Skiers at Gore Mountain recently were treated to the sight of clouds filling the valleys below them as they reached the top of the lifts.
It was a particularly good example of a not-uncommon condition in this part of the country.
Nick Bassill, director of research and development at the University at Albany’s Center of Excellence in Weather & Climate Analytics, said clouds or mist packing in below hilltops and mountains can be an example of valley fog or the result of a temperature inversion.
Satellite views of upstate New York in the morning in late summer and early autumn often show fingers of fog extending through many valleys, he said.
Valley fog happens as the air close to the ground cools, particularly overnight, lowering the temperature closer to the dew point and causing the air to become saturated with moisture.
Temperature inversions happen when a stable mass of warm air sits above a mass of cold air and the wind is so calm that neither moves. This is a reversal or inversion of the normal warm-below, cool-above order.
All that stability traps moisture and creates low clouds that are strikingly beautiful to gaze down upon from a ski slope, but sometimes not so enjoyable to drive through.
Temperature inversions can also trap smoke and other pollutants at or near ground level, harming air quality and even creating public health threat in severe or extended situations.
More often, the wind picks up or the ground-level temperature rises, and the inversion ends.
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