Wednesday, October 27, 2010


Steam fog over the Musconetcong River, New Jersey.

Being up at dawn for the last few months, and doing work that requires me to see things (bird surveys), has made me very aware of fog. In fact, I just realized now, after 3 decades, that fog is almost uniquely a creature of the fall.

Why? And why in the morning? And why over water?

For answers, I turned to my favorite source of erudite weather knowledge: USA Today. Actually, it was the first thing that came up in the search engine, but it gave good descriptions of the two main types of fog: steam fog and ground fog.

Steam fog forms over water when the water is warmer than the air (see above). This is the stuff that makes early morning ponds and rivers so picturesque this time of year.

Ground fog is more my nemesis, cloaking vast areas and killing precious visibility. It forms when the ground is colder than the air. It supposedly happens more in the fall because the nights are longer, allowing the ground more time to cool off. This must also be due to the shifting cold and warm fronts of air that happen in fall. (This in turn contributes to the windier weather this time of year...something I've also just noticed). Fog also seems to happen more in certain areas, which must be well known given that there are even highway signs that say "FOG AREA"! Mysteriously, large grasslands seem to be prime fog areas...when there is fog in the forecast, it can be completely clear on the drive to work, but the grassland is engulfed. It is pleasant to breathe in fog, by the way. But hard to see through.

A fog bow, somewhere in south Jersey...

Another great mystery of fog...the "Fog Bow." Just as it sounds, this is a rainbow-shaped thing made entirely out of colors, just a white tube of cloud. I never would have known, or believed, that they existed until I saw one a few years ago. Also on a big grassland in south Jersey. I googled "fog bow" because that was the only name that I could imagine it having. I was correct, apparently, but I still have no idea (or interest in, really) how it formed. I prefer to leave this mystical fog-beast a mystery.