Please understand that blanketing is a full time job. Throwing on the first blanket you find at the feed store&leaving it on all the time is like grabbing the first jacket in the closet &wearing it all the time, despite temp changes. I promise your horse would rather be nakey
I know these cold temps are scary, but a horse with an adequate coat can regulate their own temp. If you blanket with a medium/light fill you limit the horse to the temp of blanket. This is a big risk to their health!
Of course every horse is different and rain and wet snow can definitely be dangerous if the horse becomes soaked
If your horse is healthy @ has gone all winter without a blanket, keep it that way! I recommend making sure they have 24/7 GRASS hay in addition to whatever else they usually eat, warm water, shelter, and dry places to lay.
Most of our horses have access to the barn that’s bedded with straw, but the pastured horses have tree cover and large windbreaks with fresh straw put out each day. We check them all multiple times a day to ensure they are okay!