Monday, February 15, 2016
Temperature inversions in valleys
Yesterday was Valentine’s Day, which marks the typical end of the temperature inversion season in Boise and the Treasure Valley that began around Thanksgiving Day. As shown above, normally temperature decreases as altitude increases. An inversion occurs when it instead increases. There is an example with weather ballon data in an article from KOAA-TV in Colorado Springs titled Why the Haze?
Typically this microclimate results when cold air gets trapped in a valley due to calm conditions. Then fog can form, and pollution from auto exhaust and wood burning can build up. Eventually a change in weather accompanied by winds breaks up the inversion. But meanwhile we get depressingly monotonous cloudy gray days while the nearby mountains (like the Bogus Basin ski area and Idaho City) have clear blue skies.
You can watch an amusingly speeded-up five-minute YouTube video from 2014 showing an 8 mile drive up to Bogus Basin. The sun shows up at an altitude of 5000 feet versus the 2700 feet for the Idaho Capitol building downtown (that appeared at about 1-minute in).
Another five-minute YouTube video titled What you never knew about treasure valley inversions discusses how they occur. Another three-minute YouTube video from the National Weather Service office in Medford, Oregon on The Inversion uses graphics rather than just words to explain inversions. A third brief BBC Weather video on Temperature Inversion describes how in a valley it may be 0 C (32 F) while the air above is at 12 C (54 F).