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Chapter 2:
Understanding Weather
Section 1:
Water in the Air
The Water Cycle – the continuous
movement of water from Earth’s ______
rivers into the __________,
atmosphere in the
& _____
______ &
ground and back into the oceans
- Humidity
water vapor in the air
* Amount of __________
* As the __________
temperature increases so does
the air’s ability to hold water vapor
Relative Humidity – measures the amount
water vapor in the air compared with
of __________
maximum amount of water vapor that
the _________
the air can hold at a certain temperature
* Measured using a ____________
Condensation – process by which a gas
(water vapor) becomes a liquid (water)
* The air must be saturated
________ (100%
relative humidity)
* Can also occur when air cools to its
dew point (the temperature at which
gas becomes a _____)
Clouds – a collection of small water droplets
or ice crystals suspended in the air
- Cumulus – puffy, white clouds that tend
to have flat bottoms
- ______
Stratus – form in layers & cover large
areas of the sky & often block out the sun
Fog is a stratus cloud that has formed
near the ground)
- Cirrus – thin, feathery clouds found at high
- Nimbo – or – nimbus indicate clouds that
are likely to form __________
- Cirro – clouds formed at high altitudes
- Alto – clouds formed at middle altitudes
Precipitation – when water returns to Earth’s
- Rain – most common
- Sleet
_____ – rain falls through freezing air &
freezes into ice
- Snow
_____ – air is so cold that the water
vapor freezes directly into ice
- Hail – forms when raindrops are caught in
an updraft & are carried into higher clouds
where it freezes. As it starts to fall more
water vapor attaches to the ice. The ice
may be caught in another updraft & the
outer water vapor freezes. This happens
again & again until the ice ball is too heavy
to be lifted by an updraft. The largest
hailstone ever recorded was the size of a
Let’s Review
Weather is the condition of the atmosphere at a
certain time and place. Weather is affected by the
amount of water vapor in the air.
The water cycle describes the movement of water
above, on, and below Earth’s surface.
Humidity describes the amount of water vapor in the
air. Relative humidity is a way to express humidity.
When the temperature of the air cools to its dew
point, the air has reached saturation and
condensation occurs.
Clouds form as air cools to its dew point. Clouds
are classified by form and by the altitude at which
they form.
Precipitation occurs when the water vapor that
condenses in the atmosphere falls back to Earth in
solid or liquid form.