During the evening hours of past Friday (June 26), strong-to-severe thunderstorms rumbled across the New York City area providing some heavy downpours, gusty winds and frequent lightning.

But that episode of storms turned out to be a secondary story to what happened after those storms passed…

Mammatus clouds formed on the back edge of severe thunderstorms on the tail end of an anvil of a cumulonimbus cloud. They created a strange and beautiful alien-like atmospheric landscape.

Residents and tourists alike on Friday evening looked up in the sky in awe of what they were seeing. A setting sun also made for beautiful sky imagery.

See other spectacular photos from over New York here.

What are mammatus clouds?

Previous Dr. Forbes blog entry: Mammatus clouds form when the updraft is very moist, and spreads out large quantities of ice crystals into the anvil.

As these ice crystals fall out of the base of the anvil, they begin to “evaporate.”

Technically the term for this process is “sublimate”, as they go from ice to vapor. This cools the air and creates small downdrafts.

These downdrafts create the downward bulges that characterize the mammatus clouds. Before long the ice crystals all sublimate.

At that point the air stops sinking and begins to rise back up in the clefts between those downward bulges.

Weather.com