Air+Masses

=**__Objectives__**=

§ Compare the four major types of air masses and how they create fronts.
=//__Air masses__//=

How do they affect our Weather
=**//__Air Masses__//**=

== §  An air mass is a large body of air with relatively uniform temperature and moisture characteristics. The Sun’s heat (radiation) causes air masses to form and circulate in the atmosphere. ==

== §  Air moves both horizontally because of differences in pressure (wind) and vertically because it is forced to rise mechanically (when it encounters a mountain range) or because of changes in buoyancy. ==

=//__Continental Air Masses__//=

== §  __ Continental Arctic (cA): __ Extremely cold temperatures and very little moisture. These usually originate north of the Arctic Circle, where days of //__24 hour darkness__// allow the air to cool to sometimes record-breaking low temperatures. ==

== §  Such air masses often plunge south across Canada and the USA during winter, but very rarely form during the summer because the sun warms the Arctic. ==

== §  __ Continental polar (cP): __ Cold and dry, but not as cold as Arctic air masses. These usually form farther to the south and often dominate the weather picture across the USA during winter. ==

== §  Continental polar masses do form during the summer, but usually influence only the northern USA. These air masses are the ones responsible for bringing clear and pleasant weather during the summer to the North. == = = = = = = = = = = =**//__Continental Air Masses__//**=

== §  __ Continental Tropical __ (cT): Hot and very dry. They usually form over the Desert Southwest and northern Mexico during summer. They can bring record heat to the Plains and the Mississippi Valley during summer, but they usually do not make it to the East and the Southeast.==

== §  As they move eastward, moisture evaporates into the air, making the air mass more like a maritime tropical air mass. ==

== §   Continental tropical air masses very rarely form during winter, but they usually keep the Desert Southwest scorching above 100 degrees Fahrenheit during summer. ==

=WTBW 2/12/08=

=//__Maritime Air Masses__//=

== §  __ Maritime polar (mP): __ Cool and moist. They usually bring cloudy, damp weather to the USA. Maritime polar air masses form over the northern Atlantic and the northern Pacific oceans. ==

== §  They most often influence the Pacific Northwest and the Northeast. Maritime polar air masses can form any time of the year and are usually not as cold as continental polar air masses. ==

== §  __ Maritime tropical (mT): __ Warm temperatures with copious moisture. Maritime tropical air masses are most common across the eastern USA and originate over the warm waters of the southern Atlantic Ocean and the Gulf of Mexico. ==

== §  These air masses can form year round, but they are most prevalent across the USA during summer. Maritime tropical air masses are responsible for the hot, humid days of summer across the South and the East. == = = =__Air Mass Chart__=

§ Moisture Content
== §   Location (hint è  use lines of latitude)==