WeatherWatcher: Noctilucent Clouds

Photo by Skunk Bay Weather (Greg Johnson)

Noctilucent clouds. What used to be a rare sighting has been quite common the past two years during summer months. This July they have been almost a daily occurrence on clear nights. Greg Johnson,  who does the Skunk Bay weather station with web cameras and the Skunk Bay Weather Blog, explains them in detail here.

In short, Noctilucent clouds are only visible during astronomical twilight and about 2-3 weeks on either side of the summer solstice, towards the northern horizon. Astronomical twilight occurs between about 10:43pm to 12:06am and again starting about 2:21am to 4:38am for those who might try to photograph the phenomenon.

The clouds occur very high up in the atmosphere, catching sunlight from beyond the horizon, which is what makes them visible at night. Normal clouds exist from sea level to as high as 50,000 feet or so. Noctilucent clouds occur around 250,000 feet to 280,000 feet, which is about 47 - 53 miles up.

The clouds are generally only visible near the summer solstice due to the angle of the sun over the northern horizon. During summer months the north pole is pointed slightly towards the sun, allowing light to make it past the horizon at these higher altitudes during astronomical twilight.

Noctilucent clouds are formed by tiny ice crystals around 100nm or less in size. The cause of the clouds is somewhat unknown. Theories are that it is particulate matter from volcanic activity, space dust, water vapor from space dust or passing comets, to a combination of all of the above. Space bound rockets seem to have a connection with creating these clouds as well. Some even point to a connection with anthropogenic global warming.

No one really knows yet what is causing these clouds, or the sudden common occurrence of these clouds. I will note the first recorded observation of Noctilucent clouds was in 1885, two years after the 1883 massive eruption of Krakatoa, which sent the world into a mini glaciation period (ice age).

The National Weather Service in Seattle has also been catching these clouds on a daily basis lately. Here's this morning's twitter post and photo from the Seattle National Weather Service office located on Sand Point.

It's another noctilucent cloud kind of morning at NWS Seattle. This is starting to feel like a daily twilight occurrence. #wawx pic.twitter.com/Tm1FzqlOME

— NWS Seattle (@NWSSeattle) July 12, 2018

For those curious about Skunk Bay Weather, you can follow the links above and in this sentence.  Skunk Bay Weather is located on the northern tip of the Kitsap Peninsula in Hansville, Washington. Greg Johnson runs three primary web cameras pointed North Northwest, North Northeast, and Northeast. He stitches the three images together to make the panoramic view images such as the one I've included at the top of this article.

He also runs a weather station and has a very well built website with a lot of local northwest weather links. Much like me, he also archives and shares his weather data for future research, including a shore side thermometer and a second thermometer located inland which is protected from marine air influences.

www.shorelineweather.com