Friday, December 9, 2016

Dark December Made Darker With Persistent Clouds

The sun briefly broke through the clouds in Burlington
Vermont's intervale Thursday morning, creating this'
great lighting. But, as is typical this time of year,
the sun was snuffed out by the clouds within minutes. 
We all know the shortest days of the year are in December, near the winter solstice.

We also can see the darkness is made even worse by the fact it's usually very cloudy during the few hours the sun is actually above the horizon in December.

I guess this must be Dracula's favorite month.

There's reasons unique to the time of year that makes New England, and much of the rest of the Northeast and Great Lakes areas so cloudy.

Winter is of course stormier than the summer, so that adds clouds.

Another big factor is the fact that the Great Lakes, and most other bodies of water in southern Canada, the Midwest and Northeast haven't frozen yet.

Cold air blowing across these open bodies of water lift moisture from them, and they condense into clouds.

Downwind of the largest bodies of water, like the Great Lakes, this is the peak season for lake effect snows, too. The water is still relatively warm, the air is winter cold. The moisture picked up from the lakes in these situations can dump big snows lake effect snows.

We saw this yesterday, when western New York picked up as much as a foot and a half of snow, and a lake effect snow squall in Michigan caused a 30+ vehicle pileup that killed three people.

Another reason for the seasonal gloom is inversions. Dense, cold air often sinks into valleys at night. Slightly warmer air above forms a lid that traps moisture, resulting in a deck of drab overcast.

In the summer, the sun is strong enough to quickly break these inversions as its heat causes updrafts that break up the inversion, and the clouds.

In the winter, the sun is weak, and often not able to break up the inversions. So it stays cloudy. At least in the valleys. On these kinds of days, you might be in brilliant sunshine above the inversion on mountain peaks, while valley dwellers sulk under the gray overcast.

The good news/bad news for sun lovers is we're starting to get into the season of sharp blasts of Arctic air from Canada. These airmasses are quite dry, so the clouds often break up during these chilly spells.

But then, they are winter blasts, so it's hard to enjoy the rare treat of sunshine when it's below zero out.

Ah, winter.

1 comment:

  1. i think it gets way better once there is snow on the ground (working on a solid snowpack east of the greens!). even at night it isn't too bad with everything covered in snow. November (and snowless decembers like last year) are brutal.