Early on in the winter season, a specific weather phenomenon can happen out in the Northeastern United States. When all the weather patterns and conditions are met, the phenomenon becomes what is known as “cold air damming.”
Cold air damming is a non-precipitative atmospheric phenomenon that occurs when high pressure systems move southward from eastern or southeastern Canada and deliver cold air masses to the greater part of the northeastern United States. The surrounding areas from the cold air mass, on the other hand, stay relatively warm because the cold air often gets stuck within valleys or other regions of lower elevation, typically in the vicinity of the Appalachian Mountains. The high pressure system is usually found in or close to the New England region during a cold air damming event, and its outwards clockwise circulation is what helps deliver colder air down in the vicinity of the Appalachians.
The reason why cold air damming is so impactful is not just because of high pressure in the northeast. Other factors are in play, such as the flow of the jet stream. When there is higher pressure near the poles, the flow tends to be more meridional, or more curvy with respect to flowing west to east. This is another factor that sends colder air from the poles and towards the equator. The Appalachians are also not the only place where one can observe cold air damming. Cold air damming can happen just east of the Andes in South America as well as the east of the Rocky Mountains in North America.
Depending on where cold air damming happens, specific weather events can occur as a result. Freezing rain can occur within the phenomenon when the warm air mass just outside of the trapped cold air mass rises over the cold air. Coastal ice storms and heavier snowfall during Winter-time along the East Coast of the United States can also be caused by the events of cold air damming. Knowing about the events associated with cold air damming ahead of time is useful for forecasters when predicting significant winter weather along mountain ranges.