Guarantee it has nothing to do with rain, snow, or coolant.
Rather, your AC system drain is clogged up. There is a hose on the passenger side firewall on the underhood side(or is SUPPOSED to be a hose, more like a 90 degree elbow). It can EASILY clog or fall off. When this happens, the water won't drain, it backs up, and it drains the only place it can....into the car.
Been there, done that, dry now
And before you say "But it's winter, I'm freezing my keister off and DEFINITELY not running my AC right now!"......remember that using your defroster also runs the AC compressor.
While you are at it, do the "hose" fix that is outlined on Rob Cheek's website. Costs all of under $1, and can help prevent this from recurring.
Ed Runnion -- Santa Clara CA -- 96 BBB, Many Mods
ROD, HAIL, SoCalSS, ISSCA, NAISSO