Download Chapter 18 Weather Patterns

BELL WORK:
Make sure you have the following written in your calender:
M – WB p 243-245
T – WB p. 250-252
W – Reading Weather Map Practice
T- Predicting Weather Practice
QUIZ: Chapter 18 terms on THURSDAY!!
CHAPTER 18
WEATHER PATTERNS
AIR MASSES
Air Mass
A huge body of air that has similar temperature, humidity, and air pressure at any
given height
Classified based on _________and __________.
Temperature
Humidity
Types of Air Masses in North America
1. Maritime Tropical
2. Continental Tropical
3. Maritime Polar
4. Continental Polar
Characteristics of the air mass depend on___ & ___
the air mass passes over as it forms.
Temperature of region & Moisture of the region
Temperature of Region:
Moisture of the Region:
Tropical
Maritime
Warm Air from tropics
Air from over the Oceans
Low Air Pressure
Very Humid Air
Polar
Cold Air from Poles
High Air Pressure
Continental
Air from over the Land
Dry Air
MARITIME
TROPICAL
Warm, humid air formed over tropical oceans
In summer:
Bring hot, humid weather
In winter:
Bring heavy rain or snow
If forms over Gulf of Mexico or Atlantic Ocean:
Moves 1st to SE United States  move N/NE and influence
weather in the central & eastern US
If forms over the Pacific Ocean(west):
Crosses the coastal mountain ranges and lose moisture
MARITIME
POLAR
Cold, humid air
Formed over the icy North Pacific and
North Atlantic Oceans
In Summer & Winter:
Bring fog, rain, cool temps to the west
coast
CONTINENTAL
TROPICAL
Hot, Dry air mass
Form mostly in summer over dry
areas in the Southwest and Northern
Mexico
Covers smaller area than other air masses
Move Northeast  bring hot, dry weather
to southern Great Plains
CONTINENTAL
POLAR
Form over central and northern Canada &
Alaska
Form near Artic Circle:
Bitterly cold with very low humidity
In Winter:
Brings clear, cold, dry air to much of North
America
In Summer:
Air Mass is milder
Storms may occur if continental polar air moves
south to collide with maritime tropical air
moving north
HOW AIR MASSES MOVE
Weather Changes when air mass moves and interacts with other
air masses.
In the U.S., air masses are commonly moved by:
1. Prevailing Westerlies
Major wind belts over U.S
Push air masses from west to east
2. Jet Stream
Bands of high-speed wind
Blow from west to east & carry air mass in the same directions
FRONTS
As air masses move over land & oceans:
They collide
Do NOT easily MIX
Less dense goes up/over the more dense air mass
Front
Boundary where air masses meet
Storms and changeable weather develop here
4 Main Types of Fronts:
1. Cold Front
2. Warm Front
3. Stationary Front
4. Occluded Front
COLD FRONT
A rapidly moving cold air mass runs into a slow moving
warm air mass
Denser cold air slides under the lighter warm air
Warm air is pushed up at the edge of the colder air
Expands & cools; reaches the dew point & clouds form
If a lot of water vapor in air = heavy rain/snow
If little water vapor in air = cloudy skies
Move quickly abrupt weather changes
After cold front passes, it leaves behind:
colder drier air with clear skies
shift in wind
lower temperatures
WARM
FRONTS
When a fast-moving warm air mass
overtakes a slowly moving cold air
mass
Accompanied by Clouds and precipitation
Due to density, the warm air moves over the
cold air
If warm air is humidlight rain or snow falls
If warm air is drydry, scattered clouds form
Warm air moves slowly = rainy or cloudy
weather for several days
After warm front passes, weather will be
warm and humid
STATIONARY
FRONT
When cold and warm air masses
meet BUT neither one can move the
other
Water vapor in the warm air
condenses into rain , snow, fog, or
clouds
Could last for many days
OCCLUDED
FRONT
When a warm air mass is caught
between two cooler air masses
Denser cool air masses move UNDER the less
dense warm air mass & push it UP
Two cool air masses
meet & mix & ground Temperature becomes
cooler
Warm air mass
cut off (occluded) from the ground
As it cools, water vapor condenses
Weather may turn cloudy & rain OR snow may fall
CYCLONES VS ANTICYCLONES
Both form when boundary between
two fronts becomes distorted and
bends develop along the front
Swirling center of LOW air pressure
Creates either a:
Winds spin INWARD
1. Low - Pressure Center
2. High - Pressure Center
Cyclones
Cyclones & decreasing air pressure cause:
Clouds
Wind
Precipitation
Anticyclones
Swirling center of HIGH air pressure
Winds spiral OUTWARD
Descending air inside causes:
Dry, clear weather
WEATHER FORECASTING
Meteorologist
Scientists who study the causes of
weather and try to predict it
Use maps, charts, and computers to
analyze weather data and to prepare
weather forecasts
Where do they get their information?
From National Weather Service
Weather Technology used by
National Weather Service
Weather Balloons
Upper troposphere and lower stratosphere
Measure temperature, air pressure, & humidity
Weather Satellites
In the Exosphere
Use cameras to
FORMATION
REGIONS
TYPICAL PATHS