Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 4:26 PM GMT on January 06, 2014
The most extreme cold air outbreak since 1994 is in store for much of the U.S. on Monday and Tuesday, as Arctic air behind a major winter storm invades the Midwest. The powerful 989 mb storm blasted the Upper Midwest on Sunday, bringing snows in excess of a foot over portions of Illinois, Michigan, Indiana, Missouri, and Ohio. The 11.4" that fell on Sunday in Indianapolis, Indiana made it that city's second snowiest day on record (the all-time record: 12.1" on March 19, 1906); Flint, Michigan also recorded its second snowiest day on record: 14.5" (the all time record: 15.0" on November 28, 1937.) A blast of Arctic air poured into the Upper Midwest on Sunday, and Sunday's playoff game between the Green Bay Packers and the San Francisco 49ers began with a temperature of 5°F and a wind chill of -10°, evoking memories of the legendary Green Bay Packers-Dallas Cowboys Ice Bowl NFL playoff game on December 31, 1967. On that frigid day, the temperature at kickoff was thirteen below zero, with a wind chill of -45°F. It's lucky that yesterday's game wasn't played today: the high temperature in Green Bay is expected to be near -10°, with wind chills as low as -40°. The temperature in Chicago at noon CST Monday was a remarkable -14°F, with gusty west winds of 20 mph causing a dangerously low wind chill of -40°. This is the 7th coldest noontime temperature ever measured in the Windy City (the record was -21° on January 10, 1982). The record-breaking cold air will spread eastward and southward over the next few days, bringing the coldest temperatures seen since January 1994 to many locations. The high temperature in Detroit on Tuesday is expected to remain below zero; the city's list of days with a high temperature below zero is a short one, with only three such days in recorded history. The frigid air is being propelled by strong Arctic winds of 15 - 25 mph, which will generate dangerously low wind chill readings in the -30° to -60°F range from Michigan to Minnesota on Monday and Tuesday. From the latest NWS Storm Summary, here are the coldest wind chill readings observed so far:
Comertown, MT: -63
Rolla, ND: -60
Grand Maraia, MN: -55
Hillhead, SD: -53
Mason City, IA: -48
Dexter, WI: -47
Figure 1. At my home in the northern Detroit suburb of Highland, Michigan, we got 14" of snow on Sunday, which made for some very low electrical output from my rooftop solar array! Photo by Ellie Masters.
The culprit: cold air from Canada and the polar vortex
In the winter, the 24-hour darkness over the snow and ice-covered polar regions allows a huge dome of cold air to form. This cold air increases the difference in temperature between the pole and the Equator, and leads to an intensification of the strong upper-level winds of the jet stream. The strong jet stream winds act to isolate the polar regions from intrusions of warmer air, creating a "polar vortex" of frigid counter-clockwise swirling air over the Arctic. The chaotic flow of the air in the polar vortex sometimes allows a large dip (a sharp trough of low pressure) to form in the jet stream over North America, allowing the Arctic air that had been steadily cooling in the northern reaches of Canada in areas with 24-hour darkness to spill southwards deep into the United States. In theory, the 1.5°F increase in global surface temperatures that Earth has experienced since 1880 due to global warming should reduce the frequency of 1-in-20 year extreme cold weather events like the current one. However, it is possible that climate change could alter jet stream circulation patterns in a way that could increase the incidence of unusual jet stream "kinks" that allow cold air to spill southwards over the Eastern U.S., a topic I have blogged about extensively, and plan to say more about later this week.
Figure 2. From wunderground's Jet Stream page, we see the large dip in the jet stream over the U.S. responsible for this week's extreme Arctic air outbreak.
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