Extreme jet stream causing record warmth in the east, record cold in the west

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2327

Posted by: Dr. Jeff Masters, 4:46 PM GMT on January 14, 2013

Los Angeles, California recorded its coldest temperature in 22 years on Sunday, and record daily lows fell across large portions of the Western U.S. over the weekend. But meanwhile, much of the Eastern U.S. basked in record-breaking warmth, with temperatures reaching the upper 60s in New York. What's going on? Well, the jet stream--the upper level river of strong winds that marks the boundary between cold, Arctic air to the north and warm, subtropical air to the south--has worked itself into a very extreme configuration.

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We've been seeing an increasing number of situations in fall and in winter in recent years where the jet stream has taken on the sort of extreme configuration that we are seeing today. Dr. Jennifer Francis of Rutgers has published research showing that Arctic sea ice loss may significantly affect the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. High-amplitude loops in the upper level wind pattern (and associated jet stream) increases the probability of persistent weather patterns in the Northern Hemisphere, potentially leading to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions. Arctic sea ice hit an all-time low during 2012 and remains near record low levels, so it is possible that Arctic sea ice loss contributed to the current extreme jet stream configuration, and the past week's spate of extreme temperatures on both sides of the U.S.