It forms overnight as the ground cools the air above it ... in subzero temperatures. Cooler mountain air drains down into valleys in the evening, causing fog there as the night progresses.

Steady mountain snow will continue in Colorado's high country on Friday. Winter Storm Warnings and Winter Weather Advisories ...

To be clear, I do think that Cain Vineyard & Winery IS in fact the ultimate movie location in the Napa Valley, up above the fog line on Spring Mountain. But if I led this post with what I believe ...

High pressure overhead will continue to deliver mostly clear skies with a slight chance of overnight fog. High temperatures ...

While it can be beautiful to witness from above, valley fog can be very dangerous or near impossible to travel through. One moment you are driving through picturesque mountains, and the next you ...