Not sure how to say this, but if you assumed tires would hold air all winter, that's a really bad bad bad assumption.
If you go by the book, you really can't assume they'll hold air for a day. Ideally you check the tires at the initiation of every drive and at every fuel stop...
...and maybe that seems extreme and I know a lot of folks don't do the every trip/every fuel up, but seriously after anything more than a month or two, you really need an 'official' pressure reading and several visual inspections in between.