On Sunday morning, the National Weather Service office in Great Falls, Montana, caught not rain or birds on the radar, but a phenomenon called “gravity waves.”
In an ocean of air above us, gravity waves are akin to ripples on the surface of a calm lake or pond when you throw a stone into the water, according to AccuWeather Meteorologist Reneé Duff.
“In the atmosphere, the 'stone' disrupting otherwise calm or stable conditions can be a severe thunderstorm, winds blowing over high terrain or fronts,” Duff said.” All of these weather phenomena force air upward that would not be displaced otherwise. As this air is pushed upward, it wants to sink back down in order to remain in a state of equilibrium. It may take many up and down waves for this state to be reached.”
Duff explains that, more simply put, they are the waves generated when air is displaced from a balanced or calm state.
Gravity waves in the atmosphere are visible through clouds, which showcase a ripple-like pattern in the sky. The clouds from gravity waves form at the upper crest of the wave, revealing this otherwise invisible phenomenon.
“When the weather is very quiet, the radar will switch into 'clear air mode,' which basically makes it much more sensitive to picking up smaller targets, such as cloud droplets,” AccuWeather Meteorologist Jake Sojda said. “The gravity waves create lines of clouds, which then show up as lines of higher reflectivity on the radar when it's in this sensitive mode.”
Like ripples in the water, these waves are the results of a disturbance, and they don”t have an effect on the weather people will experience, according to Duff.
“People can only feel gravity waves if an airplane happens to fly through them, which would result in severe turbulence,” Duff said. “If there is not enough moisture in the air for clouds to form, gravity waves can go unnoticed by the naked eye.”