Objectives p. 52 Today, you will be able to: Explain How air masses affect weather Explain how air masses are classified

20 Chapter 20 Weather Patterns and Severe Storms Starter 1.What is a front? 2.Describe a sea breeze. 3.What is air pressure and where is it exerted? 4.Why does temperature increase in the stratosphere?

Local Breezes(p.51) Type of Breeze DirectionDay/NightCause Sea Land Valley Mountain

Local Breezes Type of Breeze DirectionDay/NightCause SeaToward land DaySun heats land faster than water; air above land rises creating low pressure zone LandToward sea NightLand cools faster than water; air above land sinks creating high pressure zone ValleyUpslopeDayAir along slopes heats faster than air above valley; glides up slope because it is less dense MountainDownslopeNightAir along slopes cools faster than air above valley; sinks down slope into valley

Reading Strategy(p. 51) Copy the table. After you complete this section, write a definition for each of the terms in the table. TermDefinition Air mass Polar air mass Tropical air mass Continental air mass Maritime air mass

Chapter Pretest 1.True/False- More water vapor can exist in warm air than in cold air. 2.When water vapor in air condenses, what must occur in order for clouds to form a.The air is heated b.Snow falls c. The air is cooled d. The air is superheated 3. What are low, sheetlike clouds called? a. Cirrus clouds b. Cumulus clouds c. Stratus clouds d. Cirrocumulus clouds 4. Where would the air contain the most moisture-over Kenya or over Antarctica? Why?

20.1 Air Masses  Air Masses An air mass is an immense body of air that is characterized by similar temperatures and amounts of moisture at any given altitude. As it moves, the characteristics of an air mass change and so does the weather in the area over which the air mass moves.

Frigid Canadian Air Mass Moves Southward How much warmer was the air mass when it reached Tampico, MX than when it formed?

20.1 Air Masses  In addition to their overall temperature, air masses are classified according to the surface over which they form.  The source region is the area over which an air mass gets its characteristic properties.

Maritime – forms over water Continental – forms over Land Tropical – Warm temperatures Polar – cold temperatures

The Air Masses cP( continental polar) : cold, dry stable Originates in Northern Canada cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface mP( maritime polar) : cool, moist, unstable mT( maritime tropical) : warm, moist, unstable

Air Masses Are Classified by Region

20.1 Air Masses  Much of the weather in North America, especially weather east of the Rocky Mountains, is influenced by continental polar (cP) and maritime tropical (mT) air masses.

20.1 Air Masses  Continental Polar Air Masses When a cP air mass crosses the great lakes it will pick up moisture. When this occurs in the fall/winter localized storms occur and are called, lake-effect snows.When this occurs in the fall/winter localized storms occur and are called, lake-effect snows.

 Maritime Tropical Air Masses Maritime tropical air masses are warm, loaded with moisture, and usually unstable. Maritime tropical air is the source of much, if not most, of the precipitation received in the eastern two-thirds of the United States.

20.1 Air Masses  Maritime Polar Air Masses 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 during its long journey across the North Pacific. Maritime polar air masses also originate in the North Atlantic off the coast of eastern Canada.

Weather in North America What is a Nor’easter? Resulting moisture is coming from the North East, thus the name Nor’easter. This is due to counterclockwise rotation of the Low pressure system drawing in maritime polar air.

Maritime Polar Air Masses

20.1 Air Masses  Continental Tropical Air Masses Occasionally cT air masses affect the weather outside their source regions. When a cT air mass moves from its source region in the summer, it can cause extremely hot, drought like conditions in the Great Plains. Movements of cT air masses in the fall result in mild weather in the Great Lakes region, often called Indian summer.

Air Mass & AbbreviationWhere does it form? Polar (____) __________ (T) Maritime (___) __________ (C) Air Masses and Abbreviations Air Mass Characteristics __________ (cP) Continental Tropical (___) ____________ (mP) Maritime Tropical (____) Complete chart using notes (actual chart is on the back of your notes)

Post-Test (page 52) 1.What is an air mass? 2.What happens as an air mass moves over an area? 3.How are air masses classified? 4.Which type of air masses have the greatest effect on weather in North America? 5.What kind of weather could be expected in Southern Canada if an mT air mass was to invade the region in mid-July?

Air Masses (page 53)

Air Masses Foldable (page 54) Create a four-door foldable with the four main air masses that affect weather in North America. Include: Name of the air mass (outside) Description (inside) Abbreviation (inside) Area of North America affected (inside)

Interpreting Temperature and Temperature Patterns (page 115)p.745

Building an Anemometer (page 123)