1. Weather Patterns & Severe Storms Ch 20:1

2. Air Masses and Weather Air Masses –An air mass is a large body of air that has similar temperatures and moisture content

3. Classifying Air Masses Source region – the area over which an air mass forms Air masses are classified by their temperature and by the surface over which they form

4. Classifying Air Masses Fig 3 Pg 560

5. Classifying Air Masses –Polar (P) – air masses that form at high latitudes toward the Earth’s poles – Polar air masses are cold –Tropical (T) – air masses that form at low latitudes – Tropical air masses are warm

6. Weather in North America Continental (c) – air masses form over land and are likely to be dry Maritime (m) – air masses form over water and are likely to be humid

7. Weather in North America Continental Polar Air Masses (cP) –uniformly cold/cool and dry Maritime Tropical Air Masses (mT) –Warm, loaded with moisture, and usually unstable –The source of most of the precipitation in the eastern two-thirds of the United States

8. Weather in North America Maritime Polar Air Masses –Begin as cP air masses in Siberia. The cold, dry continental polar air changes into relatively mild, humid, unstable maritime polar air as it travels across the North Pacific

9. Weather in North America Continental Tropical Air Masses –Only occasionally do cT air masses affect the weather outside their source regions. However, when a cT air mass moves from its source region in the summer, it can cause extremely hot, droughtlike conditions in the Great Plains –Movements of cT air masses in the winter across the Great Lakes region often cause “lake effect snow”