>Big storms and up and down temperatures of maritime origin

Written by on October 29, 2009 in Rest of Europe with 0 Comments

> Dunnet Head, mainland Scotland and Britain’s northernmost point

A strong front is sweeping west to east across the USA right now ahead of a deep low centered over the Rockies that will bring 2-4 feet of snow to the mountains of Colorado, Wyoming, Montana, Idaho, and the snow bands will drop onto the western high plains as the cold air sweeps down the Front Range. Ahead of the front, warm air pours up from the tropics bringing mild and unseasonably warm weather but things will change dramatically across Kansas, Nebraska and the Dakotas as this trough migrates eastbound. This dynamic atmosphere with lots of key ingredients merging, my big concern is a large severe weather outbreak that could bring a dozen or more tornadoes. Meanwhile it’s all about the snow and blizzard potential for the Plains states.

Despite the colder influx of air out of Canada, if you notice, this air is NOWHERE NEAR as cold as it’s much stronger predecisor back in the first week to 10 days of October. The reason being, the cold air is of maritime polar, not polar or Arctic, i.e. it’s from the North Pacific or air that’s cooled over Canada with time of year and lack of daylight now. The air earlier in the month was purely Arctic and that air was driven south on board a highly amplified jet stream that roared straight from the polar region. That strong jet, picked up that air that has formed over the pole and drove it with gusto south into the base of the strong trough over the Northern and Central Rockies.

The cold now residing the Western US is Pacific origin and the air that is controling the US is both Pacific and Gulf oriented, behind the front Pacific and ahead of the front Gulf!

Don’t be fooled by the chilly air. Even the typical cold nooks of the high plateau valleys that collect cold dense air down their mountain walls at night at fall below zero that it’s Arctic, this is because it’s very cold aloft and under clear spots behind the storm center, winds lighten and the cold air aloft can drop down to the surface at night, especially with lots of snow cover.

High elevation gently sloped valleys can cool dramatically under clear skies, light winds and snow cover, it doesn’t need to be Arctic to see 5 to 10 below zero.

What’s this got to do with anything?
The pattern now wrapping itself around the Northern Hemisphere appears (to me) to be zonal and a positively driven North Atlantic Oscillation with as trough over the Greeland which will build severe cold over the high-elevated ice cap of the interior but twin ridges either side is a cclassic sign of a positive NAO as warmth spreads north into New England on the western side and north into Great Britain on the eastern side with of course the trough or cold pool over Greenland and the North Atlantic.

This is allowing the unseasonably warm weather northward from Spain and the Canaries up to northern Scotland where highs were topping the low to mid-60s. The heart of England was touching the mid-60s with the warm spot yesterday topping 67 degrees or 19C..

Because of low cloud covering most of the UK, nights are warm feeling with lows across the board very uniform and ranging between 50 and 55 degrees, unusal for the last days of October, but a warm, southerly flow allows this to happen when we see a set up like this.

The positive AO is holding all the cold, Arctic air over the North Pole and this allows the warmer air masses to push further north than what would otherwise be expected, throw in a postitive NAO and the warmth pushed north can be enhanced, the stronger the trough that drops over Greenland, often the stronger the warm surge is over eastern North America and western Europe!

A major storm is now effecting the western to central areas of the USA, behind the storm system as it pushes eastward, warm, maritime air will keep the atmosphere across the US map very mild for now.

As for the eastern side of the Atlantic, A major Atlantic low is set to hit us here in Britain within the next 24 hours bringing very heavy rain and strong winds. The storm will bring us more mild air and perhaps a cooler air mass as the system departs east of us and pulls cooler air out of the north, but as the set up continues with stormy, unsettled conditions, we shall remain mild, for at least the forseeable furture anyway.

Thanks for reading.

-Mark

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