Arctic Air, Snow Returns to Rockies, Plains

April 22, 2013; 6:33 AM
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As April comes to an end and the United States surges deeper and deeper into spring, average temperatures in even the coldest spots will rise above the freezing mark. However, yet another surge of cold air into early this week will make winter coats a necessity across the northern Rockies and Plains states.

A strong dip in the jet stream will work in tandem with a cold front near the surface to send a pool of dry, arctic air across much of the western half of the country early in the week.

The air mass, originating from the Yukon and Northwest Territories in Canada, is arriving across Montana and North Dakota currently before pushing south into Colorado and Minnesota on Monday and as far south as northern Texas on Tuesday.

Within the heart of the cold air, mean temperatures will reach values of 20 degrees or more below seasonal averages. To put that into perspective, many locations from Great Falls, Mont., to Dodge City, Kan., will experience temperatures much more common of late January or early February than the end of April.

Precipitation will accompany the leading edge of the cold air, and several inches of snow are also likely to fall from Montana and Wyoming into tonight before expanding eastward into western portions of the Dakotas, Nebraska and northern Colorado on Monday and Tuesday.

Fortunately, storm total snow accumulations with this cold front are not expected to be as high as those of the most recent storm system which was responsible for close to a foot of snow from Cheyenne and Casper, Wyo., to areas just west of Denver, Colo.

The cold air will modify a bit on Wednesday and Thursday as the air mass expands south and east, but temperature departures greater than 10 degrees below normal will still be possible as far south as Lubbock, Texas, on Wednesday and as far east as Des Moines, Iowa, on Thursday as the cold front speeds towards the Great Lakes.

Winds aloft in the atmosphere will shift from the northwest to the west as the week progresses, allowing temperatures to moderate back to near average late-April warmth by the weekend.

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