Temperature inversions to blame for negative temps, dense fog in the Yampa Valley
STEAMBOAT SPRINGS — Early risers woke up to chilly temperatures Monday morning. The National Weather Service in Grand Junction documented a morning low of -13 degrees Fahrenheit just before 6 a.m. Monday in Steamboat Springs.
The cold temperatures are due to recent temperature inversions, in which the air at the earth’s surface is colder than the air higher in the atmosphere.
Temperature inversions can impact air quality. To see current local air quality conditions and learn more about how air pollution can impact your health, visit http://www.co.routt.co.us/160/Air-Quality.
Inversions are common in river valleys, such as the Yampa Valley, according to local meteorologist Mike Weissbluth, who runs snowalarm.com.
“River basins tend to be good traps for cold air,” he said. “In the winter especially, there are other factors that help cold air pool near the surface.”
Fresh snowfall followed by a clear, dry evening contribute to inversions in multiple ways. Snow is efficient at radiating its temperature, so a clear, cold night can become even colder.
On a sunny, clear day, the snow reflects the sun’s heat instead of absorbing it. In winter, the sun’s rays are weaker — its low angle in the sky doesn’t heat up the earth as much as it does in the summer.
Cloud cover can also help break up an inversion. Weissbluth said clouds act as a thermal blanket over the ground, which “blocks the strong cooling from the snow surface.”
All of these contribute to persistent cold temperatures in the valley.
Cold air holds less moisture than warm air. As temperatures fall in the evenings, the air squeezes that moisture out into the dense, frozen fog that were seen in the Yampa Valley on Sunday evening. This also can create low-lying clouds at the top of the cold air dome, called a stratus layer. From the ground, this appears as a fog that hangs just above the earth.
“If you’re not actually driving through the cloud, if it’s not foggy — that’s a stratus cloud,” he said.
Dense #fog advisory in effect for the central Yampa River Basin until 11 am. This includes areas along Highway 40 from Elk Springs to Hayden. Dense fog has been reported at Hayden with webcams east of Elk Springs indicating dense fog as seen below @ColoradoDOT #COwx pic.twitter.com/RjtPUCbGoe
— NWS Grand Junction (@NWSGJT) January 14, 2019
Because inversions trap air in valleys, they can also create pockets of denser air pollution.
Routt County Environmental Health Director Scott Cowman said he believes recent inversions have contributed to a slightly higher level of pollution in the air, though air quality in the Yampa Valley is still very good.
An air quality monitor at the Routt County Courthouse measures the air and color codes the air quality based on how many particles 2.5 micrometers or larger are in the air.
“We’re seeing higher readings,” he said.
“This is sort of what we expected — that when we do have these inversions and we trap the pollutants, that number goes up,” he added. “It’s proving true to what we’ve expected.”
Weissbluth anticipates that a storm rolling in on Tuesday evening could provide cloud cover and insulation that could break up the cold temperatures.
“I don’t expect strong winds with the storm on Wednesday, but temperatures in the valley will certainly warm because they’re not going to get as cold at night,” he said.
A stronger storm is forecasted to hit at the end of the work week, and stronger winds will help “scour out” the inversion, he said.
“It physically mixes and forces those inversions to disappear,” he said.
It could also bring a few powder days — Weissbluth is calling for 6 to 12 inches of fresh snow from Thursday night through early Saturday.
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At 7 p.m. Thursday, the Yampa River’s temperature was 72 degrees at a spot in the Chuck Lewis Wildlife Area south of Steamboat. That’s about 15 degrees higher than the typical average.