The second type of snowstorm is called a Type B storm. This type of storm forms a primary low pressure center, usually in the Great Plains or Midwest. The storm tracks east or northeast towards the Appalachian Mountains. While this primary low is occluding over the Ohio Valley, a secondary low pressure center forms on the eastern side of the Appalachian Mountains, along the coast. This secondary low forms along the warm front of the primary occluded low, and then tracks up the east coast of the United States.
Throughout the twentieth century there have been various storms of both types. An example of a Type A storm, also known as primary development, is the storm that occurred on February 10-12, 1983. This storm developed along the Gulf Coast on February 10, dissipated off of the northeastern coast of Massachusetts on February 12, after dropping a large amount of snow along the east coast, from Virginia to Massachusetts. Anywhere from 13.5" to 22.8" of snow fell in the major metropolitan areas of Washington, D.C., Baltimore, Philadelphia, New York City, and Boston, but the most accumulation occurred in northern Virginia, Maryland, and northeastern West Virgina. To see the track that this storm took, click here!An example of a Type B storm, also known as secondary redevelopment, is the storm that occurred on March 2-5, 1960. This storm developed along the Gulf Coast on March 2, 1960, and tracked northeastward towards the Ohio Valley. Once it was over the Ohio Valley it occuluded, and a new low formed along it's warm front, near the South Carolina coast on March 3, 1960. the secondary low then proceeded to track up the eastern coast, and dissipated off of the coast of Massachusetts on March 5, 1960. Snow accumulations varied from 1" to 31" throughout New England and the Mid-Atlantic states. Major metropolitan areas did not see as much snow as they did with the Type A storm, however, severe blizzard conditions occurred in eastern Massachusetts, with heavy snow accumulations and near-hurricane force winds. To see the track this storm took,click here!
Type A : Primary Development - February 10-12, 1983
The conditions described here are typical for all Type A storms. A surface low forms over the Gulf of Mexico, or near the Gulf coast. The low tracks south of the Appalachian Mountains, and then northward up the east coast of the United States. When this is occurring, if there is a high pressure over northeastern Canada, the clockwise circulation around that high would bring cold air from Canada towards the east coast. As the low pressure center moves up the east coast, the counterclockwise circulation around the low brings with it warm, moist air from the south. As the cold air from Canada, supplied by the high pressure center, meets the warm, moist air from the south, supplied by the low pressure center, a coastal front forms. This front forms an enhanced region of precipitation. The heaviest precipitation falls to the north and west of the center of the low. Since the low travels northward up the east coast, the presence of below freezing air causes precipitation to fall in the form of snow. Hence, the major metropolitan areas of the northeast coast receive a lot of snow.
Type B : Secondary Development - March 2-5, 1960
The conditions described below are typical for all Type B storms. A surface low forms over the Midwest of the US, or over the Gulf of Mexico. It then tracks northeastward towards the Ohio Valley. Once it is near the Ohio Valley, just west of the Appalachians, a secondary low forms on the east side of the Appalachians, near the east coast. Again, a high pressure center over northeastern Canada supplies cold air to the east coast. As the secondary low begins to move northward up the east coast, the initial low dissipates. Again, the low pressure system that moves up the east coast brings with it warm, moist air. When the two contrasting air masses meet, a coastal front forms. An enhanced region of precipitation occurs near and along the front, with the heaviest precipitation to the north and west of the storm center. The presence of cold air ensures that the precipitation is in the form of snow.
Upper Air Dynamics
Surface features mentioned above for both types of storms are often assisted by upper level features. A jet streak, which is a region of maximum wind speeds, is situated over the surface low pressure center, helping to increase upward motion, which is needed to form precipitation. There is also another jet streak to the north and east of the previously mentioned jet streak. The two jet streaks actually work together to enhance upward vertical motion even more, therefore, causing more precipitation.
There is also a conceptual model called the conveyor belt that is used to help explain the airflow that is associated with a northeast coast snowstorm. There are three different conveyor belts: the warm conveyor belt, the cold conveyor belt, and the dry airstream (dry conveyor belt). The warm conveyor belt brings warm, moist air northward towards the low, and is what typically forms the "tail" of the comma that is characteristic of a cyclone, and seen on satellite imagery. The cold conveyor belt originates north of the low, within the high pressure system. It brings cold air southward toward the northern portion of the low, and forms the "comma head" that is typical of a cyclone. It is often under the head of the comma cloud that the heaviest precipitation falls. The dry airstream contains dry air that originates west of the low pressure center, and transports that air towards the surface low. It is the dry airstream that helps form the distinctness of the comma cloud shape. It is also at the junction of the dry airstream from the west, and the warm and cold conveyor belts from the south, and north respectively, that one will find the surface low.
Both surface and upper level features are illustrated in the schematic diagram shown below.