Ask Storm Team 11: What causes fog?


Thursday’s Ask Storm Team 11 question comes from Sammy Abelseth. He asked: “What causes fog?”

There are at least a half dozen types of fog. Fog is basically water in the air!

We’ll highlight a few of the most common in our area:

Upslope fog occurs because of our mountainous terrain. Cold air in the valleys gets lifted allowing for the air to get even colder. The mountain slopes get an increase in moisture. As moisture rises, fog forms.

In the late fall and winter, radiation fog is most common. It’s when the daytime warmth escapes into space. On a clear night with light winds, if you get a thin layer of moisture near the ground underneath drier air, fog can develop as the moisture rises and air near the ground continues to cool. The air becomes super saturated.

We can also get precipitation fog as warm air moves in while it’s raining. A cooler ground allows the warmer raindrops to evaporate. However, there’s just enough of a saturated layer even after the rain ends to allow the development of fog.

Have a question for Storm Team 11? Click here to submit!

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