Observe two glasses of water. One filled with ice
water, and one filled with warm water.
Why do water droplets form on the outside of the
Where do the water beads come from?
Why don’t the water beads form on the warm
Explain how water moves through the water
Describe how relative humidity is affected by
temperature and levels of water vapor.
Describe the relationship between dew point
List three types of cloud forms.
Identify four kinds of precipitation.
Weather is the condition of the atmosphere at a
certain time and place.
The condition of the atmosphere depends on
how much water is in the air.
Understanding weather starts with understanding
how water cycles through the atmosphere.
The condition of the atmosphere is affected by
the amount of water in the air. Water in liquid,
solid, and gaseous states is constantly being
recycled through the water cycle.
The water cycle is the continuous movement of
water from sources on Earth’s surface into the air,
onto and over land, into the ground, and back to
Humidity is the amount of water vapor in the
The air’s ability to hold water vapor changes as
the temperature of the air changes.
Relative Humidity is the amount of water vapor
in the air compared to the maximum amount of
water vapor that the air can hold at a certain
Calculate the relative humidity by using the
actual water vapor content (g/m3)
relative humidity (%)
saturation water vapor content (g/m3)
Suppose that 1 m3 of air at a certain temp. can hold
24 g of water vapor. However you know that the air
is currently holding 18 g of water vapor. What is the
Assume that 1 m3 of air at 25°C contains 11 g of
H20(g). At this temperature, the air can hold 24
g/m3 of H20(g). Calculate the relative humidity.
A psychrometer is an instrument that is used to
measure relative humidity. A psychrometer consists
of two thermometers, one of which is a wet-bulb
The difference in temperature readings between
the thermometers indicates the amount of water
vapor in the air.
Condensation is the process by which a gas, such
as water vapor, becomes a liquid.
The dew point is the temperature at which a gas
condenses into a liquid.
A cloud is a collection of small water droplets or
ice crystals suspended in the air, which forms
when the air is cooled and condensation occurs.
1. Warm air rises and cools
2. Relative humidity of the air increases
3. Air eventually becomes saturated
4. Water vapor condenses on small particles in the
5. Millions of tiny water droplets collect to form a
Clouds are classified by form and altitude.
Cumulus clouds are puffy, white clouds that tend
to have flat bottoms.
Stratus clouds are clouds that form in layers.
Cirrus clouds are thin, feathery, white clouds
found at high altitudes.
Rain is the most common form of precipitation.
Sleet forms when rain falls through a layer of
freezing air. Snow forms when temperatures are
so cold that water vapor changes directly to a
Hail are balls or lumps of ice that fall from
What is the water cycle?
How are humidity and temperature related?
How do clouds form and what are the different
Identify the four kinds of air masses that
influence weather in the United States.
Describe the four major types of fronts.
Explain how fronts cause weather changes.
Explain how cyclones and anticyclones affect
Mr. Long will pour cooking oil (warm air mass)
and water (cold air mass) into the container.
Make a prediction about what will happen when
the two try to mix.
What happens when the liquids meet?
Was your prediction correct?
Using your results, hypothesize what would
happen if a warm air mass met a cold air mass.
Changes in weather are caused by the
movement and interaction of air masses.
An air mass is a large body of air where
temperature and moisture content are constant
Air masses get their characteristics from where
The characteristics of air masses are represent
by two letter symbols on maps.
The area in which two types of air masses meet
is called a front.
Cold Fronts A cold front forms where cold air
moves under warm air, which is less dense, and
pushes the warm air up.
Warm Fronts A warm front forms where warm
air moves over cold, denser air.
Occluded Fronts An occluded front forms
when a warm air mass is caught between two
colder air masses. Normally brings cold
weather and large amounts of rain or snow.
StationaryFronts A stationary front forms
when cold and warm air masses meet. The
air masses don’t have enough force to lift as
normal. Usually this produces many days of
cloudy, wet weather.
Cyclones are areas that have lower pressure
than the surrounding areas do.
Anticyclones are areas that have high pressure.
What are 3 places in the US you would like to
visit? What air masses commonly affect the
What type of weather is normally associated
with each type of front?
Write a one-paragraph description of a
thunderstorm. Describe the weather conditions
immediately before, during, and after the storm.
How does the storm affect each of your senses?
Describe how lightning forms.
Describe the formation of thunderstorms,
tornadoes, and hurricanes.
Describe the characteristics of thunderstorms,
tornadoes, and hurricanes.
Explain how to stay safe during severe weather.
Thunderstorms are small, intense weather
systems that produce strong winds, heavy
rain, lightning, and thunder.
They most often occur along cold fronts but
only two atmospheric conditions are required
to produce them
Warm moist air near Earth’s surface
Lightning is an electric discharge that occurs
between a positively charged area and a
negatively charged area. Thunderstorms are very
Thunder is the sound that results from the rapid
expansion of air along the lightning strike.
A tornado is a small, spinning column of air that
has high wind speeds and low central pressure
and that touches the ground.
A tornado starts out as a funnel cloud that pokes
through the bottom of a cumulonimbus cloud and
hangs in the air. The funnel cloud becomes a
tornado when it makes contact with Earth’s
Only about 1% of all thunderstorms produce
The US is home to about 75% of the world’s
They are most likely to occur during spring and
A hurricane begins as a group of thunderstorms
moving over tropical ocean waters. Winds
traveling in two different directions meet and
cause the storm to spin.
Hurricanes can cause a lot of damage when they
move near or onto land. Wind speeds of most
hurricanes range from 120 to 150 km/h.
Thunderstorm Safety Lightning is one of the
most dangerous parts of a thunderstorm. If you
are outside, stay away from trees, which can get
struck down. If you are in the open, crouch
Tornado Safety If there is a tornado warning
for your area, find shelter quickly. The best
place to go is a basement or cellar.
Flood Safety The best thing to do during a
flood is to find a high place to wait out the
Hurricane Safety If you live in an area where
hurricanes strike, your family should have a
disaster supply kit that includes enough water
and food to last several days.
What is the relationship between lightning
Why do hurricanes not form over land?
Tornadoes form from what type of cloud?
If you did not have the benefit of the weather
forecast on the news, radio, or television, how
would you forecast the weather?
Describe the different types of instruments
used to take weather measurements.
Explain how radar and weather satellites help
meteorologists forecast the weather.
Explain how to interpret a weather map.
Weather balloons carry electronic equipment
that can measure weather conditions as high as
30 km above Earth’s surface.
Measuring Air Temperature and Pressure A
tool used to measure air temperature is called a
thermometer. An instrument used to measure air
pressure is a barometer.
Wind direction can be measured by using a
windsock or a wind vane.
An instrument used to measure wind speed is
called an anemometer.
Radar is used to find the
location, movement, and amount of
precipitation. Weather satellites that orbit Earth
provide images of weather systems.
The National Weather Service produces weather
maps based on information gathered from about
1,000 weather stations across the United States.
Weather maps that you see on TV include lines
called isobars. Isobars are lines that identify
areas of equal, high, or low air pressure.
Whatdo each of the following instruments
Allimages and content were taken from
Holt, Rinehart, and Winston materials.