This is actually a complex situation with a cause that is related to the movement of the jet streams high up in the atmosphere and the location of Mount Washington. Every three days there is a change of wind movement as the low pressure hits the high at the north eastern corner of New Hampshire. This causes weather changes and Mount Washington is just at the spot where, up high, the action is happening.
Despite being in a temperate zone, and despite not being the highest peak in the Appalachians, Mount Washington has subzero temperatures all of the winter, sometimes as low as minus 50 degrees, matching Everest. Then, catching these weather changes, the wind speed lowers the temperature further. It's an unenviable place to visit, yet thousands do. Well somewhere had to gain the reputation of the world's worst weather, and Mount Washington has won it.