[Sight of the Day] Foggy Morning Commute


Wednesday, September 21, 2011 (Germantown TN)—The autumnal equinox is still two days away, but fall weather is slipping in.

Nights have been cooler. We’ve had a drizzly day or two recently. And this morning we had thick ground fog, just perfect for a focused morning commute.

Sure, you have to be extra watchful and doubly defensive when riding in the fog, but there’s something about it that feels like riding in a dream.

A ride (or walk) in fog the is always mentally stimulating for me, and gets my creative juices flowing.

And that’s a good way to start the day!

Autumn ground fog conditions

Weather conditions needed to form ground fog are most common in the autumn. You basically need wet (humid) air, warm ground, and a cool clear night.

We’ve had the perfect conditions that past few days. A rainy Monday put a lot of water on the ground. A warm and sunny Tuesday allowed the air to become saturated with humidity, and the ground, still warm from summer, kept the dewpoint high.

A clear Tuesday night allowed the air to cool, causing the humidity to condense into Wednesday morning fog.

You generally don’t see fog in the summer, when night air doesn’t cool off enough to cause fog to form. In the spring, the ground is still cold from winter, so it’s harder to get ground fog to form. In the winter, fog is generally associated with a totally different set of weather conditions (such as warm, humid air pushing in over colder air).

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