We've had a full week of thermal inversion here in Seattle, with sprinkles of sunshine, fog and frost. The freezing level has retreated to 11,000 feet, below the summit of 14,410 Mt. Rainier, except it is "on the deck" in the passes at 3,000 to 4,000 feet. We get great, thick pea soup fogs at night, that begin to freeze just before dawn. Morning driving is hazardous and our usual commute snarl has gotten much worse.
This phenomenon is called "rime." It doesn't happen only on this small scale -- summits of the Great Northwest westernmost Peaks, like volcanic Mt. Shasta, often are covered with rime ice from the moisture laden winds that come in from the Pacific and condense as they rise to go inland. When I climbed Shasta in 1996, the entire summit looked like a big, frozen cauliflower -- today, sadly, climate change has left Shasta mostly snow and ice free. This is true of all the great summits and glaciers I have known; they have become noticeably bare in just the last 10 years. Glaciers have retreated as ablation zones grow wider. Climbing routes now entail slogging through loose dirt, mud and stone before getting onto any proper mountaineering ground.