Weather

Weather is… The state of the atmosphere at a particular time. heat vs. cold wetness vs. dryness calm vs. storm clearness vs. cloudiness

Air Mass A large body of air in which temperature and humidity is similar. Humidity – percent of water in the air Continental – mass formed over land Maritime – mass formed over oceans

Air Masses Affecting the U.S. Tropical Continental from SW deserts – bring dry hot weather in summer; none in the winter Maritime from Atlantic – bring hot, humid weather and thunderstorms in summer; mild, cloudy weather in winter Maritime from Pacific – bring moderate precipitation in the winter; none in the summer

Continued… Polar Continental from N. Canada – bring cool, dry weather in summer; very cold weather in winter Maritime from Pacific – bring rain and snow in winter; bring cool, foggy weather in summer Maritime from the Atlantic – bring cold, cloudy weather and snow in winter; cool weather with low clouds and fog in summer

What is a front? Front – the boundary that forms when two air masses with different temperatures (and densities) meet Cold Front – forms when a cold air mass takes over, and lifts up, a warm air mass Clouds may form in warm air Thunderstorms may occur ahead of fast moving cold fronts Squall lines may form

Fronts continued… Warm Front – forms when a cold air mass retreats from an area; less dense warm air rises over the cool air Produces precipitation over a large area

Fronts continued… Occluded Front – when an air mass lifts completely off the ground Stationary Front – when two air masses meet and they move parallel to the space between them

Plotting Weather Isotherm – lines that connect points of equal temperature Isobars – lines that connect points of equal atmospheric pressure Closely spaced – rapid change in pressure; fast winds Widely spaced – gradual change in pressure and winds Circles – indicate centers of high (H) or low (L) pressures

What do you see?