For most skiers, a DWR-coated pack hits the sweet spot. DWR (Durable Water Repellent) is a chemical treatment that makes water bead up and roll off the fabric, so your gear stays dry through normal snow exposure—think powder spray, light snowfall, and the occasional set-down in wet snow.
The catch is that DWR isn't truly waterproof. In prolonged wet snow or heavy rain, moisture will eventually work through the fabric and seams. If you're doing multi-day tours in coastal ranges where wet snow is common, you may want to step up to sealed-seam construction or a pack with an integrated rain cover.
One important tip: regardless of DWR coating, always stash electronics and extra layers in dry bags inside your pack. Think of DWR as your first line of defense—it handles the vast majority of ski days just fine, but a dry bag is cheap insurance for the stuff that really can't get wet.