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The chief suspect behind the mysterious weather is an atmospheric pressure pattern called the Arctic Oscillation, which circles the high Northern Hemisphere. Its lower edge is known as the North Atlantic Oscillation (NAO). Together, the related features influence the path and strength of the jet stream. The jet itself is an air current that flows west to east across the northern latitudes of the U.S., Europe and Asia, altering temperature and precipitation as portions of it dip southward or crest northward. A strong jet stream that flows in a somewhat straight line from west to east, with few southward dips, prevents cold arctic air from drifting south. "The cause of this warm first half of winter is the most extreme configuration of the jet stream ever recorded," according to Jeffrey Masters, a meteorologist who runs the Weather Underground, a Web site that analyzes severe weather data.
Meteorologists are not certain what causes the oscillations to vary so dramatically. Some scientists say the loss of Arctic sea ice due to global warming is causing the Arctic Oscillation to drop in pressure. Others have noticed a correlation with sunspot activity, which was very low in December 2010 and very high during December 2011, although they haven't proposed a mechanism whereby sunspots would directly alter the Arctic Oscillation.
An unusual region of atmospheric pressure over the Arctic has kept the polar jet stream (green) locked up at far northern latitudes, causing a warm, dry U.S. winter.
Originally posted by tetriswoooo
it wasnt just the usa here in australia we had a realy warm winter
The NAO is the dominant mode of winter climate variability in the North Atlantic region ranging from central North America to Europe and much into Northern Asia. The NAO is a large scale seesaw in atmospheric mass between the subtropical high and the polar low. The corresponding index varies from year to year, but also exhibits a tendency to remain in one phase for intervals lasting several years.
Originally posted by TransplantedArkansan
Our meteorologist here in Central AR says its a La Nina year,and the colder air has stayed up north.When this happens we usually see an early start to severe weather.
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Originally posted by St Udio
the strange weather is caused by a combination of forces/factors...
the La Nina of course,
but the trade winds & jet streams are being affected by an outside & more powerful force
which is the Earth's inclination of Its' orbit in relation to the Sun
just as some eras are abnormally cold... we are in the abnormally hot era---
because of the planets changing orbit... both the eccentricity and the inclination are different now than
what was normal for the last ~26,000 years
look it up