1. Part 5: Weather Patterns

2. Air Masses Large bodies of air
Movement of them causes changes in weather
Cover thousands of square kilometers
Properties fairly uniform
Classified by where they form
Continental – form over continents; relatively dry
Maritime – form over oceans; relatively humid
Polar – cold
Tropical - warm

3. 4 Major Air Mass Types in USA
1. Maritime tropical –
Forms over ocean near the equator
Warm, moist air
Most commonly affects Eastern states
In summer brings hot, humid weather
In winter brings rain or snow if it encounters a cold air mass

4. 4 Major Air Mass Types in USA
2. Maritime polar –
Forms over northern Atlantic and northern Pacific oceans
Cool, moist air
Bring cloudy, damp weather to Northeast and Pacific Northwest

5. 4 Major Air Mass Types in USA
3. Continental tropical –
Hot and very dry
Forms over the desert southwest and Mexico usually during summer
Affects southwest states, plains, and Mississippi valley and can bring record high temperatures

6. 4 Major Air Mass Types in USA
4. Continental polar –
Cold and dry
Forms over Canada
Often dominant weather in winter
Brings very cold weather
Can also bring clear, pleasant weather to the North in summer

7. Major Air Mass Types mT = Maritime Tropical mP = Maritime Polar
cT = Continental Tropical
cP = Continental Polar
cA = Continental Arctic (5th type)
Brings extremely cold temperatures with very
little moisture, originate north of the arctic circle in winter

8. Fronts
A front is a boundary that forms when two air masses with different properties meet
Weather is usually unsettled and stormy along a front.
4 types of fronts:
Cold
Warm
Occluded
Stationary

9. Cold Front Cold air mass meets and pushes under a warm air mass
Pushes warm air up
Can cause violent storms
Fair, cool weather usually follows a cold front
Generally move northwest to southeast
Can cause a rapid drop in temperature of more than 15° in one hour

10. Cold Front
Weather symbol: blue triangles point in the direction the cold front is moving

11. Warm Front Warm air overtakes cold air and goes over it
Showers followed by hot, humid weather
Noticeably warmer after the front passes
Generally move southwest to northeast

12. Warm Front
Weather symbol: Red, semicircles pointing in the direction the warm front is moving

13. Occluded Front A cold front moves faster than a warm front
When a cold front overtakes a warm front an occluded front forms
Usually form around low pressure areas
At the occluded front the cold air mass meets the cool air mass that was ahead of the warm front
Warm air rises to form cumulonimbus or nimbostratus clouds bringing precipitation

14. Occluded Front
Weather symbol: purple, alternating triangles and semicircles pointing in the direction the front is moving

15. Stationary Front When warm air meets cold air and no movement occurs
Rain may fall for many days
Weather Symbol: Alternating blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air