Science High School Reviewer | Grade 4 Science | Earth Science | Weather and Climate | Lesson 23: Tracking the Weather

What are air masses and fronts?
The wettest place on Earth is in the state of
Hawaii. Rain falls over one of the islands about
350 days of the year. One of the driest places
in the world is a desert in South America. Some
parts have not seen rain for centuries! Why is it
so rainy in some places and dry in others?

Air Masses
The properties of the air in different places
on Earth vary. Large areas of air have nearly
the same properties. These regions are called air
masses. Weather in one part of an air mass is like
the weather throughout the rest of the air mass.
Air masses form all the time, usually near the
poles or the equator. They move across Earth,
covering it like an ever-changing blanket. The
map shows some of the common paths they take.

Fronts
As an air mass moves, it brings
weather with it. What happens when
different air masses meet? Like two
cars in a crash, the air masses slam
into each other. The area where they
meet is called a front.

A front is the boundary between
two air masses that have different
temperatures. Fronts usually cause
a change in the weather.

Warm Fronts
When a warm air mass pushes
into a cold air mass, a warm front
forms. As the diagram shows, the
warm air mass slides up and over
the cold air mass. Layers of clouds
form. The cold air retreats.
A warm front often brings light,
steady rain. After the front passes,
the air temperature rises.

Cold Fronts
A cold front forms when a cold
air mass pushes under a warm air
mass. The cold air mass forces the
warm air mass upward quickly.
Thick clouds form as the warm air
rises and cools. Cold fronts often
bring stormy weather.

Stationary Fronts
Sometimes rainy weather lasts
for days. This can be caused by a
stationary front. A stationary front is
a boundary between air masses that
are not moving.

What does a weather
map show?
Every day, scientists make
and share weather maps like the
one above. Weather maps show
weather conditions at a certain
time and place. They tell about air
temperature, pressure, precipitation,
and winds.
Weather maps may also show
the locations of fronts. The fronts
appear as a line of triangles or half
circles. In the map above, rain and
thunderstorms have formed along
the two cold fronts.

Forecasting
Maps can help us answer
questions. Scientists use weather
maps to make forecasts. To forecast
is to predict weather conditions.
Temperature, air pressure, and
the direction of moving fronts
give important clues for forecasts.
Look at the map again. Do you
see the cold front from St. Louis
to Houston? The triangles point
toward the east. Like most fronts in
the United States, this one is moving
from west to east. A forecast based
on this map may predict a chance
of rainy weather for New Orleans.
Scientists use many technologies
in forecasting. Satellites in orbit
around Earth take pictures of
the atmosphere. Computers help
scientists analyze weather data and
produce better weather maps.

What are the signs of
severe weather?
Have you ever heard a loud clap
of thunder just before a storm?
Thunder is the booming sound
made when lightning heats the air
around it quickly. Thunder tells you
that a storm is very near.
If you see a tall, swirling mass of
air shaped like a funnel, take cover!
It could be a tornado. A tornado is a
rotating column of air that touches
the ground during a thunderstorm.
Tornadoes can reach speeds of 400
km (250 mi) per hour or more!
A hurricane is a very wide storm.
A typical one spans about 480 km
(300 mi) across. Hurricanes form
over warm water in the ocean. They
bring very heavy rains and strong
winds. If a hurricane moves across
land, it can cause severe damage.
Storm Safety
Scientists pay close attention to
signs that severe storms are forming.
If one appears in their forecast, they
alert the government and the public.
Do you know how to stay safe in
severe weather? If thunderstorms are
predicted, stay away from water and
trees. When tornadoes are predicted,
head for a sturdy shelter, such as a
basement. To avoid a hurricane,
you may need to move inland.
In any storm, always listen for
directions. Seek out a trusted adult
if a severe storm strikes. Be sure to
follow warnings on the radio and
television.

Hurricane season (make it Rainy season? para relevant to Philippines)

June is the beginning of a busy time for the
National Hurricane Center in Miami, Florida. That’s
when hurricane season begins, and the scientists at
the center are ready for action.
Hurricanes develop at sea under particular
conditions. These include warm ocean water, low
pressure, moist air, and light winds. They usually
happen in the Atlantic and northeast Pacific Oceans
from June through November. When a hurricane
forms, it can bring violent winds, large waves, floods,
and lots of damage.
To study a hurricane, scientists gather large
amounts of data. Satellites that orbit Earth collect
information about cloud patterns. They record
temperatures on top of clouds and at the sea surface.
Satellites also measure the direction and speed
of winds above the ocean. This information helps
scientists track the size, path, and intensity of a storm.

Doppler radar is another tool that hurricane
scientists use. It sends out radio waves from an
antenna. Objects in the air, like raindrops, reflect
the waves back to the antenna. Doppler radar
can measure the direction and speed of a moving
object, like a hurricane moving toward land.
Buoys spread across the ocean measure
conditions like surface wind, waves,
temperature, and fog. Planes fly to
the center of a hurricane to gather
data about wind, pressure,
temperature, and humidity.
Scientists enter all of this data into
supercomputers to create a model of the
hurricane. This model helps them predict
the wind speed, size, and direction of
the hurricane, and where and when it
might hit land. Accurate predictions of
a hurricane’s path can reduce the loss
of life and property.