Download Chapter 15: Weather

Chapters 12 Weather
*The possibility exists of us testing on chps 12 and 13 seperately
I. What is Weather?
A. Def.
1. Present state of the atmosphere and descriptions of current conditions
2. Factors Determining weather
a) air pressure
b) wind
c) temperature
d) amount of moisture in air
3. The interaction of air, water, and the sun cause weather
B. Humidity
1. The amount of water vapor held in the air
2. Amount of water vapor depends on temperature
a) cool air: cannot hold as much water vapor, condensation occurs
more quickly
b) warm air: can hold more water vapor, does not condense as
quickly
C. Relative Humidity
1. The measure of the amount of water vapor the air can hold at a specific
temperature
2. Saturated
a) air contains as much water vapor as it can hold
b) 100% Humidity
3. Dew Point
a) temperature at which air is saturated and condensation takes
place
b) changes depending on the amount of moisture in the air
D. Cloud Formation
1. Warm air is forced upward, expands and cools
2. As the air cools the amount of water needed for saturation decreases,
relative humidity increases
3. Relative Humidity reaches 100%
a) water vapor condenses around nuclei in the air
b) nuclei = dust, smoke, salt
4. The drops are so small they float in air
5. Millions of droplets form a cloud
E. Cloud Shape
1. Stratus Clouds
a) form layers or even sheets in the sky
b) form when layers of cool air dip below their dew point
c) Stratus cloud fog—layers of cool air near the ground reaches its
dew point and condenses
2. Cumulus Clouds
a) puffy white clouds with flat bases
b) form when air currents rise and cool
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c) can be associated with fair weather and thunderstorms
3. Cirrus Clouds
a) appear fibrous and curly
b) high, thin, white feathery clouds containing ice crystals
c) associated with fair weather but may indicate approaching
storms
F. Cloud Height
1. Prefixes of clouds describe cloud height
a) cirro: high clouds above 6000m
b) alto: middle clouds, 2000-6000m
c) strato: clouds below 2000m
2. Cirrostratus
a) high altitude
b) made of ice crystals
c) form halos around the moon and sun
3. Altostratus
a) middle altitude
b) thick sheets of gray or blue
c) produces light continuous precipitation
G. Precipitation
1. Water Falling from clouds
a) air temperature determines if it is rain, snow, sleet, or hail
2. Rain
a) drops of water falling in temps above freezing
3. Snow
a) air temperature is so cold that water vapor changes directly to a
solid (sublimation)
4. Sleet
a) snow passes through a layer of warm air
b) the snow melts and then refreezes near the ground
5. Hail
a) lumps of ice
b) form in cumulonimbus clouds of a thunderstorm
c) drops of water freeze in layers around a nucleus of ice
d) hailstones grow larger as they are tossed up and down by
convection currents in the clouds
II. Weather Patterns
A. Air Masses
1. Large body of air that has the same properties over which it develops
a) develops over land—dry air mass
b) develops over water—moist air mass
2. Examples of air masses
a) cT-continental tropical, warm dry air mass, forms over land
b) cP-continental polar, cold dry air mass, forms over land
c) mT-maritime tropical, warm moist air mass, forms over water
d) mP-maritime polar, cold moist air mass, forms over water
3. Air masses control the daily weather in an area
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B. Pressure Systems
1. Factors affecting air pressure
a) temperature
b) density
c) amount of water vapor
2. High Pressure
a) regions of descending air
b) dropping air makes it difficult for clouds to form
c) usually indicate clear good weather
d) move clockwise in the northern hemisphere
3. Low Pressure
a) regions of rising air
b) rising air forms clouds more easily
c) usually indicates cloudy, bad weather
d) low pressure systems move counter clockwise in the northern
hemisphere
4. Air blows out from a high pressure and into a low pressure
C. Fronts
1. The boundary between two different air masses
a) air with different characteristics do not mix
2. Warm Front
a) warm less dense air mass slides over a departing cold air mass
b) precipitation occurs over a large area
c) EX.
3. Cold Front
a) cold air mass pushes under a warm air mass
b) warm air is forced up
c) a narrow band of violent storms form
d) EX.
4. Occluded Front
a) two cool air masses merge
b) warm air between them is forced upward
c) strong winds and heavy precipitation occurs
d) EX.
5. Stationary Front
a) pressure differences cause a warm or cold front to quit moving
b) may remain in the same place for several days
c) cause light wind and precipitation across the entire front region
III. Forecasting Weather
A. Meteorologist
1.Studies the weather
2. Makes measurements on weather
a) temperature
b) air pressure
c) wind speed
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d) humidity
e) precipitation
3. They use the measurements to make weather predictions
B. Weather Forecasts
1. Weather Watches
a) possibility for severe weather
b) preparations should be made
2. Weather Warnings
a) severe weather is already happening
b) proper shelter should be found
C. Weather Information
1. Station Model
a) pg. 440 Figure 15-16
b) gives info on present weather conditions
c) all the info is used to make weather predictions
2. Isotherm
a) lines on a map connecting areas of equal temperature
b) very similar to contour lines
3. Isobar
a) lines on a map connecting points of equal atmospheric pressure
b) when isobars are close together this indicates areas of high
winds
c) when isobars are far apart this indicates areas of gentle winds
d) also indicates areas of high and low pressure on a weather map
e) H—high pressure L—low pressure
4. Symbols on a weather map
a) cold front
b) warm front
c) stationary front
d) occluded front
e) high pressure
f) low pressure
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Chapter 13 Material
A. Thunderstorms
1. Occur inside warm moist air masses and at fronts
a) warm moist air moves rapidly upward
b) air cools and condenses
c) forms a cumulonimbus cloud, can reach heights of 18km
2. Lightning
a) rapid uplift of air builds up electrical charges in clouds
b) some areas have opposite positive and negative charges
c) electrical current flows between areas of opposite charges
d) lightning can go between clouds or from the earth to the clouds
3. Thunder
a) rapid heating of air by lightning
b) lightning = 30,000oC (5 times hotter than the Sun)
c) extreme heat causes the air around lightning to expand rapidly
d) the air then cools and contracts quickly forming sound waves
4. Types:
Know the types identified in the text and how they form
B. Tornadoes
1. Violent whirling wind that moves in a narrow path over land
a) usually moves from southwest to northeast
2. Wind Shear
a) wind at different heights blows in different directions at
different speeds
b) a strong updraft will tilt wind shear and produce rotation inside
the thunderstorm (funnel cloud)
3. Not all funnels reach the ground
4. Tornadoes occur worldwide
a) most happen in the USA
b) over 700 tornadoes per year
C. Hurricanes
1. Large swirling low pressure system that forms over tropical oceans
a) must have winds of at least 120 km/hr
2. Steps of Formation
a) Low pressure develops over warm water
b) warm moist air is forced upward
c) the warm air cools and condenses
d) cool dry air sinks down the middle of the system
e) the moist air begins to swirl
3. Hurricanes draw their energy from warm moist water
a) after landfall they lose power and eventually break up
4. Called Hurricanes in the Atlantic Ocean
5. Called Typhoons in the Pacific Ocean
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