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The 2010–11 North American winter was influenced by an ongoing La Niña, seeing winter storms and very cold temperatures affect a large portion of the continental United States, even as far south as the Texas Panhandle. Notable events included a major blizzard that struck the Northeastern United States in late December with up to 2 feet of snowfall and a significant tornado outbreak on New Year's Eve in the southern United States. By far the most notable event was a historic blizzard that impacted areas from Oklahoma to Michigan in early February which broke numerous snowfall records, and one of the few winter storms to rank as a Category 5 on the Regional Snowfall Index.
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 2010 occurred late on December 21 , and ends at the March equinox, which in 2011 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.