Therefore the mild air associated with the high pressure in the Pacific Northwest, was allowed to proceed downslope from the Rockies over a dry and relatively warm ground. Air moving downhill gets compressed, and since compression is a heating process, the air is warmed further. Usually in the Wintertime, cold storm systems constantly move southeastward from Canada, drawing Arctic air southward and knocking down the temperatures, especially across the eastern plains. As a result, the mild air does not get a chance to become entrenched long enough to produce record highs of this proportion. But in this case, the jet stream flowed unusually far north and east, keeping the cold air pinned into northern and eastern Canada, and allowing record breaking warmth to grab a firm hold on the Northern and Central Plains.
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