You may have read a dire-sounding warning in The Old Farmer's Almanac, "Beware the pogonip!" It shows up nearly every year in December. The expression "pogonip" is an anglification of the Shoshone word for cloud (payinappih). It names the atmospheric condition and effects of freezing winter fog, commonly formed in mountain valleys of the western United States, particularly Nevada. Apparently, the myth still persists that icy particles in the fog can be injurious to the lungs; this ironically in a state with a relatively high proportion of smokers.
Pogonip is not found exclusively in the western United States. Elsewhere, the phenomenon is known by the equally enigmatic moniker, "hoar frost." One can only hope that's spelled correctly and doesn't describe another kind of frigidity, though I would think the terms are mutually exclusive. The effect is the same; delicate tufts of ice, much like those found in a supermarket freezer tub, grow as a rime* on all exposed surfaces.
|A "pogonip" or hoar frost along the Nith River, in southern Ontario, December 2007.|
Though I haven't been back to my long-time residence of Nevada for more than 12 years, and these images are from Ontario and Minnesota, I still prefer the term pogonip. Some might call it magic, the silver lining to a cold land.