March Will End on a Cold Note
While many areas from the west coast and into the west slope of the Rockies have had a fairly mild March, all of the rest of the U.S., from the central Plains to the east coast has had a cooler than normal start to the month. For the rest of March we are expecting the cold to expand and include more areas of the lower 48 states. This will be especially true for the nation’s midsection, southeast states and the Mid-Atlantic.
One hint of what is to come for the last two weeks of the month shows up on our Arctic Oscillation Index. Notice that for most of the winter, the Arctic Oscillation Index has been negative (except for portions of January and February). Most recently, the Arctic Oscillation Index has gone strongly negative. Simply put, the strongly negative Arctic Oscillation Index means that there is a large amount of cold air in the northern latitudes that is between the North Pole and the lower latitudes. This places the cold air very close to the Continental United States and will make it very easy for storms to develop in the Pacific Northwest and slide southeast across the Central Rockies and into the Midwest and southeast states. As the storms move out of the Pacific Northwest and Canada, very cold air will spill into the plains states and will head east from there.
So be ready for a chilly second half of the month as well as some late season snows, especially in places that never saw a flake of snow in March 2012! Look for the best chances for precipitation to be along and just east and north of the average jet stream position.