This is a wonderful time of year — unless you hate inversions.
From late fall to mid-winter, the Treasure Valley is often socked in by a foggy-smoggy mix of air that prevents us from seeing the big ball of fire in the sky.
That nasty air is a byproduct of inversion conditions, which is when cold air gets trapped on the Valley floor below warmer air. Moisture that’s caught in the cold air layer causes the fog we’ve been seeing this week, National Weather Service meteorologist Elizabeth Padian said.
Some years are worse than others.
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An inversion set up in the Valley last weekend, and forecasters don’t see much that will change the pattern. The low Friday morning will be 21, and the forecast high is 33.
“There’s nothing coming in that’s going to mix thing out. This pattern will exist at least the next several days,” Padian said.
A yellow air quality alert was issued for Saturday through Monday by the Idaho Department of Environmental Quality. Outdoor burning is prohibited in all cities in Ada and Canyon counties, as well as unincorporated Ada County.
Inversions can occur any time of year in the Valley but they are longer-lasting and more noticeable in the fall and winter.
Winter “inversion season,” if you will, typically runs from about Thanksgiving to Valentine’s Day, according to meteorologist Jay Breidenbach at the National Weather Service.
Those beautiful mountains around us help hold inversion conditions in place.
Inversion fog often dissipates by late morning or midday — but there are periods when we’re socked in for days or even weeks. Unsettled conditions are what you should hope for, anything that can mix up the air and push pollutants out.