The 2011–12 North American winter by and large saw above normal average temperatures across North America, with the Contiguous United States encountering its fourth-warmest winter on record, along with an unusually low number of significant winter precipitation events. The primary outlier was Alaska, parts of which experienced their coldest January on record.
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 2011 occurred late on December 21 (early on December 22 in EST), and ends at the March equinox, which in 2012 occurred on March 20 (March 19 in CDT and EDT). Based on the meteorological definition, the first day of winter is December 1 and the last day February 29. Both definitions involve a period of approximately three months, with some variability.
Seasonal forecasts
On October 20, 2011, the National Oceanic and Atmospheric Administration's Climate Prediction Center issued its U.S. Winter Outlook. The outlook expected the present La Niña to persist and intensify into the winter, resulting in drier than normal conditions in the drought-stricken states of New Mexico, Oklahoma, Texas, and parts of adjacent states. The CPC noted the significance of the less-predictable Arctic Oscillation, with CPC deputy director Mike Halpert saying, "The erratic Arctic Oscillation can generate strong shifts in the climate patterns that could overwhelm or amplify La Niña's typical impacts." The outlook was broken up into ten regions. The outlook anticipated above-normal wildfire conditions across the entire southern part of the United States, cooler and wetter-than-average conditions in the Pacific Northwest and western Montana, likewise for northern California, and drier-than-average conditions for southern California. Colder and wetter-than-average conditions were favored in the Northern Plains, but the converse was expected to occur in the Southern Plains and Gulf Coast states, worsening pre-existing drought conditions. In Florida and the southern Atlantic states, equal chances existed for below, near, and above-average temperatures, with below-average precipitation favored for the region and above-normal wildfire conditions. Equal chances for below, near, and above-average temperatures existed in the Ohio and Tennessee Valleys, with wetter-than-average conditions favored, resulting in an enhanced potential for storms and flooding. Equal chances for below, near, and above-average precipitation and temperatures existed in the Northeast and Mid-Atlantic states. The outlook noted that winter weather in this region often driven by the Arctic Oscillation rather than La Niña, and as such, if enough cold air and moisture were to coalesce, areas north of the Ohio Valley and into the Northeastern U.S. could expect above-average snowfall. Colder and wetter-than-average conditions were favored in the Great Lakes region, and above-average temperatures with above-average precipitation were favored in the western islands of Hawaii, resulting in the potential for elimination of drought, particularly in Kauai and Oahu. The outlook ended by noting chances favoring below-average temperatures in the southern half of Alaska and the panhandle with below-average levels of precipitation favored in the eastern interior region of the state.
On 4 January the lowest temperature of the winter was measured in Alaska: -56.6°C January was Alaska’s coldest since January 1965.