Mild, Zonal US Pattern But Cold Is Building and Expanding Across Canada

Written by on November 30, 2012 in North and South America, United States of America with 0 Comments

The pattern is becoming very zonal across the country and that means mild air will dominate the Lower 48 for probably the next 7 days. However, while there will be a chance of record warmth, a system crossing the Northern Tier next week will pull down cold air out of Canada bringing chilly weather back to Montana, the Dakotas and eventually across the Great Lakes. The very cold front sliding east bring enhanced warming up through the Plains and Midwest, will also pull down cold air just on the other side of the border.

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Cold Air Is Building: -47 in Yukon, -27 in Ontario

The cold pool is building over Canada and I saw a large swath at or below 0F this morning with a 27 below zero F over central Ontario. Up in the Yukon, temperatures were widely under 40 below with at least 47 below at one spot not far from the Alaska border.

There has been an unusually fast expanse of Canadian snow pack which is helping build and intensify the cold air and while many will fret about the onset of a mild, zonal flow across the US, the cold air is really just on the other side of the barbed wire fence, not way up in the arctic. So, as we get systems riding the powerful west-east jet across the country, storm systems will not only draw abnormal warmth ahead of the cold front but cold, arctic air will get pulled down on the backside bringing snow.

Negative PNA Means No West Coast Ridge, No Prolonged Cold For US Yet

The PNA remains negative and that means the west coast ridge isn’t there. Without an amplified pattern, there is no ridge going north and no trough going south, so the cold remains intact over Canada but with the widespread snow cover, the cold air is intensifying. We will eventually get the PNA to go positive and with the stage being set, look out once the flip occurs. I think by week 2 of December, as the cold air continues to build, lobes of this will begin to drift south. A flip to a positive PNA which supports ridging up into Alaska, would be the snap needed for the motherlode to come south and this may well happen further down the road.

Major Flooding With Threat To Life & Property Around Truckee, CA Is Now Occurring

A large part of the reason for the very mild weather is that strong Pacific jet roaring into the West Coast and bringing the tremendous amounts of moisture in with it.

The massive 5+ days of constant heavy rains is taking it’s toll throughout Northern and central California. Reports are now filtering through various wires of major flooding now occurring around Truckee and other areas are likely to follow as 10 inches has fallen and incredibly, a further 10 inches may follow from now through Tuesday of next week, that’s totals of 20 inches. This event will likely be historic for rainfall and unfortunately, devastation is likely too.

Check out this amazing water vapor image (seen on twitter, by 28storm) showing the long fetch of deep tropical moisture extending unbroken from the central Pacific all the way to California.

 

A huge vortex between Alaska and Washington is rotating one low after the other into the Pacific Northwest, this is trapping the subtropical jet underneath and it is this, which is transporting deep moisture all the way from near Hawaii. The far reach and the lack of movement with the trough means those rains just keeping on piling onshore.

Below is the rain totals already recorded over parts of Northern California.

Courtesy of The Weather Channel

Unfortunately it looks like a further 10 inches of rain is highly possible for the same areas over the next 5 days with  heavy rains and strong winds continuing to pile onshore.

Snow levels are high as the air is mild. Snow is falling mainly above 7,000ft but above this level and right on the nose of this moisture rich flow, snows will pile up to between 5-10 FEET. Mount Shasta, elevated above 14,000 ft may see over 200 inches from this set up and this could rewrite the record books.

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