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Weather

Temporary behavior of atmosphere (what’s going on at
any certain time)
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Small geographic area

Can change rapidly
Weather
--The study of weather is meteorology
Forecast is a prediction or estimate of future
events, especially coming weather
--Someone who studies weather is called a
meteorologist
Climate
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Long-term behavior of atmosphere (100+ years)
Large geographic area
Very slow to change
Severe weather
Refers to any dangerous meteorological phenomena
with the potential to cause damage, serious social
disruption, or loss of human life.
Temperature
a measure of how hot or cold something is; specifically, a
measure of the average kinetic energy of the particles in
an object, which is a type of energy associated with
motion.
Thunderstorms
Requires a mature cumulonimbus cloud
Signs
a.
b.
c.
Sudden reversal of wind direction
Noticeable increase in wind speed
Sudden drop in temperature
Thunderstorms
Possible weather:
a. heavy rains (flash floods)
b. lightning (forest fires)
c. thunder (frightens animals)
d. hail (crop damage)
e. tornadoes
f. strong, gusty winds
Thunderstorm by Brainpop
Lightning Storm
Cumulonimbus cloud becomes electrically charged and
ground below has opposite charge
Lightning stroke: flow of current thru air (a poor
conductor) from the – to the +
Lightning can flow from cloud to ground, cloud to cloud,
and from ground to cloud
Bright light is caused by glowing air molecules heated by
the current
Lightning follows the path of least resistance (easiest way
to positive)
Lightning rod offers lightning an easy, safe path to the
ground (+)
Thunder is the shock wave caused by the explosive
expansion of heated air
Sound travels @ about 1100 ft/sec in air
5,280 ft in one mile
Distance from you to lightning = number of seconds
between seeing the flash and hearing the thunder divided
by 5. (5,280 ft / 1100 ft/sec = 5 seconds)
Types of Lightning
Streak or bolt
a.
b.
Single or branched lines of light
Common in Puget Sound area
Sheet
a. shapeless flash over wide area
b. is cloud-to-cloud bolt hidden by the clouds
c. common in Puget Sound area
Other types of lightning
a. heat, ribbon, beaded (types of bolt)
b. ball (only other shape lightning can have)
Tornado (a.k.a twister, cyclone)
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Counterclockwise column of rotating air extending from
cumulonimbus cloud
Per square foot, is the most destructive atmospheric
event
Rated by wind speed (F1 to F5)
“Tornado season” = April, May, June
Tornadoes that form over water are called
“waterspouts”
Behavior of a tornado is unpredictable
Typical tornado will:
1. Occur between 3-7 pm
2. Travel 4 miles
3. Be 300-400 m wide
4. Travel 25-40 mi/hour
5. Have wind speeds up to 300 mi/hr
6. Produce extremely low pressure
7. Be dark due to debris picked up
Tornado by Brainpop
Lie flat in nearest ditch, etc.
At home
a. open windows, doors
b. seek shelter in basement or under heavy table in middle
of house
On the trail of a tornado
Tropical Cyclone
Nicknames
1. U.S.A.: hurricane
2. SE Asia, Japan: typhoon
3. Australia: willy-willy
Tropical Cyclone
Rated by wind speed (category 1 to 5)
Starts and grows over warm ocean water
Composed of bands of thunderstorms spiraling
counterclockwise around a low pressure center
Characteristics
Several hundred miles wide
Last many days (even weeks)
Winds from 74-200 mi/hr
Contains an “eye”

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a.
b.
c.
d.
Hurricances by Brainpop
Small region of low pressure
Surrounded by highest winds
Calm, peaceful, sunny weather
Last for about 1 hour as hurricane passes by
Safety Rules
Prepare for high winds
Prepare for flooding (greatest source of damage)


a.
b.
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Up to 20 in. of rain
Flooding by coastal water
3. Prepare for thunderstorms
4. Have on hand stored food, water, blankets, candles,
matches, radio, etc.
5. Seek shelter
Hurricanes Clip
Relative Humidity
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Measure of the amount of moisture in the air
compared to what the air could hold
How “full” of water the air is
Expressed as %
100% relative humidity = saturated air
Relative Humidity
Controlled by temperature
1. Warm air holds more moisture than cool air (more
space for water vapor between air molecules)
2. As air warms, relative humidity decreases
3. As air cools, relative humidity increases
What Factors Affect Weather & Climate?
1.
2.
3.
4.
The Sun
The Water Cycle
The Atmosphere
The Ocean
How Does the Sun Affect Weather?
It warms the atmosphere & oceans
It creates climate zones
It keeps the water cycle going
It affects weather patterns
The Water Cycle
All the water on the planet is recycled in this manner!
Parts of the Cycle
Evaporation—Water going from a liquid to a
gas (gains energy from the sun)
Parts of the Cycle
*Transpiration—evaporation of water from/out of
plants.
transpiration
Parts of the Cycle
Condensation—Water going from a gas to a liquid (cools or
loses energy)
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When this happens in the atmosphere, CLOUDS form.
Parts of the Cycle
Precipitation—when water falls out the atmosphere.
Forms when the water droplets in clouds become too
heavy to stay up.
Precipitation
Liquid water = rain

Frozen water = snow or sleet or
hail

The Water Cycle
Water Cycle by Brainpop
Water Cycle Advanced by Brainpop
How does the atmosphere affect
weather?
The atmosphere is a mixture of gases that
surrounds the Earth
Has five different layers; each has different
properties
We’ll label them in just a minute…
Air Temperature and Pressure change with
altitude
Weather occurs in the layer closest to Earth
(troposphere)
Write in the labels!
Exosphere
Thermosphere
Ionosphere
Mesosphere
Stratosphere
Troposphere
Ozone layer
Air Masses
= body of air with a certain
temperature and moisture level
Can be warm or cold
Can contain a lot of moisture or not a
lot of moisture
Fronts
= places where air
masses meet
4 Types: Warm, Cold,
Occluded, Stationary
Each kind can bring
different kinds of
weather
Occluded Front:
Stationary Front:
Science Saurus 221/222
& Reading a Weather
Map Worksheet
How does Air Pressure affect
weather?
How much the earth’s atmosphere is pressing down on us
Measured with a BAROMETER
If it CHANGES, then new weather is on the way:
Falling Air Pressure = stormy weather coming
Rising Air Pressure = fair weather coming
Steady Air Pressure = no change is coming
Winds = created from differences in air
pressure
Moves from areas of HIGH to LOW pressure
Greater the difference in pressure, the FASTER the wind
blows
Measured with wind vanes and anemometers or you
can estimate with the Beaufort Wind Scale
ScienceSaurus 224/225
Beaufort Wind Scale
Global Winds
Thousands of kilometers long; can cause
weather to move in different directions
Jet stream, prevailing westerlies, doldrums,
horse latitudes, trade winds
Big Winds Blowin’ Worksheet &
Science Saurus Section 217
Global Winds
Caused by the temperature difference in
different regions
Hot Tropical Regions—causes air to rise
 Cold polar Regions—causes air to sink
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Global Winds
Also affected by Earth’s Spin

Coriolis Effect = causes winds to curve to the right
in the N. Hemisphere; to the left in the S.
Hemisphere
Big Winds Blowin’ Worksheet
Dew Point

=Temperature at which the air is saturated (100%
relative humidity)
Several events can occur when the dew point temp. is
reached:
1. If dew point temp. is above freezing:
a. water vapor condenses as liquid
b. dew will form on surfaces
Dew Point
c. cloud droplets will form in air
2. If dew point temp. is below freezing:
a. water vapor condenses as a solid
b. frost on surfaces
c. snow (or hail) in the air
Humidity by Brainpop
1. What single factor controls humidity?
2. What temperature air can hold the most
water molecules?
3. What causes water to evaporate into the
atmosphere?
Rainbows
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Caused by sunshine on raindrops
White light (all colors) is refracted (bent) into colors as it
enters and exits the drop
To see a rainbow you must have the sun behind you
and raindrops in the air
Diagram:
Rainbow by Brainpop
How does the Ocean affect weather?
Ocean currents affect the temperature of the land they
pass by
Cold ocean currents = cooling effect
Warm ocean currents = warming effect
Temperature changes affect pressure – which then creates
WINDS
Winds blow this cooling or warming effect over the land
http://earth.rice.edu/MTPE/hydro/hydrosphere/topics/Ocean_Atm_Circ_ElNino.mov
http://www.wunderground.com/MAR/