A magnificent fleet of lens-shaped clouds, known as lenticulars, gathered over the Blue Ridge Mountains Monday afternoon, an unusual event in the Mid-Atlantic region.  More commonly seen perched above the high peaks in the West, these clouds provided quite the spectacle for skywatchers in the Virginia piedmont and Shenandoah Valley.

Lenticular clouds are sometimes mistaken for UFOs since they resemble flying saucers.  Here’s a quick overview of how they form (from a previous CWG blog post on “weird clouds”):

When stable, moist air streams over a mountain and is heated,  it condenses into this lens-shaped cloud.
The wind that brings the air over the mountain then cools and sinks in a wave pattern, which can lead to a line of lenticular clouds extending away from the mountain that build on the crests of the airwave and diminish at the troughs.
These clouds can also stack vertically when there is a layer of dry air between two layers of moist air moving in the same direction over a mountain.

Interestingly, the last confirmed cases of lenticular clouds in the general region occurred almost exactly one year ago on March 10, 2014, when they were seen looming above the higher terrain west of Charlottesville.

The weather patterns were more or less identical. Mild air was streaming into the region from the west ahead of a cold front in the Northern Plains. As this air oozed over the crest of the mountains and condensed, the cloud-building process commenced.

Here are several more terrific views of the clouds from Monday shared with us via social media: