Pacific ridging has been leading to a particularly rough winter across the Aurora area and the eastern United States in general. According to National Weather Service statistics, O'Hare Airport has received 36.5 inches of snowfall for the season through January 17th. Through January 17th of last year, the area had seen a shockingly low 1.3 inches of snow! The area has already officially seen 11 days this season when the temperature has dropped below zero. The last two winters combined, 2011-2012 and 2012-2013, only saw 1 day drop below zero! The 23.1 inches of snow the area saw between December 30th, 2013 and January 5th, 2014 was also the 7th snowiest week in Chicago history! December as a whole ran 4.4 degrees below normal. January is running 6.2 degrees below normal.
A strong eastern Pacific ridge due to a negative Eastern Pacific Oscillation is responsible for this strong winter in the area. A large ridge of high pressure has largely positioned itself in the Gulf of Alaska the last couple of months. This has largely kept the west coast warm and dry this winter. Temperatures in southern Alaska were actually in the lower 40's yesterday. This intrusion of warmer air to the north pokes into the arctic and displaces cold air to the south. As the jet stream buckles up so far north in the west, it has to buckle down further downstream in the United States. The displaced cold air is then pulled down by the buckled jet stream into the eastern United States. There are no signs of this pattern breaking down anytime soon, and it should continue through the end of January.