It's still early. There are more than ten weeks left before the vernal equinox marks the end of winter so there is still time for a few saving blizzards, but it is beginning to look like 2012 will be the Year Without Winter.
Temperature records are being set throughout the northern states. Less than 20% of the continental United States has snow cover, normally in mid-January it is about 50%.
By this date Buffalo, NY averages 38 inches of snow, this season just five inches. Lake Erie water is 5 degrees above normal and may not freeze up (once routine) for the third time in the last 15 years.
Milwaukee (avg. 15 inches, to date under two inches). Minneapolis (avg. 2 feet, this season ten inches). (source). The California snowpack, vital for summer survival in Los Angeles, sits at a microscopic 19% of average. A lack of snowfall in the Plains states means less groundwater for corn and wheat in the spring. Conversely, it has been a heavy winter in southern Alaska. Snow levels in the fishing village of Cordova are at 18 feet.
The jet stream has shifted well to the north keeping storm systems, that would normally track through the Plains states into New England, in northern Canada. This, in turn, is caused by a Positive Phase in the Arctic Oscillation2 (low Arctic atmospheric pressure) concurring with a strong La Nina.
La Ninas are caused by cool surface ocean temperatures in the tropical South Pacific which, in turn, are caused by an upwelling of cold water from the deep ocean. They are part of an oscillation with El Ninos when surface temperatures are unusually hot.
The Cause of the Cause3
Think of the global climate as a complex self-adjusting gear box. Think of carbon dioxide as a monkey wrench tossed into the works. If one gear loses a few teeth the other gears change to keep a circulation going. It may not be the same circulation we've grown used to but the machine doesn't care what the ball bearings think.
The Bering Sea gets warmer during Positive Phase Arctic Oscillation (and cools during increasingly rare Negative Phases). That means less heat exchange due to north-south current flows. This makes the El Nino/La Nina oscillation more prominent and has made this oscillation deeper and more frequent. That means more and more Americans will only be able to dream of a White Christmas. And in states like Texas, California, and Arizona water will be a commodity more valuable than gold or oil.
1 The science is far more complicated than this short, simplistic description.
2 Scientists are unsure as to the cause with explanations ranging from solar activity to the size of the Arctic ice pack. They do agree that in the last 40 years Arctic low pressures have become unusually common.
3My personal theory.