The GFS’ MOS temperature departure for Friday, Feb 22, 2013 is shown here. The primary weather features from the negative phase of the PNA are denoted in red, with a southward dip in the jet stream over the western U.S. while a ridge of high pressure becomes established downstream over the Southeast. But the negative phase of the NAO – whose impacts are denoted in blue, feature a southward building high over the Northeast and a cold north-northeasterly flow over the Mid-Atlantic. Negative phases of the NAO are actually warmer than normal for New England since the trajectory is more onshore – vs from Canada. You can see the PNA pattern “attempting” to warm up the eastern U.S., while the NAO does its best to keep the East Coast cold. The result is usually a mixed mess for Maryland.