Friday, January 3, 2014

"Arctic Vortex" To Blame For Our Intense Cold

Blame something called the Arctic vortex for the current bitter cold snap, the worsts to hit Vermont in a decade.
National Weather Service is forecasting
wind chills in the -30s today in northern Vermont.  

"Arctic Vortex" sounds like the name of a cheesy disaster movie, but it's actually a normal winter weather phenomenon.  The problem is, the vortex in the wrong place at the moment.

The vortex is a whirlpool of intensely cold air that almost always spins around somewhere in or near northern Canada every winter and lasts for months.

If the vortex is over north central or northeastern Canada, passing storms will often snag a chunk of frigid air from the vortex and send it crashing through New England.

Those are the standard issue one or two day spells of subzero mornings and bone chilling days we get all the time every winter.

What's different this time is the vortex has been temporarily pushed southward by higher than normal air pressure over and near Greenland. So the Arctic vortex is no longer in the Arctic, where it belongs.

It's close to us instead.

Specifically, it's been over Quebec the past couple of days. Temperatures fell to around 50 below in central Quebec Thursday morning.  That's about as cold as it's ever been in that part of Canada.

With the Arctic vortex so close to Vermont, it was bound to get very cold. And it did.

Making it worse was that storm that got going on the East Coast yesterday. For one thing, clouds from the storm blocked the feeble January sun, so the sunshine couldn't warm us up, even by a few degrees.

Worse, the storm set up a steady north wind that drew the coldest air from Quebec southward into New England during the day Thursday. That's why the temperature fell all morning and most of the afternoon yesterday, rather than rising during those hours as it normally does.

The abnormal cold affected how much snow fell in eastern New England with this storm. You've heard of lake effect snows, right? You know, in western New York where cold winds sweep over the Great Lakes, pick up moisture from the relatively warm water and drops it as heavy snow.

The same thing happened in eastern Massachusetts. Usually, there's not much contrast between the air and ocean temperature, which you need to get lake, or in this case ocean effect snows.

This time, east winds blew off the relatively warm water, hit the frigid air on the coast, and caused and "ocean effect" storm that dumped two feet of snow on some parts of Massachusetts.

The Arctic vortex is still nearby, so the subzero, painful cold will continue today into tonight. It will temporarily retreat to the north to make room for a storm system that will approach Sunday, bringing much warmer temperatures and mixed precipitation Sunday night and Monday.

The Arctic vortex will then sink south again,  but this time over the Great Lakes and upper Midwest. That means the worst of next week's cold will be there. Temperatures in that part of the country will be in record low territory, about 40 degrees below normal.

Here in northern New England, the fact the Arctic vortex will be a bit further west than it is now means we'll be on the edge of the bitter air.

It'll be below zero at night during Monday and Tuesday nights, and days will be quite chilly. But the intensity of the cold next week won't be as bad as it is now.

This really is an impressive cold wave for us. For the first time since 2004, Burlington will go two days without ever going above zero. Many places in northern Vermont will be in the 20s below zero tonight

It'll start to warm up Saturday, but at first you might not notice. Strengthening winds in the Champlain Valley will keep wind chills low.

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