BOISE, Idaho — Thick fog has settled into the Treasure Valley, bringing reduced visibility, icy roads, and colder-than-usual temperatures to the area— all thanks to a weather phenomenon called inversion.
- An inversion traps cold air in the valley while warmer air sits aloft in the mountains. This dynamic creates favorable conditions for dense fog to develop on the valley floor.
- However, those who venture into the mountains can escape the gloom, enjoying the sunshine and clearer skies above the fog layer in the valley.
- Submit your inversion photos here!
(The following is a transcription of the full broadcast story.)
A thick fog has settled into the Treasure Valley and while the fog is more dense west of Meridian, most areas are experiencing some form of reduced visibility and colder-than-usual temperatures.
This is all thanks to a weather phenomenon called an inversion, when cold air settles in lower elevations and actually gets warmer as you go up.
“Normally, when you think of going to the mountains, you think it’s going to be colder up there than it is in the valley. But when you have an inversion, it’s actually going to be warmer up in the mountains and colder down in the valley,” said National Weather Service Meteorologist Spencer Tangen.
The effects of an inversion go beyond just chilly mornings. According to Tangen, dense fog forms when temperatures and dew points meet, creating slick roads and even the risk of black ice.
“When we’re in an inversion, you can see dense fog, and so that’s going to reduce visibility when you’re driving. It can also trap pollutants near the ground, so a lot of times we can see air quality start to deteriorate because the pollutants don’t have anywhere to go,” Tangen explained.
But there is a silver lining—if you’re willing to climb for it.
I drove up to Bogus Basin, where the inversion’s ceiling ended. Above the fog, the sun shone brightly, offering a striking view of the clouds and valley below.
“You know, it’s actually pretty good if you’re up in the mountains. If you’re heading out to go skiing and you want to get out of the clouds, it’s usually very sunny during an inversion,” Tangen added.
