One of the hallmark features of this past 2017–18 winter was a dramatic, out-of-bounds warm spell in the far northern latitude regions.
Here’s what happened: In late-February 2018, the closest weather station to the North Pole recorded temperatures that climbed 45ºF above normal. Researchers marveled at this level of departure.
Dramatic temperature anomalies can strike anywhere on earth in any season, but 2018 was the third consecutive year for anomalously warm temperatures over the Arctic Ocean. At the Arctic weather station, temperatures actually were above freezing for 2½ days during February.
Here’s some perspective on what this big Arctic temperature spike would mean to some locations in the continental U.S. At the end of February, the normal daytime maximum temperature in Washington, D.C., Denver, Colorado, Boise, Idaho, and Louisville, Kentucky is roughly 50ºF. Imagine all those cities sweating through 95ºF temperatures before March. Here are other examples: Chicago’s average February 28 high is 40ºF. That would soar to 85ºF with the Arctic 45-degree jump added. Des Moines, 41ºF average, would be 86ºF. Bismarck, at 33ºF average, would jump to almost 78ºF. Omaha, 45ºF average, would hit 90ºF.
Of course, not everywhere in the Arctic was warm in late February. Parts of Alaska, Canada, Greenland and the Arctic Ocean were unusually cold. One of the byproducts of that northern warmth was probably some influence on the colder start to spring, with the northern cold displaced farther south.
This mix of unusual heat and cold comes down to the jet stream. A strong difference in atmospheric temperature between the lower and higher latitudes causes the air current known as the northern hemisphere polar jet stream to flow between the Arctic and the middle latitudes. Sometimes, the difference in atmospheric pressure at different latitudes lessens, making the jet stream wavier. Warm air infiltrates the Arctic, and cold air infiltrates lower latitudes.
The cause of this wavy jet stream is being looked at closely. One facet getting scrutiny is the effect of a lower volume of ice in the Arctic Ocean. Arctic sea ice typically reaches its maximum extent sometime between late February and early April. Since the start of the 21st century, those winter maximums have declined. Although Arctic sea ice in 2018 hasn’t broken all previous records for its low wintertime extent, it’s still trending well below the 1981 through 2010 average.
Read Bryce’s weather blog at dtnpf.com.
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