Honestly, if you've lived in the East Bay for more than a week, you know the drill. You wake up in Castro Valley and it’s basically a guessing game whether you need a heavy puffer jacket or just a light hoodie to get through the day. Right now, as we’re sitting in the middle of January 2026, the microclimates are doing that weird thing they always do.
One minute you’re looking at the fog rolling over the Fairmont Ridge, and the next, the sun is hitting Lake Chabot just right.
Let's get into the actual numbers for the 10 day forecast castro valley ca because the data is actually kind of surprising for this time of year. Today, Sunday, January 18, we're looking at a high of 64°F. That’s a bit warmer than the usual January average of 58°F. It’s mostly cloudy right now with a low of 47°F tonight. If you're heading out, just know there's a tiny 10% chance of rain, but it’s mostly just going to be grey.
The Week Ahead: Sun, Clouds, and That Weird Humidity
Tomorrow, Monday the 19th, is actually looking like the pick of the week. We’re hitting 64°F again, but it’ll be full-on sunny. It’s the kind of day where you think spring is coming early, but then the sun drops and it hits 44°F. You’ve been warned.
📖 Related: Finding the Right Words: Quotes About Sons That Actually Mean Something
Here is the breakdown of what the next several days look like:
- Tuesday, Jan 20: Mostly cloudy, high of 60°F, low of 44°F.
- Wednesday, Jan 21: Solidly cloudy, holding at 60°F / 46°F.
- Thursday, Jan 22: The sun comes back! High 60°F, low 45°F.
- Friday, Jan 23: Partly sunny, 60°F / 44°F.
- Saturday, Jan 24: A bit cooler at 59°F, with a slightly higher 15% rain chance during the day.
Why the 10 day forecast castro valley ca is Never Quite What it Seems
The thing about Castro Valley is the elevation change. If you're up in the Five Canyons area, you might be shivering while someone down by the Boulevard is perfectly comfortable.
Experts like those at the National Weather Service often talk about the "marine layer" influence, but in January, it’s more about the storm tracks coming off the Pacific. We’re seeing a very calm pattern right now. Wind speeds are hovering around 3 to 6 mph, mostly coming from the northeast. It’s not the "windy" season yet, which usually hits harder in the spring.
👉 See also: Williams Sonoma Deer Park IL: What Most People Get Wrong About This Kitchen Icon
The humidity is staying pretty high, around 75% today. That’s why the air feels "heavy" even when it isn't raining. It’s that classic Northern California dampness that gets into your bones if you aren't moving around.
Planning Your Outdoor Time
If you're trying to hit the trails at Cull Canyon or Lake Chabot, aim for Monday or Thursday. Those are your best bets for clear skies. By the time we get to next Sunday, January 25, things stay mild but get a little cooler with a high of 58°F.
Looking toward the end of the month, the trend stays pretty consistent. Monday the 26th and Tuesday the 27th are hovering in that 59°F range. It’s not "cold" by East Coast standards, but for us? It’s definitely "wear your thick socks" weather.
✨ Don't miss: Finding the most affordable way to live when everything feels too expensive
A lot of people think January is just constant rain in the Bay Area. While it’s historically our wettest month, this specific window is actually looking pretty dry. We've only got about a 5% to 10% chance of precipitation most days.
Actionable Insights for the Next 10 Days:
- Layering is mandatory: With 20-degree swings between day and night (64°F to 44°F), don't leave the house without a shell.
- Morning visibility: With the high humidity (75-79%) and cool lows, expect some morning patchy fog, especially near the canyons.
- Garden check: Since it’s staying dry and relatively "warm" during the day, keep an eye on your potted plants; they might actually need a drink despite it being mid-winter.
- Best day for a hike: Monday, January 19. It’s the clearest and warmest day in the immediate forecast.
Stay dry (or mostly just cloudy) out there.