Explaining the Brutally Cold Temperatures the U.S. has been Facing

The coldest air of the winter season is affecting millions from the northern Plains to New England this week, where temperatures are running well below average, and wind chills are plunging into dangerous territory. The cold weather is likely to stick around for much of the week, and repeated blasts of colder-than-average temperatures are anticipated into February as a possible result of a variety of factors, including a sudden warming event in the upper atmosphere above the Arctic, and a natural cycle of tropical rainfall variability near the Equator.

The turn to colder weather in much of the East may be related to two factors in particular. One is a sudden warming event that took place high in the atmosphere, in a region known as the stratosphere. This sudden stratospheric warming event, which occurred in late December into early January, may be drawing cold air away from the Arctic and into the northern mid-latitudes, while the Arctic enjoys relatively mild temperatures.

In addition to the sudden stratospheric warming event, there may be another natural climate phenomenon at work as well. According to Michelle L'Heureux, a climate scientist at the Climate Prediction Center, which is part of theNational Oceanic and Atmospheric Administration (NOAA), a phenomenon known as the Madden-Julian Oscillation, or MJO, also favors colder-than-average conditions in parts of the U.S. right now, and may even be a bigger factor than the more dramatic stratospheric warming event.

The MJO is associated with a pattern of tropical rainfall that moves eastward along the equator, going around the world in about 30-to-60 days. Because the MJO influences atmospheric heating through tropical rainfall, it can modify weather patterns far away from the equator.

http://www.climatecentral.org/news/is-there-a-tropical-link-to-frigid-air-gripping-wide-swath-of-us-15497