the last pass to be cleared for traffic won’t open until well into June.

 This is true of a bad winter in the Sierras. However, in Mt. Shasta I have seen winters so powerful that the road up to Panther Meadows and beyond never opens beyond Bunny Flat on Everitt Memorial highway which is the only road paved that high on Mt. Shasta that I presently know of.

For example, around 1992 there was 12 feet of snow in the town of Mt. Shasta and roofs were collapsing one by one from the snow load. This might have been when I skied on 40 feet of snow from Bunny Flat to 7 mile curve on Everitt Memorial highway too.

So, even though this hasn't happened since then it's important to know this can happen some years both in Mt. Shasta which is the lower part of the Cascades and also it can happen in the Sierras too with this much snow. This is why from November to May or June you always should be prepared if something like this happens to you in Mt. Shasta or the Sierras (if you want to survive being there).