Albert,

My limited experience is that in order for Oak Flats to be skiable, the required snow must all fall in one storm. That number (in inches) will vary depending on the density of the snowfall, but maybe 6" - 8" or more (with frozen ground). Oak Flats is low enough in elevation that it does not build up a base layer through the season - there is usually significant snow melt between storms.

When there is a good single-event storm, it is a delightful place to ski. Often someone local to that area will post notice if a storm has provided such a gift.

Dave