A strong weather system will bring the potential for flash flooding, severe thunderstorms, strong to locally damaging non-thunderstorm winds, and high elevation snow to the Hawaiian Islands. Precipitation will overspread most of the eastern third of the country. A prolonged atmospheric river will bring low elevation rain and mountain snow to the Pacific Northwest and California into the Rockies.
Washington's biggest winter storms are the great "Nor'easters". They get their name from the powerful northeast winds they produce. In order for a nor'easter to give Washington a large amount of snow, there must first be a source of cold air. High pressure builds over New England. The high's arctic air mass spreads south into the Washington area.
The dense, cold air tries to move west over the Appalachian Mountains, but it can not. It remains trapped on the east side funneling south over the coastal plain. East of the arctic air lies the warm water of the Gulf Stream. The contrast of the cold air sinking into the Carolinas and warm air off the Carolina Coast creates a breeding ground for storms. Combine the strong temperature contrast with other meteorological conditions such as the right position of the jet stream, and a storm's development can become "explosive" a sudden, rapid intensification; a dramatic drop in the central pressure of the storm.
Some meteorologists refer to this as a "bomb". For a good nor'easter to develop, the jet stream usually enters the West Coast of the US and splits. The north branch of the jet stream crosses over the northern Rockies and Canada.
It supports the southward sinking cold air. The southern branch dips down to the Gulf Coast states, then turns northeast across Virginia and rejoins the north branch near Newfoundland. The south branch of the jet stream carries a disturbance from the Gulf Coast to the Carolina Coast where it intensifies into a storm. Winds around the storm carry warm, moist air from over the ocean, inland.
