Continental arctic (cA), maritime polar (mP), maritime tropical (mT), continental tropical (cT), and continental polar (cP) air masses exist in and around North America. Clouds and thunderstorms can arise as a result of the turbulence created by the two moving air masses. The direction of travel for each type of air mass is indicated by the suffix of its name: cA travels from the Arctic to the Continental U.S., cP travels from the Continental U.S. to the Arctic, and so on.
The movement of air masses across North America has an enormous impact on local weather patterns. The interaction between these air masses and landforms creates different conditions over different regions.
The relationship between clouds and wind is important to understand because it determines what role clouds play in preventing solar radiation from reaching the earth's surface. Wind also influences the distribution of heat around our planet, especially at high levels where most global warming occurs.
Clouds are divided into three general categories based on how they form: liquid water droplets condense out from vapor suspended in air. These are known as precipitation clouds. Non-precipitating clouds contain particles that are larger than water molecules, such as ice crystals or dust. There are two main types of non-precipitating clouds: cirrus and stratus.
Arctic continental air is cold, dry, and clear while tropical continental air is hot, moist, and often cloudy.
The most common types of arctic continental air are known as polar fronts. They move over the Arctic Ocean and Canada with strong winds that bring very cold temperatures to eastern Canada and the United States. These conditions can cause snowstorms and ice storms when wind shifts occur as winter approaches.
As the name suggests, a polar front is made up of cold air from the Arctic Ocean that moves over warmer air from the continent. The polar front pushes south each winter, bringing with it cooler temperatures and more precipitation than normal across much of North America.
Maritime polar air is similar to continental polar air but does not affect land areas as strongly because it originates over open water instead of land. In fact, maritime polar air can only reach land at two places: the Canadian Maritime Provinces and Greenland. Over water, it behaves exactly like arctic continental air.
Contrary to popular belief, maritime tropical air does not come from the ocean; rather, it originates in the tropics.
When an air mass develops over land in the extreme north, it is referred to as a continental polar air mass. Cold and warm air masses typically collide in middle-latitude locations like the United States, where they create weather fronts and can cause major storms. These are some of the most damaging storms in North America.
Continental polar air masses do not directly reach the water because they are blocked by the continent. However, oceanic influences can reach far inland with tropical storm force winds and heavy rainfall. The atmosphere above a continental polar air mass will usually become more stable than normal mid-latitude air, which allows more severe weather events to develop.
In addition to continental polar air masses, large areas of the world's oceans are also surrounded by strong atmospheric conditions that block direct access from the ocean to the land. In this case, the air masses are called oceanic polar air masses. Because these masses do not contact land or water, they do not produce any rain or snow and their temperatures remain constant from surface to upper atmosphere.
Oceanic polar air masses can influence large regions because they move so slowly that they can stay over one area for several weeks or months at a time. For example, an oceanic polar air mass can travel across the central portion of the United States before it reaches Canada.
North America's weather is influenced by four major air masses. The continental polar and tropical air masses, as well as the maritime polar and tropical air masses, Because of the semi-permanent subtropical high pressure systems traveling south, the Continental Polar air mass dominates the United States in the winter. In the summer, because these same systems move north, the Maritime Polar air mass becomes more prevalent.
The continent-wide pattern of cold and warm air moving across North America is called the Great Loop. It causes differences in climate throughout the year. For example, in the southern part of our country it can get hot and humid in the summer, while up north people often need coats and boots for both seasons.
The main reason why there are so many different climates in North America is because we are almost 50 miles from the nearest land. This means that no foreign objects have been able to influence the weather here - no clouds, no rain forests, nothing but open space - which allows natural phenomena like wind and ice to have an impact on our weather.
There are two types of polar air masses: continental and maritime. In the continental polar air mass, cold air is pulled down from the Arctic region of Canada or Russia and then spreads out over Europe and Asia. In the maritime polar air mass, cool waters off the coast of North America cause cool air to flow into our area.
This air mass is responsible for thunderstorms in the Great Plains and elsewhere during the spring and summer. Continental tropical (cT) air masses are hot and dry, unstable at low altitudes, and typically stable in the atmosphere (upper-level ridge). As a cT air mass moves over cooler landmasses to the north or south, it begins to condense out moisture into clouds with intense precipitation that can produce severe weather.
A cP (continentally protected) air mass is similar to a cT air mass but with two important differences: first, it does not experience as much cooling from the continent; second, it is generally more stable than its tropical counterpart. Because cP air masses do not cool down as much, they can stay near the surface for longer periods of time, which allows more time for heat to be transferred into them from the ground or ocean. This means that people living in areas where cP air masses cause frequent tornadoes and hurricanes can expect such events year-round.
A Cfb (continental frontal zone buster) air mass is a cP air mass that has been influenced by the presence of a continental frontal zone. The influence of the frontal zone causes the air mass to become less stable, so less power is needed to lift it up into the atmosphere. These types of air masses can be found anywhere on Earth that experiences seasonal changes in temperature and precipitation.