by Nancy Houser

Created on: December 29, 2010

A look at the five basic types of air masses that determine the US's weather helps people better understand the upcoming weather forecast. First developed in 1920 by a Norwegian father and son team, Vilhelm and Jacob Bjerknes, understanding about air mass patterns help is better than taking someone's word for its accuracy – or inaccuracy. Air masses and atmosphere have become very important in determining the weather, with air developing its mass through a mixture of atmospheric gases. According to NASA, "Weather is the state of the atmosphere at some place and time." (

NASA.gov)

"Efforts at incorporating numerical data on weather into mathematical formulas that could then be used for forecasting were initiated early in the century at the Norwegian Geophysical Institute. Vilhelm Bjerknes and his associates at Bergen succeeded in devising equations relating the measurable components of weather, but their complexity precluded the rapid solutions needed for forecasting. Out of their efforts, however, came the polar front theory for the origin of cyclones and the now-familiar names of cold front, warm front, and stationary front for the leading edges of air masses ..." (University of St. Andrews, Scotland )

Air masses can be seen on any planet, at any given place or time, while involving a variety of weather formations. Air mass properties are dependent on the location of its formation, with high latitude air masses colder than low latitudes. Altogether, this forms the four basic types of air masses: cold and dry; cold and humid; warm and humid; and warm and dry.

What causes this are large groups or high volumes of air that are similar in humidity and temperature – called air masses. The National Weather Service Weather Forecast in Corpus Christi, Texas describes air masses "a large body of air that has relatively uniform temperature and humidity characteristics."(NOAA.gov)  This huge group is referred to as air mass source regions, acquiring the properties of the land beneath it if the mass remains over it long enough. Spring brings the most violent weather in the United States, caused by the clashing of the continental polar air and the maritime tropical air. This is described on weather maps with a K or W attached to the two-letter air mass description (cT, mT, mP, cP). The W refers to warmer air over the cooler land, while the K refers to a colder air mass moving over a warmer land mass.  

~ There are five basic types of air masses

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