Freezing Fog Ices Vermont Trees Beautifully, Ices Roads Dangerously

Freezing fog this morning in St. Albans, Vermont
coated tree branches with delicate rime ice
A rare freezing fog advisory was in effect for the
Champlain Valley this morning. 

Freezing fog enveloped large parts of Vermont overnight, especially in the Champlain Valley. It left trees and pretty much everything else outside coated in ghostly white ice.   

And made things challenging on the roads. 

Freezing fog is when all the droplets in the fog are still liquid, even though the temperature is under 32 degrees.

As soon as these supercooled droplets as they're called  hit anything - a road, tree branches, your cold car windshield, they freeze.

On trees and other outdoor objects, the frozen water takes the form of rime ice, a delicate, feathery feature that is absolutely beautiful. 

On roadways, freezing fog forms virtually invisible black ice on pavement, especially on bridges and overpasses. 

The fact that in some cases only bridges are frozen, motorists are often taken by surprise. If they're going too fast, you can get some serious crashes. Especially if the freezing fog is thick and visibility is horrible, like it was in many areas in and near the Champlain Valley overnight and this morning. 

Freezing fog happens from time to time in Vermont. We had a bout of it around Christmastime last year.  When the sun hit those frosted trees, the scenery looked magical. It made the holiday season look that much better. 

Rime ice from freezing fog formed icy little 
needles on this St. Albans pine branch this morning, 

This morning's freezing fog was particularly dense in many spots. So dense that the the National Weather Service in South Burlington issued a freezing fog advisory for the entire Champlain Valley.

 It was the first time the Vermont NWS office issues such an advisory in a decade. 

The advisory stays in effect until 10 a.m today. If you're reading this early and planning on a drive, take it slow, keep your low beams on, and really be careful around those bridges and overpasses. And try to leave as much room as you can between you and the vehicle in front of you, 

The freezing fog should gradually lift during the course of the morning. At first it will probably transition to a low overcast. Eventually, the sun should break through for at least some of us.. 

It's tricky to determine when or if the sun will actually make an appearance. In warmer times of the year, the sun heats everything up enough to create updrafts that mix the air and evaporate the fog. 

This time of year the low angle of the sun means it can't heat things up enough to readily break up the fog. Some parts of the Champlain Valley could stay under the clouds all day. Or at least most of the day. 

Outside the Champlain Valley, there was much less fog, so other sections of Vermont will just have another partly sunny, cool November day. 

Tonight, the wind will begin to stir as a weather front begins to make an approach. Those winds should prevent another round of freezing fog from forming. Except maybe in the deeper valleys of eastern Vermont.