So what's causing all of this cold to suddenly evacuate the Arctic and ruin the onset of spring? As you see in the 2-6 day forecast of 500 millibar height anomalies from the European model above, record-breaking high pressure in the Arctic Circle is causing the Arctic Oscillation to go negative. For those unfamiliar with the term, the Arctic Oscillation involves a positive and negative phase. The positive phase has strong low pressure over the Arctic that locks cold up in the higher latitudes and allows warmth to prevail in the US. The negative Arctic Oscillation (AO) permits strong high pressure to take over the Arctic, which in turn allows cold air to flow freely into the United States. The Arctic Oscillation is forecast to reach a negative level that is so low it has not been seen since 2010. If the AO goes as low as the most extreme forecasts are calling for, we could see a negative level not experienced since 1985. Regardless of how low the Arctic Oscillation will go, the big picture is that cold weather will dominate the nation for the rest of March, likely into at least the first week or two of April. This event is not just a few days of chilly weather- we're talking multiple weeks of below normal temperatures. There is no end in sight to this colder weather at this time. I suppose this winter cold just got backordered.
For those of you who follow the idea that above normal snow cover in Siberia during October can make the Arctic Oscillation go negative in the following winter, this is a direct byproduct of that idea. The last third of October 2012 had way above normal snow cover, meaning we could be in for a month or more of below normal temperatures. Happy Spring!