Snow piles up... liquid water generally doesn't... snow (and ice/slush) can block/seal cockpit and deck drains, and dorade vents, and all sorts of things that don't leak during summer rainfall. Imagine a foot of wet/slushy snow in your cockpit... as the top layer melts (or rain falls on it) could it leak into your companionway? The slight bevel of my companionway slats is enough to keep running rainwater out, but not enough to be essentially submerged inches below a puddle and keep a water-tight seal... Audio speakers, ignition switches, throttle controls, and all sorts of other things in cockpits are generally good at fending off vertically-falling raindrops or splashes, but are no match for piling/drifting snow. Also keep in mind that When you get a foot of snow... the wind might move the snow around such that some spots have 1" and other spots have 2 or 3 feet... especially if your boat (as most sailboats are) is located in a flat/windy area... like near an ocean or lake. The office building window where I'm currently sitting nearly always has a view of snow "falling" up during storms due to the wind blowing across the building in various directions... but the rain in summer storms never falls up. I could easily imagine snow blowing in through dorade vents... between companionway slats... into cockpit lockers... etc... in ways rain never falls. If you had 50 gallons, I'd be pretty worried... 1 though? Nah... I wouldn't spend time hunting down that source.
