Originally Posted by DancingArabian
You could try getting snow pads on your horse if it has shoes or getting hoof boots with studs.
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Snow pads worked well on my shod horses when I lived in Michigan, before I had access to an indoor arena. Lubing up the soles of the feet with oil (Pam cooking spray is easy to use, if it's not too cold to spray!) helps prevent snow from balling up in shod hooves, but avoid getting it on the shoe surface. I pulled shoes from any horse that didn't absolutely need them.
Lots of walking will at least keep your horse moving. He will probably lose some fitness, but IME it's not that hard to get back to where you were since you're not completely putting them out to pasture. Chances are there will be some less extreme weather days mixed in, so you may be able to add some trotting or light cantering in periodically. Master turns on the forehand or haunches. Work on your two-track and side-pass. Practice turning, stopping, backing, lowering head, adjusting speed/impulsion with leg and weight cues instead of reins. Get the perfect bend on a perfectly round circle in both directions. Periodically take a brief bareback ride just to get the muscles moving without losing daylight by tacking up.
Shady trails are good for less snow, but that could be dangerously dark after work. I'd stick to the arena (even riding around the outside of the fence line if the inside gets slushy or muddy) or any area you have enough light to feel safe. Wander around the property using your legs/weight to turn around anything you come to - a car, a tree, a wheelbarrow, a bucket, etc.
Allow your horse to adequately warm up to breathing in increased cold air volume from a good workout, and let him cool down completely in a draft free area before putting him back outside. Layer your clothing, layer your socks, regularly re-waterproof your boots, and always keep your ears & neck covered! Stock up on Walmart's 2/$1 knit gloves (or pay the $3 for pebble grip horsey ones) to layer under your good winter riding gloves. Have fun and good luck with the new job!