Fog Season In Vermont Has Arrived And This Year Could Be A Doozy

Sunflower stalks on a foggy morning late last
fall in St. Albans. Vermont 

 Every year, in the final days of summer and the first half of autumn, dense morning fog is a frequent visitor in Vermont.  

The nights begin to get a little cooler. Meanwhile, lakes, ponds, rivers, even the soil is near its peak temperature of the year. 

These bodies of water, and the soil, and the leaves on the trees, emit moisture. When the temperature drops overnight, that moisture condenses into fog. It clings to the river valleys and can cut visibility to near zero until it burns off by mid morning. At least usually. 

The season has started already, as it often does in August. Patchy dense fog was scattered around Vermont early this Saturday morning. 

This autumn could well be an especially foggy one.  It was a much warmer than normal summer, last week notwithstanding, so water and soil temperatures are higher than they usually are. 

The increased contrast between the cooling nights and the warm water and soil is a recipe for fog.

Satellite view this morning shows fog in river 
valleys, especially the lower White and Connecticut
River valleys. 

You surely noticed this summer was also really, really wet. Soils moistures are high, so that adds a lot of water to the atmosphere. The more moisture available in the air, the more likely you're going to have fog.

Even in nights when humidity is low, the moisture coming from the ground, the rivers, the lakes, the leaves on the trees can really add plenty of ingredients for fog.

From now into October, any night that is at least sort of clear and calm will give us a bunch of fog. 

The morning fog in the autumn can be spectacularly beautiful. When foliage season hits, I always recommend people get an early start. The photographs of the fall foliage emerging into sunshine from the fog can be incredibly gorgeous. 

Of course, the autumn fogs can be dangerous. You're blasting down the road in clear air, and all of a sudden you punch into a fog bank. 

Visibility goes to zero, and you don't even see the car braking ahead of you, until it's too late. And yes, the fog can be dense enough so that you don't see the brake lights.  

Over the next few weeks, the sun is still strong enough that the fog will surely burn off by mid morning. The sun heats the air, the contrast between the cool air and the warm ground disappears, so blue sky and sunshine quickly re-appear by 10 a.m or so.

Dense fog cuts visibility to near zero on a 
St. Albans, Vermont street last year. 

Later in the autumn, the sun angle is lower, so the heat is not as strong. Especially this year, I imagine, we'll end up with several days that on paper should start out foggy then turn sunny. Instead, those days sometimes turn out to be entirely gloomy. The fog lingers, then maybe lifts into a low, gray overcast. The mountain tops end up in the sun, but us valley dwellers experience a dreary day. 

On some of those days, the sky finally clears late in the afternoon, only to fog up again that night. 

Fog can be beautiful, giving our surroundings a mysterious air. But much like in the winter, plan on leaving a few minutes early for work on calm mornings. Patches of fog will mean you'll need to drive more slowly.