Have you ever been driving down Hwy 395 on a cold and clear winter day and then suddenly hit a patch of dense fog by Lake Crowley or Mono Lake?  This fog is known as Poconip/Pogonip (deriving from a Shoshone word meaning “fog” or “cloud”), and while it is fairly common here in the Eastern Sierra, it is rare phenomenon outside of our region.

Poconip is a freezing fog that typically forms in low-lying valleys on cold and still nights.  The fog forms when an inversion traps cold air over a warm and moist surface like an unfrozen lake.  This meeting of warm and cold causes the moisture in the air to condense into water droplets that become supercooled due to the cold temperatures.

When these supercooled water droplets come in contact with a surface like a tree or fence line, they instantly freeze into rime ice.  Depending on how long the fog lasts, the rime ice can build into a thick layer and transform the landscape into a winter fairytale of ice.  When the fog burns off and the sun comes out, there’s a brief period of magical beauty with all the trees, sagebrush and fences glittering with ice.

Because Mono Lake is so alkaline, it doesn’t freeze. This makes the Mono Basin a perfect place to see poconip during the winter.  Long Valley also frequently sees poconip fog before Lake Crowley freezes over.

While beautiful, poconip fog can be dangerous.  If you’re driving and encounter it, visibility can drop dramatically and roads can be icy.  Be sure to slow down and give greater following distance to other cars on the road.  And remember that poconip forms when it’s very cold, so be prepared for cold wintery conditions if you go out looking for it.

Poconip truly is one of the most stunning winter phenomenons and we are so lucky to be somewhere it happens regularly.  It’s a reminder of how our dramatic landscapes, cold winters, and desert valleys work together to create something truly special.

Thank you to Don Chambers, Sierra Forever Board Chair, for the photos!