Honestly, looking at the Tustin weather forecast for the next week and a half is kinda like watching a slow-motion transformation of a Southern California winter. You’ve probably heard people say Orange County doesn't have seasons, but if you actually live here, you know that’s not true. It’s just... subtle.
Right now, as of Sunday morning, January 18, 2026, we are sitting at a cool 57°F. It’s mostly cloudy. You can feel that 30% humidity keeping things crisp but not bone-dry. The wind is barely a whisper, coming from the east at about 4 mph.
But here is where it gets interesting.
The Immediate Heat Spike
Today is actually going to be a bit of an outlier. We are looking at a high of 78°F under sunny skies. That is nearly 10 degrees above the historical average high of 68°F for Tustin in January. It’s that classic "winter in the OC" vibe where you’re wearing a hoodie at 7:00 AM and wondering if you should have grabbed shorts by noon.
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Tomorrow, Monday, stays warm at 76°F, and Tuesday holds onto the sun with a high of 75°F.
If you're planning on being outdoors or heading toward the old blimp hangars for a walk, these next 72 hours are your gold mine. The UV index is peaking around 3, so it's not "summer burn" territory, but it’s definitely bright.
The Mid-Week Shift and Rain Chances
By Wednesday, the script flips. Basically, the marine layer and some cloud cover start moving in. Temperatures drop to 70°F on Wednesday and then a much more "wintery" 65°F on Thursday.
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You’ll want to keep an eye on Thursday night.
The forecast shows a 25% chance of light rain once the sun goes down. It’s not a deluge—just enough to make the 5 freeway a bit of a mess for the Friday morning commute.
Looking at the Full 10 Day Stretch
The back half of the weather Tustin CA 10 day forecast is where things settle into a predictable, cool pattern.
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- Friday, Jan 23: Partly sunny and 63°F. High humidity at 67% makes it feel a bit damp.
- Saturday, Jan 24: Light rain is actually in the cards during the day with a 20% chance. High of 66°F.
- Sunday, Jan 25: Mostly cloudy, staying cool at 65°F.
- Monday, Jan 26: The sun starts peaking back through. 66°F.
- Tuesday, Jan 27: A slight warm-up begins again, hitting 71°F.
One thing people often miss about Tustin is the "Loma Ridge" effect. Because of our proximity to the Santa Ana Mountains, we can get those Foehn winds (Santa Anas) that dry everything out. Right now, the humidity is swinging wildly—from 24% today to a projected 67% by Friday.
What This Means for Your Week
Don't be fooled by the 78-degree sun today. By the time we hit next weekend, the daytime highs will have dropped by 15 degrees.
If you are a gardener, the low temperatures are staying very consistent. We are looking at a rock-solid floor of 52°F to 54°F every single night for the next ten days. No frost warnings, but definitely chilly enough to keep the heater clicking on in those older Tustin Ranch homes.
Actionable Next Steps:
Enjoy the sun through Tuesday, but dig out the umbrella and a heavier jacket for Thursday night and Saturday morning. If you're planning any outdoor projects, aim for the first half of the week before the humidity and rain chances climb toward 67%.