Patchy Fog Anyone?

Patchy Fog Anyone?
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Weather Talk

POSTED: Thursday, April 24, 2014 - 12:15am

UPDATED: Thursday, April 24, 2014 - 12:16am

Have you ever wondered why the RGV gets very little fog on a cloudy night and quite a bit of fog on a clear night?

Fog will form when the ambient temperature (science fancy word for temperature) cools down and meets the dew point temperature.  What is the dew point temperature?  It is the temperature at which, at a constant pressure, the invisible water vapor condenses back into liquid water. 

On a cloudy night, the clouds often keep the Valley from cooling down too much.  If the temperature (say, 71) is above the dew point temperature (say, 67), then fog will not form.

On a mostly fair night, like Wednesday night, temperatures will keep on dropping down to the dew point because the heat radiates out into space.  Once that temperature gets near the dew point... presto... little water droplets form a cloud at the surface... or fog.

So sound the fog horn and stay close to the lighthouse.

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