Steve C. asked me to post my before and after pictures from this weekend (Saturday), when I was in the Tioga Pass area. These pictures were taken just above Spuller Lake, looking across the Hall Nature Area toward Mt. Conness, elevation maybe 10,500 feet. It got worse then this, but a totally grey picture is not so interesting to look at it.
Before
After
This change in conditions happened in less than 10 minutes (though I had already encountered hail about 30 minutes earlier, and the clouds had been ... interesting). I took some video too, but posting that is beyond my capabilities.