DISCUSSION: When it comes to anticipating rounds of cold air intrusions during a given Winter season, there is no doubt that one of the more interesting non-precipitative atmospheric phenomena which occurs is cold air damming. Cold air damming occurs most often during the early to middle parts of Winter when high-pressure systems sink southward out of eastern and/or southeastern Canada and deliver colder air masses to the greater part of the northeastern United States. As this process unfolds, there is a plethora of cold air which will often get “stuck” within valleys or any other regional areas of lower elevation. This phenomenon most often is famous for occurring along the East Coast of the United States in the vicinity of the Appalachian Mountains.
The premiere reason for why cold air damming is so impactful during any part of a Winter season has to do with several different factors which play a key role in association with cold air damming. Cold air damming typically occurs in the mid-latitudes as this part of planet Earth lies within the prevailing westerlies which is an area where frontal intrusions are more common during a typical calendar year. When the Arctic oscillation is in its negative phase and the regional atmospheric pressure is found to be higher over the polar regions, the flow is more meridional (i.e., more curvy flow with respect to the east-west plane), blowing from the direction of the pole towards the equator, which brings colder air into the mid-latitudes. It is worth noting that cold air damming is observed in the Southern Hemisphere just to the east of the Andes Mountains, with cool incursions sometimes observed as far equator-ward as the 10 degrees south. In the Northern Hemisphere, common situations occur along the east side of ranges within the Rocky Mountains system over the western portions of the Great Plains, as well as various other mountain ranges along the West Coast of the United States. The initial is caused by the poleward portion of a split upper level trough, with the damming preceding the arrival of the more equator-ward portion of the approaching upper level trough feature.
Furthermore, it is also important to acknowledge that some of the cold air damming events which occur east of the Rockies will go on to continue southward to the east of the Sierra Madre Oriental through the coastal plain of Mexico and down through the Isthmus of Tehuantepec. Further funneling of such cool air occurs within the Isthmus of Tehuantepec, which can occasionally lead to winds of gale and hurricane-force. Other common instances of cold air damming take place on the coastal plain of east-central North America, between the Appalachian Mountains and Atlantic Ocean which are the most common trigger mechanisms for coastal ice storms and heavier snowfall during Winter-time along the East Coast of the United States (and this is also reflected by the idealized graphic which is attached above courtesy of the National Weather Service network). In Europe, areas south of the Alps can also be quite prone to cold air damming which can help to support quite impressive snowfall events in the higher elevation regions spread across the span of the Alps. Lastly, in parts of central and eastern Asia, cold air damming has been documented near Taiwan and the Korean Peninsula which will often have similar consequences to cold air damming events which occur in other parts of the world.
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© 2018 Meteorologist Jordan Rabinowitz