You’ve probably already glanced at your phone and seen that "79°F" staring back at you for Sunday, January 18, 2026. Honestly, it feels a bit like a prank. We are deep in the middle of January, yet San Bernardino is about to feel more like a late May afternoon. It’s that classic Inland Empire trick where you walk out the door in a parka at 7:00 AM and find yourself sweating through your t-shirt by lunchtime.
Basically, tomorrow is going to be a day of extremes.
The San Bernardino weather for tomorrow is defined by a massive 33-degree swing. We’re looking at a high of 79°F and a low of 46°F. If you aren’t dressing in layers, you’re doing it wrong. This isn't just about "nice weather"; it’s about the specific topography of our valley and how the air settles when the sun goes down.
What’s actually happening with the clouds tomorrow?
Don't expect a perfectly crisp, blue-sky day. The forecast is calling for cloudy conditions during the day. This is actually a bit of a relief because 79 degrees under a direct, beating sun in the IE can feel much hotter than the thermometer suggests. These clouds will likely act as a bit of a lid, keeping things from getting truly scorching, but don't let them fool you—the UV index is sitting at 2. It’s low, sure, but if you’re out at Glen Helen or hiking the foothills for three hours, that exposure still adds up.
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By the time night rolls around, those clouds are going to clear out completely.
When the sky goes clear tomorrow night, that’s when the temperature is going to tank. Without the cloud cover to trap the day's heat, all that warmth from the 79-degree afternoon is going to radiate straight back into space. That’s how we end up at 46°F. It’s a dry chill, too. With humidity at 20%, the air is going to feel "thin" and crisp.
The "Rain" Question
Everyone sees the 10% chance of rain and wonders if they should cancel their outdoor plans. Honestly? Probably not. A 10% chance of precipitation in San Bernardino usually means a stray sprinkle or just a bit of "virga"—rain that evaporates before it even hits the pavement.
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- Daytime rain chance: 10% (mostly a "maybe")
- Nighttime rain chance: 0% (bone dry)
Basically, you can leave the umbrella at home. What you should be more concerned about is the wind. We’re looking at a 6 mph wind coming from the north. It’s not a full-blown Santa Ana event, but a steady north wind in January usually brings that dry, desert air that makes your skin feel like parchment paper.
Why the Inland Empire gets these crazy swings
A lot of people think the "San Bernardino weather for tomorrow" is just typical Southern California vibes, but experts like those at the National Weather Service often point to the "Inland Heat Sink" effect. Because we are boxed in by the San Bernardino and San Gabriel mountains, we don't get the immediate coastal cooling that Los Angeles enjoys. The air gets trapped. It heats up fast. Then, because we’re at a slightly higher elevation than the coast, the "radiational cooling" at night is much more aggressive.
If you’re heading out to the National Orange Show Event Center or just grabbing a coffee on Hospitality Lane, the morning is going to feel "brisk" (46 degrees is no joke). By 2:00 PM, you’ll be looking for the A/C.
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Practical steps for surviving Sunday
Don't just look at the high of 79 and assume it's "summer." That’s how people end up caught off guard when the sun dips behind the mountains.
- Hydrate more than usual. 20% humidity is very dry. You won't feel yourself sweating because it evaporates instantly, but you're losing water.
- The "Layer Cake" strategy. Wear a light hoodie over a t-shirt. You’ll need the hoodie until about 10:30 AM, then you’ll want it again by 5:30 PM.
- Moisturize. That north wind combined with low humidity is a recipe for chapped lips and dry hands.
- Check your tires. Large temperature swings (from 46 to 79) can actually mess with your tire pressure light. If it pops on in the morning, don't panic—it might just be the cold air "shrinking" before the day warms up.
Tomorrow is looking like a beautiful, if slightly schizophrenic, California winter day. Enjoy the warmth while it lasts, because as any local knows, these 80-degree January "teases" are usually followed by a sudden shift back to the damp, gray reality of late winter.
Keep an eye on the wind speeds if you're in the North End or near the Cajon Pass, as that 6 mph north wind can occasionally gust a bit higher in the canyons. Otherwise, it’s a solid day for a car wash or a quick mountain run—just keep that heater/AC dial ready for a workout.