Transcript Ch 16 1 Weather

Ch. 16.1
What is weather?
Weather is
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The state of the atmosphere at a specific time
and place
Sun provides almost all of Earth’s energy
Air Temperature
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The measure of the average amount of
motion of molecules
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When temperature is cold molecules move slow
When temperature is hot molecules move fast
River Example
Warm=Fast
Cold=Slow
Wind
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Wind is air moving in a specific direction
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Named for the direction it is coming from
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Ex. Air that moves from west to east is called a west
wind.
Wind moves from areas of high pressure to areas
of low pressure
Measuring Wind
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Wind direction is measured using a weather
vane.
Wind speed is measured using an
anemometer.
Wind socks measure both speed and
direction.
Humidity
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Amount of water vapor present in the air.
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Warm air holds more water vapor.
Cold air holds less water vapor.
Relative Humidity
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A measure of the amount of water vapor
present in the air compared to the amount
needed for saturation at a specific
temperature.
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Saturation is a state in which something is
completely soaked with liquid.
Relative humidity is always
described as a percent.
Dew Point
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The temperature at which the air is saturated
and condensation forms.
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Dew point occurs when the air can’t hold any
more water vapor.
Measured in degrees
At 0°C, frost may form
This dew
Not this
Forming Clouds
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Clouds are formed when warm air is forced
upward, expands, and cools.
Water vapor condenses into tiny droplets on
small particles such as dust and salt in the
atmosphere.
Billions of these droplets form a cloud.
Stratus Clouds
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Form layers, or smooth even sheets in the
sky
Fog is an example of a stratus cloud
Cumulus Clouds
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Puffy, white clouds, with flat bases
Cumulus clouds look like cotton balls
Cirrus Clouds
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Cirrus clouds are thin, white feathery clouds
made of ice crystals
Cirrus clouds occur at higher elevations in the
troposphere
Cirrus clouds can indicate approaching
storms
Prefixes of Cloud Names
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Cirro- describes clouds at high a elevation
Alto- describes middle elevation clouds
Strato- describes clouds at low elevation
Example: Cirrostratus are smooth clouds at
high elevations of the troposphere.
Precipitation
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Clouds associated with rain or snow often
have the term Nimbus attached to them.
Example: Cumulonimbus clouds produce
thunderstorms.
Example: Nimbostratus clouds are layered
clouds that can produce long, steady, rainfall
or snow.
Rain
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Rain occurs when warm air rises, cools,
condenses
The dew point is reached, the air becomes
saturated and water droplets fall from the
clouds.
Snow
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Snow occurs when the air temperature is
below freezing.
Water droplets freeze and fall as snowflakes.
Sleet
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Sleet forms when the water droplets fall and
freeze before they reach the surface of the
Earth.
The temperature of the clouds are above
freezing.
The temperature close to the Earth surface is
below freezing.
Hail
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Hail forms in high level clouds where the
temperature is below freezing.
The water droplets in the clouds freezes.
The surface temperature of the Earth is
above freezing.