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| Clear skies started this Saturday morning as barometric pressure in Vermont approached near record highs for December. Very high pressure almost always leads to clear skies. |
That is wicked high and it's still rising. Today, we'll come within a whisker of breaking the record for highest December air pressure in Vermont on record. It'll all just short of the records set around Christmas, 1949.
As I mentioned in passing yesterday, this won't screw up your life. Which is a good thing. There's enough high pressure trying to get ready for the holiday, without the atmosphere making it worse.
To oversimplify, when the air pressure is high, you basically have a big pile of air sitting on top of you. Air is sinking under areas of high pressure, which is how you get those elevated pressures to start with.
CLEAR, COLD
Sinking air also tends to destroy clouds, so it's usually pretty clear under strong high pressure systems. That this one is hitting in December is great for those of you affected by seasonal affective disorder.
The days this time of year are short to begin with. It's also almost always overcast in Vermont during December. So a spell of sunshine is always welcome this time of year, even if it is rather chilly.
If you're going to have near record high pressure, chances are it will happen in the winter. Weather systems - be they storms or areas of high pressure - tend to be stronger in the cold seasons than in the summer.
It's usually cold when the air pressure is super high in the winter. Sometimes super cold, if the high pressure came down from the Arctic Cold air is dense, which increases air pressure.
This time, and during the December record high pressure in 1949, the cold isn't extreme. The air did not come from the Arctic, but instead has some influence from the Pacific Ocean.
Today will only be slightly cooler than average. But strong high pressure encourages calm, clear nights.
Where it cleared up overnight in southern Vermont, temperatures at dawn today were in the single digits in places like Bennington and Springfield. Lingering clouds kept northern areas somewhat warmer.
Tonight will be by far the chilliest of the winter so far. Blame that strong high pressure. The Banana Belt Champlain Valley should end up in the single numbers above zero. The coldest hollows of the Adirondacks will be in the low teens below zero. Much of Vermont will be near zero.
That's not extreme for this time of year, but it is much colder than we're used to.
EXTREME WEATHER
I've noticed the weather can often get pretty extreme before and especially after bouts of near record high pressure, but that doesn't seem to be the case this time.
Sure, next week will be unsettled, but nothing wild for December.
In the 1949 high pressure, it was chilly during the peak of it, but record high temperatures preceded and followed the event.
Near record high pressure hit on February 12-13, 1981, and that brought seasonable cold temperatures. But right after that, Vermont had an extreme week long February heat wave, in which daily high temperatures were in the 50s to low 60s.
The wildest case of dramatic weather happening around the time of record high pressure was in 1920. this happening might have been 1920.
The all-time record high pressure in Burlington, Vermont for any time of year was 31.12 inches on January 31, 1920. This one came down from the Arctic, and it was bitterly cold. The high temperature that day in Burlington was minus 9 with a low of 28 below, still a tie for the third coldest reading on record in the city.
Then came an incredibly temperature surge. Enosburg Falls went from 39 below on the morning of February 1, 1920 to 47 above on February 2, a jump of 86 degrees!
The current high pressure will move on to the east and weaken starting tomorrow, opening the door to some fairly unremarkable storm systems to give us bits of rain and snow occasionally next week.
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