SEATTLE — Editor's note: The above video on noctilucent clouds over Lake Washington originally aired June 18, 2018.
Seattle saw "one of the most vivid displays " in recent years of the highest clouds in the Earth’s atmosphere early Friday morning, according to the National Weather Service.
Noctilucent clouds, or “night-shining” mesospheric clouds, are the highest clouds in the atmosphere, sitting at a height of 50 miles above the earth.
The National Weather Service Seattle tweeted the photos below just after 4:15 a.m. Friday and said, “What a way to start July!”
Noctilucent clouds form when water vapor and methane introduced into the upper atmosphere, by either natural events such as volcanic eruptions or manmade sources such as spacecraft, develop tiny ice nuclei within the extremely cold and dry environment at the edge of space, according to the National Weather Service.
The clouds are very thin and can only be seen during twilight hours due to the position of the sun. They occur most frequently during the summer months because global circulations in the middle of Earth's atmosphere transport water vapor and methane towards the polar regions.
According to the National Weather Service, noctilucent clouds were first observed in 1885 following the eruption of Krakatoa.
Sightings of the clouds are thought to be increasing due to a change in brightness and visibility due to human activity and climate change. Cloud sightings have also migrated south from their typical 50-degree to 70-degree latitude range.
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