Basic UV coating means the protection is applied as a surface layer rather than being built into the lens material itself. The catch is that these coatings can wear down over time with scratching, cleaning, and general use — so the UV protection you start with may not be what you have midway through the season.
For a single weekend trip at lower elevations, basic UV coating will offer some protection, but it's still a gamble. UV radiation is 30-40% stronger at altitude, and snow reflects up to 80% of it back at you. That's a serious amount of exposure if your coating has started to degrade.
If you ski even a few days a year, it's worth spending a little more for UV400 (100% UVA/UVB) protection — it's built into the lens and won't fade over time. Think of it like sunscreen: basic coating is the equivalent of that old bottle sitting in your beach bag, while UV400 is fresh SPF 50 you can count on.