February for Vail. Other nearby places in the central mtns can be either Feb or March or even April depending on altitude and terrain you are looking for.
The signature back bowls have a lot of south facing terrain. By early to mid- March you become dependent on the storm cycle for good skiing back there vs mush or worse. Not to say March is horrible skiing at Vail - it is the official biggest snow month in Colorado - but if you happen to miss the storm cycle it can get interesting in the bowls. Roughly mid March through the first week of April is the big spring break period when it is usually more crowded.
Hard to say if the horrible early conditions will have scared off vacationers this particular year though... Vail is still only about half open, though at least back into the storm cycle so more is opening on a regular basis at the moment. This year I would still hold off till at least the end of February to let the snow pile up more for a better base.
I wouldn't worry about the cold. By the end of Feb it's already a lot less common than Dec or Jan for example.