Two Rare Cloud Features Appear Over New Hampshire’s Mount Washington – Smithsonian.com

Mount Washington, the tallest peak in New Hampshires White Mountains, has long been the site of unusual and extreme weather. On Monday, its mountaintop observatory shared a striking view: not one, but two rare cloud features hovering side by side, lit by the sunrise.

The photograph, taken around 7 a.m., features a smooth, round lenticular cloud that swoops into a curled Kelvin-Helmholtz wave. The pair was likely a fleeting feature in the morning sky, as clouds like these are unstable and usually lasts less than a minute.

Seeing either type of cloud is unusual, meteorologist Matthew Cappucci writes for the Washington Post. But for both features to be wrapped up in one cloud? An exotic sight and then some.

As Cappucci explains, lenticular clouds are common around mountains that force incoming air to rise. If that air is carrying water vapor, then when it rises through the atmosphere and its temperature drops, the water will condense into a crowd of water droplets, the same way that droplets cover a cold glass on a warm, humid day. In the sky, the massive collection of suspended droplets forms a lenticular cloud, which erodes as the air sinks back down.

A single lenticular cloud recently appeared downwind of Californias Mount Shasta, per the Post. But Mount Washingtons cloud had another trick to share. Unstable conditions in the atmosphere can lead air currents to rise, while fast, low-density wind sweeps along the top. These wind currents can sculpt a cloud into the curlicue shape of a Kelvin-Helmholtz wave, meteorologist Jesse Ferrell tells AccuWeathers Lauren Fox.

Kelvin-Helmholtz waves normally appear in a repetitive series, making Mount Washingtons one-off wave unique. Then, the waves usually only last for a matter of seconds. A series of clear Kelvin-Helmholtz waves in Virginia was photographed last June when it appeared for less than a minute, according to the photographer Amy Hunter. The waves are named for the scientists that discovered the weather patterns that cause them: Hermann von Helmholtz and William Thomson, also known as Lord Kelvin, meteorologist Brett Rossio told Ashley Williams at AccuWeather last year.

Mount Washington is no stranger to mind-boggling winds. For 62 years, the Mount Washington Observatory held the record for the fastest gust of wind recorded on Earths surface. At 231 miles per hour, the measurement taken in April 1934 is still the fastest surface windspeed observed directly by humankind. An autonomous instrument recorded the current windspeed record, 251 mph, in 1996 during Typhoon Olivia in Australia.

The observatory is staffed year-round by scientists and staff, and has a history of hosting cats, like Elmer, Manx, Oomph and a litter of kittens who huddled by the coal stove the winter that the record windspeed was recorded. This Monday, temperatures at the observatory were in the low 20s, and winds gusted near 50 miles per hour.

The Mount Washington Observatory regularly shares sunrises and sunsets on social media. On a foggy day, visibility is severely limited in all directions. But on a clear day, viewers from the 6,288-foot-tall mountains peak can see the peaks of Mounts Adams, Jefferson and Madison of the Presidential Range.

Mondays view was special because, as the observatory said in its original post, "Mother Nature waved back."

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Two Rare Cloud Features Appear Over New Hampshire's Mount Washington - Smithsonian.com

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