1. Weather

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

3. 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

4. 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

5. 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

7. 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

8. 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

9. 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

10. 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

11. What do you see?