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The Pattern That Keeps on Giving

May 8, 2013; 9:54 AM ET

Wednesday, 11:40 a.m.

We've started to see some more consistent signs of spring across the country in the past week or so. It has been quite warm over the Northwest, with Seattle setting a record on Monday by reaching 87. The warmth has prevailed up into neighboring British Columbia, as evidenced by the highs from Tuesday:

Even in the northern Rockies and northern Plains and up into southern sections of Saskatchewan and Manitoba, it was warm Tuesday:

And, of course, the interior mid-Atlantic and especially interior New England up into Quebec has been enjoying a nice run of warmth in recent days with an upper-level ridge of high pressure in place.

Furthermore, the upper-level low now rolling across Virginia is producing showers and some thunderstorms, not snow for a change. Similarly, the upper-level low over the interior West is mainly a rain producer, particularly along the Front Range, where it snowed less than a week ago.

Despite all of this, we're not yet done with these chilly invasions from the north. Beyond the upper-level low over the mid-Atlantic, a couple of cold fronts will come charging through the flow, the second of which will pull a much colder air mass back down the Plains to the Gulf Coast and into the East.

Where is it all coming from? North Canada and Alaska. There's still plenty of snow on the ground in the high latitudes of North America:

Those numbers are in centimeters, of course, but it illustrates the fact that it's still cold across much of Northern Canada, as well as in Alaska. In fact, the numbers in Fairbanks are nothing short of extraordinary. The period from April 3 through May 7 was the coldest ever on record, with records dating back 109 years. During that stretch, temperatures have AVERAGED over 15 degrees below normal. And in Fairbanks, they STILL have a foot of snow on the ground, a snow cover that has been continuous since October 15! Even in Anchorage, the snow only melted off this past weekend.

All you need is some semblance of blocking, and it's not hard to pull a piece of that cold air still in place up across Canada and Alaska and bring it into and through the pattern, despite the recent run of warmth with the retreated jet stream across the northern tier of states. And right on cue, look at the GFS anomalies for Friday evening:

The upper-level ridge over the Northwest Atlantic will offer up enough resistance to force that disturbance heading toward Minnesota to dig southeastward, bringing a chunk of cold air along for the ride. The front ahead of it will be relatively weak, though Friday will be a cool day across the Midwest and Great Lakes in comparison to recent days as well as to normal:

The air mass behind the second front is much colder. Look at the same chart for Sunday:

So, just when you thought it was safe to put everything in the garden and put away the jackets, it's going to turn cold again, with the danger of a freeze into the Midwest and Ohio Valley Sunday night, and into the interior Northeast Monday night. Frost is likely in much of the region, especially where it is clear and calm, and that could extend into the Roanoke Valley and maybe the Tennessee Valley.

It's the pattern that keeps on giving, and we can thank northern Canada and Alaska for helping to deliver another cold blast to the country this weekend into early next week.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Joe Lundberg
Joe Lundberg, a veteran AccuWeather.com forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.