Imo the cold this winter(as well as some recent ones) was more a function of the EPO/WPO and the location of the TPV, which allowed for cross Polar flow and cold Arctic air to penetrate further south. The NAO was favorable at key times this winter, but overall fleeting. Just a matter of lucking into a storm chance at the right time, which is always a bit complicated for our region in a Nina. The AO state is always important for cold and snow chances at our latitude- Historically the number one indicator for above avg snow in DC is -AO. Some of this may be shifting however.