Download Chapter 16-2 Weather Patterns Study Guide

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Chapter 16-2 - Weather Patterns Study Guide
Ms. Grady
Air Mass = large body of air that form over the same area and take on the
properties of that area.
For example, has the same temperature and humidity (amount of moisture
(water vapor).
 Air masses usually cover thousands of square kilometers.
Air masses are classified by where they form:
 Temperature
 Humidity
 There are 4 types of air masses in the United States.
Maritime polar Maritime Tropical Continental Polar Continental Tropical
(mP)
(mT)
(cP)
(cT)
 Forms over
 Forms over the  Forms over
 Forms over land in
the Pacific
ocean near the
land in
Mexico
Ocean in both
equator.
northern
 Brings dry, hot air
the winter
 It holds warm,
Canada
to the
and summer.
moist air
 In winter, cold
southwestern
 It forms
and dry air
states.
over the cold
masses cause
North
extremely cold
Atlantic
temperatures
waters in the
in the U.S.
winter.
 When it
collides
(crashes) with
a Maritime
Tropical (mT)
from Mexico,
then it could
cause a
tornado.
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Fronts
A front = 2 air masses that have different properties come together or
meet, they do not mix easily.
Therefore, a boundary forms between the 2 air masses. This is called a
front.
There are 4 types of fronts:
 Cold fronts
 Warm fronts
 Occluded fronts
 Stationary fronts
Cold front
 Forms when a mass of cold air meets and pushes under a mass of warm
air.
 The cold air mass forces its way underneath the warm air mass and pushes
it upward.
 Violent storms usually occur and then fair, cool weather comes after or
follows.
Warm front
 Forms when a mass of warm air overtakes a cold air mass and moves over
it.
 Rain showers follow by hot humid weather.
Occluded front
 A cold front travels faster than a warm front.
 When a cold front overtakes a warm front, then an occluded front forms.
 As warm air is pushed upward, the cold air meets the cool air.
 An occluded front may also happen when cool air overtakes a cold front
and warm air is pushed upward.
-It produces less extreme weather than a cold front or warm front.
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Stationary front
Stationary = not moving
 A warm air mass + a cold air mass meet and no movement happens so a
stationary front forms.
 What results (happens)? Rain may fall for many days in one area.
Storms or Severe Weather
 Storm = Violent disturbance in the atmosphere.
 Sudden changes in air pressure and rapid (quick) air movements
 Some storms cover a huge area, other storms only cover a small area.
Thunderstorms
 Cold front meets a warm air mass, cumulonimbus clouds produce
thunderstorms.
Violent downdrafts and strong wind shear
Lightning = electrical discharge.
 Lightning striking the ground is the main cause of forest fires.
 When the air is heated, it expands quickly. The quick expansion of the air
creates sound waves, or thunder.
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Cyclones and Anticyclones
 Air pressure has a huge effect (change) on the weather.
Cyclone = An area of low pressure that has rising warm air.
 In a cyclone, cooler air moves in to replace warm air. The air spins
around or spirals around and moves into the center of the cyclone.
 Cyclone – As the winds blow into a low pressure area they swirl/spin
counterclockwise direction in the Northern Hemisphere.
 Cyclones cause rainy and stormy weather.
 Anticyclones = the weather caused by high pressure systems.
 Anticyclones create fair, usually clear, and dry weather.
Tornadoes
 Tornado = whirling, funnel-shaped cloud.
 Tornadoes often form from a wall cloud (a type of cumulonimbus cloud)
Air pressure at the bottom of the funnel cloud is very low and can act like a
giant vaccum cleaner.
Water spout = A tornado over water.
 These are very common on the Great Plains.
 They can travel 95 km per hour.
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Fujita Scale
The Fujita scale ranks (orders/places, levels) tornadoes according to how
much damage they cause.
Only 1% is classified as an F5.
Hurricanes
 A hurricane =a very strong and powerful cyclone (hurricane/storm).
- The eye wall of the hurricane is the most deadly part.
 Typhoon = Hurricanes that forms over the western Pacific Ocean are
called typhoons.
 In the Indian Ocean they are called cyclones.
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 Hurricanes that affect the United States move from the Eastern
Atlantic near Africa to the northwest striking/hitting the East Coast
(usually between Florida and North Carolina).
Formation of Hurricanes – how they form
 Hurricanes form when warm, moist air begins to rise (go up) quickly.
Then cooler air moves in and it begins to spin.
 As the air pressure in the center drops (falls) what is happening is more
air is drawn into the spinning system. The system then begins to spin
faster.
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Damage of a Hurricane
 High waves and strong winds of a hurricane often cause a lot of damage.
-We see this mostly in the coastal areas.
-Heavy (lots of) rain can cause terrible flooding.
Meteorologists can watch and track the path of a hurricane (follow its path).
They can issue/send out Hurricane watches or warnings.
 Typical hurricanes last about 9 days.
-Other hurricanes may last 3-4 weeks
Severe Weather Safety
 The National Weather Service will issue/send out a watch or a warning
when severe weather will occur.
Watch – Stay tuned (listen) to a radio or television for instructions and be
prepared to take some type of action.
Warning – Immediately take action because the weather is here.
 Stay away from windows if there is a hurricane. If there is a snow
blizzard, go to a shelter or stay inside your house.