Honestly, if you're looking at the Rancho Cucamonga weather forecast and expecting a standard "Southern California winter," you're probably going to be a little surprised. This city doesn't play by the same rules as Santa Monica or even downtown L.A.
We're sitting right at the base of the San Gabriel Mountains. That's not just a pretty backdrop for your Instagram photos; it’s a literal weather machine. The mountains trap air, funnel winds, and create a microclimate that can swing from "balmy t-shirt weather" to "where did I put my parka?" in about three hours flat.
The Current Situation: January 15, 2026
Right now, as of Thursday morning, things are looking pretty spectacular, but there's a catch. The temperature is sitting at 57°F with a crisp northwest wind at 7 mph.
Basically, it's perfect walking weather.
If you’re heading out to Victoria Gardens today, expect a high of 76°F. That’s a massive jump from the morning low. We’re looking at a super dry day—humidity is hovering around 31%—and the sky is basically a solid sheet of blue. There’s a tiny 10% chance of rain during the day, but don't hold your breath for it. It’s mostly just "chamber of commerce" weather for the rest of today.
Tonight, it drops back down to a chilly 54°F. If you’re at an outdoor dinner, you’ll definitely want a layer.
Why the Wind Matters More Than the Temp
You can't talk about Rancho Cucamonga without talking about the wind. Specifically, the Santa Anas.
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A few days ago, on January 13, we saw some wild reports. While the city itself was breezy, nearby spots like Cloudland Cutoff clocked gusts at 68 mph. That is no joke. Even in the city proper, it’s common to see 30 mph gusts that will knock your patio umbrella into the neighbor's pool.
The forecast for the next few days shows the wind calming down, shifting mostly from the northwest to the north at a gentle 4 to 6 mph. But here's the thing: in Rancho, the wind is the boss. When the high pressure builds over the Great Basin, those winds come screaming through the Cajon Pass. It dries everything out, spikes the fire danger, and makes your hair look like you’ve been sticking your head out of a moving car.
Looking Ahead: The 10-Day Outlook
If you're planning your week, here's the deal.
Friday, January 16, is basically a carbon copy of today. High of 76°F, low of 52°F. Sunny and dry.
Then, Saturday hits a little differently. It's going to get cloudy. The high drops to 73°F, and the humidity stays low at 23%. It's that weird, "gray but dry" kind of day that happens in the Inland Empire.
The rest of the week stays in that comfortable 68°F to 73°F range.
- Monday, Jan 19: Mostly sunny, high of 73°F.
- Wednesday, Jan 21: High of 68°F.
- Next Friday, Jan 23: Things start to shift. We’re looking at a high of only 62°F and a 25% chance of rain at night.
What Most People Miss
People think California doesn't have seasons. We do; they're just subtle.
January in Rancho Cucamonga is technically the "cool season," but our average highs are still in the mid-60s. However, the record highs can hit the 80s, and the record lows can dip into the 30s.
Also, can we talk about the rain? When it rains here, it rains. We’re currently in a dry spell, but the historical average for January is about 2.3 to 3.2 inches. Most of that usually comes in one or two big "Atmospheric River" events rather than a steady drizzle.
If you’re a gardener in the 91701 or 91730 zip codes, keep an eye on that humidity. When it drops to 12% (like it's predicted to on Sunday, January 25), your plants are going to be thirsty. The air gets incredibly "static-y" too. You’ll be shocking yourself on every doorknob in the house.
Practical Advice for the Week
Stop checking the "daily high" and start checking the "hourly swing."
If you leave the house at 7:00 AM, it's 50 degrees. By 2:00 PM, it's 76. That is a 26-degree difference. You need a system. I’m talking a light base layer, a sweater, and a shell.
Also, watch the dust. Those north winds bring in all the particulate matter from the desert and the mountains. If you have allergies, this week might be a bit rough even with the clear skies.
Keep your tires properly inflated, too. These temperature swings—20+ degrees in a few hours—can actually trip your TPMS light because air density changes that fast.
Basically, enjoy the sun while it's here, keep a jacket in the car for the 5:00 PM sunset chill, and maybe don't wash your car until after the Saturday clouds pass.
Next Steps for You:
- Check your irrigation timers; the low humidity (below 25%) this weekend means your lawn needs a drink even if it feels "cool."
- Prep for a temperature drop late next week (Jan 22-23) by digging out your heavier coats now.
- If you’re driving the 15 or 210 freeways, stay alert for sudden crosswinds near the North Etiwanda Preserve.