It looked like a scene from the Twilight Zone, or Stephen King’s horror story The Mist.
But the weird and persistent weather phenomenon that appeared Saturday morning in the Montezuma Valley is called “ice fog.”
The fog is formed when heavy humidity meets below-freezing temperatures. It occurs in mountain valleys relatively infrequently in the Lower 48.
The thick mist settled around Cortez and McElmo Canyon, topping out about 6,500 feet and stretching to the horizon. At higher elevations farther north, the weather was clear and sunny, offering a unique top-down view of the fog with Sleeping Ute Mountain piercing through like a floating island.
The fog caused flight delays and cancellations at Cortez Municipal Airport, according to staff with Great Lakes Aviation.
Airport manager Russ Machen said it could be the fog or recent unavailability of pilots that caused the disruption in service.
“It is common sense that you cannot land in it,” Machen said. “We need a certain amount of ceiling because we rely on a visual approach.”
Norv Larson, a meteorologist with the National Weather Service, said the ice fog was widespread, stretching from New Mexico, through southern Utah and into northern Arizona.
“It is kind of unusual for the Cortez area because you are not constrained by mountains,” he said. “It was caused by the prior storm leaving moisture in the air and then temperatures dropping.”
A quirk of physics, called supercooled liquid water, allows tiny droplets of water to remain liquid below freezing, Larson explained. When the droplets hit dust particles, they instantly freeze into ice crystals, creating the fog, also known as pogonip.
“A temperature inversion forms where there is warmer air above opposing the colder air below, forming a type of lid on the fog and creating a low stratus cloud,” Larson said.
Ice crystal attach to objects – or riming – giving trees their frosty appearance.
The fog is expected to break today as an arctic front creates a pressure gradient and winds that will weaken the inversion and mix the atmosphere.
