air mass
immense body of air that is characterized by similar temperatures and amounts of moisture at any given altitude
What is the common size for an air mass?
1600 kilometers across and several kilometers thick
What changes as an air mass moves?
the characteristics and the weather in the area under the air mass
What causes changes in weather patterns?
air masses
source region
area over which an air mass gets it characteristic properties
polar air mass (P)
forms at high latitudes near Earth's poles, usually cold ; describes the temperature characteristics of an air mass
tropical air mass (T)
forms at low latitudes near the equator, usually warm ; describes the temperature characteristics of an air mass
continental air mass (c)
formed over land , dry ; describe the moisture characteristics of an air mass
maritime air mass (m)
formed over water , humid ; describe the moisture characteristics of an air mass
What are the characteristics used to classify air masses?
overall temperature and the surface over which they form
What are the 4 types of air masses?
continental tropical (cT), continental polar (cP), maritime tropical (mT), and maritime polar (mP)
What is the weather in North America affected by?
continental polar and maritime tropical
What can the continental polar air mass cause?
cold and dry air in winter, cool and dry air in summer, brings clear skies in winter, brings light or heavy snow to leeward shores (known ad lake-effect snow), does NOT cause precipitation
What can a maritime tropical air mass cause?
most of the precipitation in North America, heavy precipitation, brings high temperatures and humidity to eastern and central US during the summer
What can a maritime polar air mass cause?
change from cold, dry, and stable to cool, moist, and unstable from Siberia to the US; accompanied by low clouds and showers; when it hits the western mountains, it causes heavy rain or snow
What can a continental tropical cause?
least influence on weather in North America; begin in southwestern US and Mexico during the summer; occasionally affect areas outside their source regions; causes an Indian summer
Indian summer
mild weather in the Great Lakes region in the fall; unseasonably warm and mild
nor'easter
storm characterized by snow and cold temperatures; caused by a maritime polar air mass