How long can this stagnant weather go on?
Inland Northwest Weather Blog
By now, most of you may be getting tired of our boring, foggy weather. On the positive side, you haven't had to shovel any snow, and the roads have been in decent shape, except for some occasional icy spots from freezing drizzle. But the gray skies do tend to wear on some folks. Here's what it looks like from space.
The Columbia Basin is bordered by the Cascades to the west, the Selkirks to the north, the Panhandle mountains to the east, and the central-Oregon mountains to the south. A perfect bowl. Note in the above picture of the western US, the Central Valley of California also provides a nice elongated topographic bowl.
Second, you need moisture in order to form fog. And while we have been very dry, we still have had weather systems providing some moisture. Coupled with the cold nights, and you get fog and stratus to form. The Central Valley of California has been so dry this winter, they can't even produce fog!
The third ingredient is a lid to put on the bowl of fog, to prevent it from going anywhere. This is provided by the ridge of high pressure. High pressure results in sinking air. Sinking air warms. So while at the surface we're stuck in cold, sub-freezing temperatures, the air above us is much warmer. Locations in the mountains as high as 5000-6500'' have been reaching the mid-40s each day. The high pressure also keeps storms away from our area. Storms mean wind, and wind mixes the air which dissipates fog.