PRINCETON, N.J. —
The Arctic front brought a sudden change from spring-like temperatures to winter conditions when it passed through Denver on Tuesday. Before the front moved through, the temperature stood at a balmy 56°F on Tuesday at about midday. Just 5 hours later, temperatures cooled to 19°F. Many parts of Colorado may not exceed 15°F for nearly a full week.
A new storm system has started to form and it will move along this Arctic front, spreading freezing rain, sleet, and heavy snow from the lower Mississippi River Valley to the Upper Midwest. Dangerous accumulations of freezing rain are possible starting on Thursday in portions of Missouri, Oklahoma, Arkansas, and Illinois, according to the NWS.
Eventually, the wintry mess is forecast to extend along the Appalachians as the colder-than-average air slides eastward and mixed precipitation heads into interior portions of New England. The precipitation will be aided by an unusually strong jet stream aloft, with upper-level winds at about 30,000 feet exceeding 200 mph.
The weather pattern producing the cold air outbreak features a contorted jet stream that resembles a giant snake on a weather map, with a huge ridge of high pressure shunting the jet stream to the north of Alaska (bringing milder-than-average conditions there), only to come surging southward above the West and carving out a deep trough across the Central states.
Persistent areas of high pressure like the one over Alaska, as well as long-lasting unusual jet stream patterns, have caught the attention of some scientists who think such features may be becoming more common as the Arctic warms and sea ice declines. It’s an area of active research, with little consensus yet emerging from the meteorological community.
The cold snap means that 2013 will likely become the first year in 20 years in which record daily lows exceed record daily highs in the U.S. In a trend that is likely related in part to manmade global warming, there has been an increasing imbalance between record highs and lows during the past several decades, with record highs far outnumbering record lows.