Same here.I live in Wyoming and my horses stay out during snow storms, blizzards and cold as low as -25 F... I just make sure they have plenty of hay to eat and my water tanks are heated to give them plenty of water. They have loafing shed to go into, but I rarely see them in it, even in complete whiteouts. I realize your area doesn't see snow very often, but make sure they have stalls to go in if they want, lots of extra hay and plenty of "warm" up water to drink . You will probably be surprised and see them outside playing in it.
I did chuckle cause right now 38 degrees would be a heat wave for us.
Horses are alot hardier than alot of folks give them credit for.