A few days ago Leah got up earlier than me — thanks, Mollie — and saw that most of the rest of the world had disappeared beneath a blanket of fog. She shot a bunch of pictures, and this is one.
The long ridge on the right is Mount Alto.
We often see spots of fog in the morning, here and there, mainly collecting in the lower parts of the up-and-down terrain below the mountain. This is called valley fog. It’s caused by radiative cooling of the air near the surface which then flows downhill into the valleys, where it collects. If it’s cold enough, water vapor condenses to form fog. So, it’s really a type of radiation fog.
This morning, however, the fog was everywhere, not just in the valleys.
This view is directly towards downtown Rome. The tower is a telephone company antenna.
I can’t see the top the City Clock, which stands on what used to be Neely Hill and is now called Clock Tower Hill, but it was just peeking through the fog. The stacks and cooling towers of Georgia Power’s coal-fired generating plant is barely visible on the horizon.
This fog is radiation fog. We had a cool, clear night with conditions just right for fog formation. We also sometimes see a sort of reverse advection fog. Advection fog is usually considered to be the type of fog that forms when warm, moist air moves over a cool surface, causing water vapor to condense and form fog. In our cases, however, it is cool air moving over the warm rivers, causing moisture evaporating from the river to condense as fog in the cool night air. This is usually called steam fog.
We often talk about fog “lifting” as the sun rises. As the sun rises, it tends to warm the ground, which causes the air just above to get warmer and the fog to evaporate. As the air gets warmer, the bottom layer of the fog retreats upwards until all the fog dissipates. If the fog is thick enough, it can keep the surface from warming because not enough sunlight can penetrate. People on the West Coast are probably more familiar with that kind of thick fog that we are here in the Southeast.
This was a welcome change for us. For a couple of weeks we, up here on the mountain, were the ones in the fog. For the people down below, we were up in the clouds.
How long can this kind of fog persist? Days?
Love seeing that low ground fog. We’ve been seeing radiation fog here as well. It’s really a lovely sight low in the cow pastures. Now I’m wondering if you have a good view east in the morning and if you can see the shadow of the earth and the Belt of Venus before sunrise there?
Paul — Around here, this kind of fog doesn’t last past morning. I think on the West Coast, fog can last all day.
Robin — We see the shadow of the earth and the belt of Venus on the opposite horizon from the sunrise or sunset, so here we see it when looking towards the east in the evening as the sun sets.