temperatures through the year
- Mountain View (21 mi away): similar temperatures through the year
- Orinda (14 mi away): similar temperatures through the year
Climate Dashboard
Current conditions vs. NOAA normals and recent destination baseline
What the Castro Valley climate comparisons mean
These cards compare recent conditions at Castro Valley 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 Castro Valley 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.
Castro Valley weather by month
August is the warmest month at Castro Valley, with an average high of 80°F. December is the coldest, with an average low of 41°F. December is the wettest month (3.8 in.), out of about 19.6 in. a year. Morning fog peaks in July, when fog or low cloud covers 29% of the hours from 6 to 10 AM. August has the clearest middays, with clouds covering about 14% of the sky from 11 AM to 3 PM.
By typical temperature, wind, cloud, humidity, and rain odds, the most comfortable months at Castro Valley are September, June, and August. The best hours are usually 11 AM to 2 PM in September, 11 AM to 2 PM in June, and 11 AM to 2 PM in August.
| Month | Avg high | Avg low | Rain | Rainy days | Morning fog | Midday cloud | Afternoon wind | Daylight | Comfort |
|---|---|---|---|---|---|---|---|---|---|
| Jan | 58°F | 41°F | 3.8 in | 8 | 12% | 33% | 5 mph | 9.8 h | 60 |
| Feb | 62°F | 44°F | 3.6 in | 8 | 9% | 26% | 7 mph | 10.7 h | 64 |
| Mar | 65°F | 45°F | 2.9 in | 7 | 12% | 32% | 8 mph | 11.9 h | 66 |
| Apr | 68°F | 47°F | 1.5 in | 5 | 13% | 26% | 9 mph | 13.2 h | 75 |
| May | 72°F | 50°F | 0.7 in | 3 | 14% | 25% | 10 mph | 14.2 h | 79 |
| Jun | 78°F | 54°F | 0.1 in | 2 | 23% | 15% | 9 mph | 14.8 h | 90 |
| Jul | 80°F | 56°F | 0.0 in | 0 | 29% | 14% | 9 mph | 14.5 h | 89 |
| Aug | 80°F | 56°F | 0.0 in | 1 | 26% | 14% | 8 mph | 13.6 h | 90 |
| Sep | 80°F | 55°F | 0.1 in | 2 | 16% | 16% | 8 mph | 12.3 h | 91 |
| Oct | 75°F | 51°F | 0.9 in | 4 | 11% | 18% | 6 mph | 11.1 h | 86 |
| Nov | 65°F | 45°F | 2.0 in | 6 | 9% | 22% | 5 mph | 10.1 h | 78 |
| Dec | 58°F | 41°F | 3.8 in | 8 | 13% | 34% | 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.
What makes Castro Valley's weather different
When the fog burns off
11 AMwhen July fog usually thins (39% foggy at 8 AM)
Fog or low cloud covers Castro Valley in 39% of 8 AM hours in July, the foggiest month. It usually thins to a third of that by 11 AM. November mornings are the least foggy (9%).
When the wind picks up
1 PMwhen afternoon wind builds, March–October
From March through October, wind at Castro Valley typically builds after 1 PM. In May it peaks around 4 PM, averaging 10 mph with 1% of those hours windy, while mornings average 5 mph.
Daylight
9.6–14.8 hof daylight, Dec to Jun
Days at Castro Valley 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 Castro Valley
- Warm seasonJun 26 – Sep 28 · highs 78°F+
The warm season lasts about 3.1 months, from Jun 26 to Sep 28, when the average high is 78°F or warmer. Highs peak around Aug 8 at about 80°F.
- Cool seasonNov 28 – Feb 26 · highs 63°F or lower
The cool season runs from Nov 28 to Feb 26, 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 16 – Mar 31 · 77% of the year's rain
The rainy season runs from Nov 16 to Mar 31, when a day has at least a 20% chance of measurable rain. That stretch brings 77% 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 2 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, Castro Valley averaged 12 days a year at 90°F or hotter and no freezing nights. It averaged 14 days a year with at least half an inch of rain and 1 afternoon with wind of 20 mph or more at 2 PM. About 91 mornings a year had 3 or more hours of fog or low cloud.
In the same record, the hottest day was Sep 9, 2026 (100°F) and the coldest night was Feb 10, 2025 (37°F). The wettest day was Apr 21, 2026 (1.81 in.), and the strongest 2 PM gust was 43 mph on Mar 12, 2025.
- 12days at 90°F or hotter
- 0nights at or below freezing
- 14days with ½ in. of rain or more
- 1afternoon with 20+ mph wind
- 91mornings with 3+ hours of fog or low cloud
- Hottest day100°FSep 9, 2026
- Coldest night37°FFeb 10, 2025
- Wettest day1.81 inApr 21, 2026
- Strongest 2 PM gust43 mphMar 12, 2025
What shapes Castro Valley's weather
Castro Valley's hills shape its nights as well. On clear, calm nights cool air slides down side canyons such as Crow, Cull and Palomares and settles on the valley floor. Winter mornings along the boulevard are often colder than on the bayshore, where open water keeps the air milder.
Elevation varies a lot within the community. Upper neighborhoods such as Five Canyons and the ridges near Greenridge Park sit well above the valley floor. They catch more wind and more of the winter rain that falls heaviest on the East Bay hills. Offshore wind is the dry wind that blows from inland toward the coast. On those days, late-summer heat and the dry grass of the canyonlands make fire the main concern.
Tips for visiting Castro Valley
Use Castro Valley BART
Castro Valley station, near the center of town, is on BART's Dublin/Pleasanton line.
Go to Greenridge Park for the overview
The county's general plan points to Greenridge Park for panoramic views of Castro Valley and beyond, the easiest way to see how the hills enclose the valley.
Lake Chabot is for boats, not swimming
Swimming is never permitted at Lake Chabot, which is a standby emergency water supply. Rent a rowboat, pedal boat, or kayak instead.
Walk the lake's paved shore early
The paved West Shore and East Shore trails total about 3.5 miles. Summer mornings are cooler and calmer than afternoons.
Castro Valley through the seasons
- Spring (March–May)
- The canyonlands turn green and afternoons are comfortable. Spring is a good time for the longer trails linking Lake Chabot to Anthony Chabot before the grass dries.
- Summer (June–August)
- Mornings may start gray, but the fog usually thins by late morning and afternoons are warm. Lake Chabot's gates stay open until 9 p.m. from May through Labor Day.
- Fall (September–October)
- Fall is warm and dry, and fire season peaks in the surrounding canyons until the first soaking rain.
- Winter (November–February)
- Winter mornings on the valley floor are often colder than on the bayshore, with occasional frost after clear nights. Rain falls more heavily on the ridges around the valley.
Activities and the weather that matters
- Boating on Lake Chabot: Calm mornings are best for rowing and kayaking. Afternoon wind can chop up the water on summer days.
- Fishing: Lake Chabot is stocked with trout and catfish and also holds bass and crappie. Cool, overcast mornings tend to be the comfortable time to fish.
- Hill hiking: More than 20 miles of Lake Chabot trails connect to Anthony Chabot's network. Spring is ideal, and summer afternoons on open slopes are hot.
Official sources and current conditions
- East Bay Regional Park District: Lake Chabot
- BART: Castro Valley station
- Alameda County: Castro Valley General Plan introduction
- East Bay Regional Park District: Alerts and closures
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 | 83 | 63.8° / 47.8° | 6.5h | 1d | 2.51" | 20 |
| December 2024 | 74 | 61.5° / 47.1° | 5h | 5d | 5.3" | 12 |
| January 2025 | 85 | 61.2° / 43.8° | 7h | 3d | 0.17" | 24 |
| February 2025 | 78 | 62.3° / 45.8° | 6.6h | 0d | 5.56" | 17 |
| March 2025 | 84 | 63.2° / 47.1° | 8.2h | 2d | 1.73" | 23 |
| April 2025 | 91 | 67.3° / 49.9° | 9.2h | 4d | 0.28" | 25 |
| May 2025 | 93 | 72° / 53.1° | 11.3h | 3d | 0.28" | 31 |
| June 2025 | 92 | 71.6° / 53.9° | 11h | 12d | 0" | 29 |
| July 2025 | 91 | 73° / 57° | 10.3h | 11d | 0" | 30 |
| August 2025 | 91 | 78.4° / 59.2° | 10.2h | 11d | 0" | 30 |
| September 2025 | 90 | 78.3° / 61.7° | 9h | 3d | 0.2" | 27 |
| October 2025 | 89 | 72.6° / 55.9° | 7.9h | 2d | 1.82" | 25 |
| November 2025 | 81 | 66.1° / 50.9° | 6.2h | 5d | 3.68" | 21 |
| December 2025 | 74 | 59.5° / 45.6° | 5.2h | 2d | 3.55" | 13 |
| January 2026 | 82 | 63.6° / 46.2° | 6.6h | 2d | 3.67" | 22 |
| February 2026 | 80 | 64.8° / 48.6° | 6.4h | 4d | 4.1" | 18 |
| March 2026 | 94 | 77.1° / 54.1° | 9.5h | 1d | 0.06" | 29 |
| April 2026 | 86 | 67.8° / 51.7° | 8.9h | 3d | 4.79" | 24 |
| May 2026 | 91 | 70.8° / 53.9° | 10.7h | 5d | 0.4" | 29 |
| June 2026 | 93 | 74.6° / 56.6° | 11.5h | 7d | 0.03" | 29 |
| July 2026 | 92 | 75.5° / 58.5° | 10.4h | 10d | 0" | 30 |
| August 2026 | 91 | 77° / 58.7° | 10.1h | 9d | 0" | 31 |
| September 2026 | 91 | 76.7° / 58.5° | 9.6h | 4d | 0.14" | 28 |
| October 2026 | 90 | 76.3° / 55.8° | 8.1h | 2d | 0.39" | 29 |
Climate Trends
Average Temperature by Month
About the Castro Valley climate charts
The temperature chart compares average monthly highs and lows at Castro Valley, 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 Castro Valley. 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 Castro Valley, the warmest typical hour is 3 PM in August (79°F). The coldest is 7 AM in December (45°F).
- Fog: Fog or low cloud covers Castro Valley in 39% of 8 AM hours in July, the foggiest month. It usually thins to a third of that by 11 AM. November mornings are the least foggy (9%).
- Wind: From March through October, wind at Castro Valley typically builds after 1 PM. In May it peaks around 4 PM, averaging 10 mph with 1% of those hours windy, while mornings average 5 mph.
- Cloud Cover: August middays are the clearest at Castro Valley (14% average cloud cover), and December middays are the cloudiest (34%).
- Solar Radiation: The strongest typical sun at Castro Valley comes at 1 PM in June, averaging 962 W/m².
How to read the hourly heatmaps for Castro Valley
This heatmap shows how average temperature at Castro Valley 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 Castro Valley. 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 Castro Valley 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 Castro Valley 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 Castro Valley 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 Castro Valley
- October 2026 recap: October 2026 at Castro Valley averaged a high of 76°F, 2°F warmer than the 1991-2020 normal of 75°F. It brought 0.39 in. of rain, compared with a normal of 0.92 in.
- Rain year: The 2025-26 rain year (Oct. 1 to Sep. 30) brought 22.2 in. of rain to Castro Valley, 113% of the 19.6 in. normal.
Location Details
Castro Valley weather questions
Everything you need to know about weather and visiting Castro Valley
What is the weather like at Castro Valley today?
It's 53°F at Castro Valley right now, with a comfort score of 77 (great). Monday's forecast high at Castro Valley is 55°F, 10°F below the mid November normal of 65°F. The best window today is 9 AM to noon, at about 54°F with a 5 mph wind (comfort 57).
What is the best month to visit Castro Valley?
By typical temperature, wind, cloud, humidity, and rain odds, the most comfortable months at Castro Valley are September, June, and August. The best hours are usually 11 AM to 2 PM in September, 11 AM to 2 PM in June, and 11 AM to 2 PM in August. The warm season lasts about 3.1 months, from Jun 26 to Sep 28, when the average high is 78°F or warmer. Highs peak around Aug 8 at about 80°F.
What are the warmest and coldest months at Castro Valley?
August is the warmest month at Castro Valley, with an average high of 80°F. December is the coldest, with an average low of 41°F.
When does the fog burn off at Castro Valley?
Fog or low cloud covers Castro Valley in 39% of 8 AM hours in July, the foggiest month. It usually thins to a third of that by 11 AM. November mornings are the least foggy (9%).
When is it windiest at Castro Valley?
From March through October, wind at Castro Valley typically builds after 1 PM. In May it peaks around 4 PM, averaging 10 mph with 1% of those hours windy, while mornings average 5 mph.
How much rain does Castro Valley get?
December is the wettest month (3.8 in.), out of about 19.6 in. a year. The rainy season runs from Nov 16 to Mar 31, when a day has at least a 20% chance of measurable rain. That stretch brings 77% of the year's rain. The 2025-26 rain year (Oct. 1 to Sep. 30) brought 22.2 in. of rain to Castro Valley, 113% of the 19.6 in. normal.
What kind of place is Castro Valley?
Castro Valley is an unincorporated community governed by Alameda County, which describes it as a populated valley surrounded by hills. It lies one ridge back from the bay, between San Leandro and Hayward, with Interstate 580 and Castro Valley Boulevard running through its center. East Bay Regional Park District lands, including Lake Chabot, line its northern edge. Voters limited development in the canyonlands that ring it, so open grass and oak country starts at the end of many streets.
What is Castro Valley weather like in November?
November at Castro Valley averages a high of 65°F and a low of 45°F, with 2.0 in. of rain over about 6 rainy days. Afternoon wind averages 5 mph.
More about Castro Valley 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.
- Alameda County, Castro Valley General Plan, Chapter 1: Introduction (accessed 2026-10-27)
- East Bay Regional Park District, Lake Chabot Regional Park (accessed 2026-10-27)
- BART, Castro Valley station (accessed 2026-10-27)
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