Fog Notes for Henry, Ron, Ruth

Henry published an excellent video tutorial yesterday talking about Radiational Fog, something that the East is becoming familar with this time of year. I'll add to that by showing this Visible Satellite animation from yesterday morning showing radiational fog in the valleys of NW Pennslyvania and SW New York:

Now remember, a Visible Satellite is like a camera image high in the sky looking down on Earth. In this case, it's showing the fog in the valleys (mimicking the dips in the mountains). Unlike the clouds in the picture, fog doesn't move, but rather slowly disappears as the sun "burns off" or rather evaporates the fog, as Henry explains in his video.

Next up I want to showcase a beautiful picture by AccuWeather.com Weather Photo Gallery user Ruth Healy. This was taken near Calgary, Alberta, Canada.

And finally, some more explanation to go with Henry's explaination of Ron's "rolling fog" video from last month. You may recall the video, which was a timelapse of about 8 minutes of video:

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Henry explained in a video a few days later that this was not Radiational Fog, that we talked about above but rather Gust Front Fog, which he said was called by "mixing" of the cold and warm air. Ron's followup question was: If the air is "mixing" why does the fog appear to be "domed off"?

To clarify a litlte further, there are three types of fog:

1. Radiational Fog (temperature cools and fog forms)
2. Advection Fog (warm air moves over a cold surface and fog forms)
3. Mixing or Evaporational Fog (two air masses meet and air fogs)

What we mean by "mixing" was just that two different air masses formed the fog, as opposed to an airmass moving over water (Advection) or one airmass which is cooled itself (Radiational). While the air masses are mixing with each other, that point where they meet and the fog starts is a dome-like structure, not unlike the way that cold fronts are often depicted:

In fact, the gust front is a (small) type of cold front - cold air moving into warm air. Cold fronts look like the illustration above, but normally the differences in temperature and humidity aren't as stark as that day in the mountains, so you can't normally see it coming. But that cold air which comes from the top of the thunderstorm, hits the ground and spreads out, is so cold, and the air in Pennsylvania that day was so unusually warm and humid, that you got this effect.

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