The long spells of dry, tranquil weather observed earlier in the fall are usually just a memory in December. December continues in most years the stormy pattern which developed in the last part of November. In fact on average, for the nation as a whole, December is the stormiest month of the entire year. Almost every storm can bring snow or now even freezing rain to hamper travelers and holiday shoppers. Virtually any and sometimes all of the winter climatological storm tracks can be active by December.
Pacific storms can enter anywhere along the west coast.
Alberta lows move eastward through southern Canada or drop out of Canada across the northern Plains and Great Lakes. Colorado lows emerge from the west-central Plains and move towards the Great Lakes and St. Lawrence Valley. Oklahoma or Texas Panhandle lows fire up and accelerate either on a northeast trek across the central plains towards the Great Lakes or more eastward towards the Ohio Valley and mid-Atlantic or Northeast. Finally, Gulf of Mexico or east coast storms can make the weather very interesting for the Atlantic and Appalachian states. The regions with the highest frequency of low pressure this month are the Pacific Northwest, the western Plains, the Great Lakes and the Atlantic coast states.