This week's dramatic weather shifts in the Northeast and Middle Atlantic States are a sign of things to come, say NOAA National Weather Service scientists. The warm and dry winter came to an abrupt end in the region this week when the jet stream shifted southward and roared into the eastern U.S. bringing bitter cold temperatures, strong winds and snow.

These conditions, which include a series of southeastward surges of cold, arctic air led by fast moving storms, are likely to continue through the coming weekend and into the first part of next week. The Wednesday night through early Friday storm will be significant as eastern cities from Washington, D.C., through New York and Boston have the potential for significant snow and strong winds, and the entire Northeast will experience dangerous bitter cold air.

During the early part of the winter, the well anticipated La Niña brought typical storminess to the northwest U.S., with a storm track running from southwest to northeast through the Tennessee and Ohio Valleys and the Great Lakes. This storm track kept temperatures in the Northeast near normal or above normal. However, NWS scientists point to a phenomenon known as the North Atlantic Oscillation, or NAO, for the sudden change. When the NAO is in its "positive phase" conditions in the Northeast remain warm and dry during La Niña years. The NAO has recently held the jet stream farther north than normal keeping the polar air north of the Atlantic Coast. This week, however, the NWS weather models forecasted the NAO to turn "negative." This change dipped the jet stream toward the south allowing the rush of bitter cold polar air.

Thanks to La Niña and the North Atlantic Oscillation, NWS scientists say the bumpy ride this winter is expected to continue with rapidly changing weather conditions.

Local National Weather Service forecast offices are providing constant updates over NOAA Weather Radio, the local media and the Internet.