Flat tire during winter storage

went to check on my Boxster yesterday and discovered that one of the tires has gone flat. Unheated garage and it gets real cold here in Maine during the winter. pretty sure tire wasn't damaged in any way when I put it away. Anything to be concerned about or is this not uncommon in cold storage?

You have a slow leak. I've winter stored cars for the past 25 years plus and they always hold air.

I've found that if I lose any pressure over the winter, all 4 tires lose similar amount of air pressure (e.g. 3 lbs of air per tire). If you have only one tire losing air to the point of flatness, and the other three holding, but losing less, you have a leak in that one. Fill it with air, spray with soapy water all over the tire, and you should be able to see the leak. Could also be the tire valve stem.