Temperature extremes have been pretty unusual across the United States so far in 2014. Looking back over this time period quickly reveals at least part of what was going on: the polar jet stream got into a serious rut.

Never in the historical record have such large areas of the country experienced such radically different temperature extremes as they have so far in 2014.

January 2014 was remarkably mild across nearly all of Alaska, resulting in this January ranking among the  “top ten” warmest on record for many Alaskan communities according to preliminary analyses.

October in Alaska this year was more like September, with warmth and rain in place of autumn chill and snow. Wind anomalies related to unusual pressure patterns conspired to bring a steady stream of warm, wet air from southerly latitudes into Alaska.

For much of Alaska, lack of snow, soaking rains, and record-warmth have made October feel more like September.

A heat wave struck the Midwest in late August and early September 2013. This map shows the hottest temperatures in the United States between August 1 and September 8, 2013, based on data from NOAA's Real-Time Mesoscale Analysis.

On July 30, 2013, a weather station on the southwest coast of Greenland preliminarily set a new record high temperature for the country, but whether it will stand as an "official" record after scientists apply quality control procedures isn't yet known. What is known? Greenland's getting warmer.

In late July and early August, unusually high temperatures dominated Europe, from the Mediterranean Sea northward to Scandinavia and the British Isles.This map shows temperature between July 16 and August 11, 2013, compared to the 1981-2010 average for the same time of year.