The jet stream pattern that brought flooding rains and heavy snows to the Pacific Northwest for the past two weeks isolated a dome of high pressure over Alaska. Sitting in the perpetual darkness of the northern winter and cut off from any southerly winds, this pocket of air became increasingly cold, with regional temperatures down to 40-50 degrees (F) below zero.
Now, the jet stream has shifted, pushing a ridge of high pressure up from the south and nudging the frigid, Alaskan dome to the east; as a trough develops on the east side of the ridge, this extremely cold air will plunge toward the southeast, bringing the lowest temperatures of the season to the Northern Plains and Upper Midwest. Moderating as it pushes southward, the cold front will produce dramatic cooling over almost all of the eastern U.S., including northern Florida.
Such events remind us that weather patterns in our atmosphere, governed by the jet streams, are rarely stable. Ridges form and break down; troughs plunge and then retreat. This week, Alaska's recovery is at the expense of eastern North America.
