The 2013–14 North American winter was one of the most significant for the United States, due in part to the breakdown of the polar vortex in November 2013, which allowed very cold air to travel down into the United States, leading to an extended period of very cold temperatures. The pattern continued mostly uninterrupted throughout the winter and numerous significant winter storms affected the Eastern United States, with the most notable one being a powerful winter storm that dumped ice and snow in the Southeastern United States and the Northeastern United States in mid-February. Most of the cold weather abated by the end of March, though a few winter storms did affect the Western United States towards the end of the winter. While there is no well-agreed-upon date used to indicate the start of winter in the Northern Hemisphere, there are two definitions of winter which may be used. Based on the astronomical definition, winter begins at the winter solstice, which in 2013 occurred on December 21, and ends at the March equinox, which in 2014 occurred on March 20. Based on the meteorological definition, the first day of winter is December 1 and the last day February 28. Both definitions involve a period of approximately three months, with some variability. Seasonal forecasts On November 21, 2013, the National Oceanic and Atmospheric Administration's Climate Prediction Center issued its U.S. Winter Outlook. Sea surface temperatures had been near average since spring 2012, and forecasters expected these conditions to continue through winter 2013–14, with neither El Niño nor La Niña conditions expected to affect the season's climate. In the outlook, little rainfall was anticipated in the Southwestern United States, and the development of drought was expected in the Southeastern United States. Below-average levels of precipitation and below-average temperatures were expected in the Alaskan panhandle. Below-average temperatures were also favored in the Northern Plains, while above-average temperatures were favored in New England, the South-Central, Southeastern, and Southwestern United States, and western Alaska. The remainder of the country fell into the outlook's "equal chance" category, with an equal chance of above-average, below-average, and near-average temperatures and/or precipitation. Events October storm complex The first winter storm of the season, a significant system, was forecast by the National Weather Service, which issued a Blizzard Warning on October 3 preceding the storm. The storm occurred as an early season blizzard, and, according to the Weather Prediction Center,