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Weather Systems
Unit C Chapter 3 Lesson 1
Page s C64 -C69
Where Weather Occurs
Weather is the
condition of the
atmosphere at a
certain time and
place.
Atmosphere the lowest layer of
air where almost
all weather occurs
!
Measuring Atmospheric
Conditions
Scientists who study weather
are called meteorologists.
They use several kinds of tools
to measure weather. These
tools are called weather
instruments.
The weather changes because
the atmosphere is constantly
changing.
Weather Instruments
thermometer - measures air
temperature
barometer - measures air pressure
air pressure - the weight of the
atmosphere pressing in all
directions at a certain place
Weather Instruments
rain gauge - measures the
amount of precipitation
precipitation - water that
falls from clouds in the form
of rain, snow, sleet, or hail
hygrometer - measures
humidity
humidity - water in the
air
Weather Instruments
wind vane - shows the
direction from which the
wind is blowing
anemometer - measures
wind speed
Question 2
What are some atmospheric conditions that can
be measured?
Answer 2
air temperature, air pressure, precipitation,
humidity, wind direction, and wind speed
Air Pressure
The atmosphere pushes on you all the
time, and this weight is air pressure.
Warm air weighs less than cold air so
warm air rises.
Cold air is more dense so it sinks.
Air Pressure
When particles in the air are close together,
pressure is high.
When particles in the air are farther apart,
pressure is low.
Low air pressure usually means rainy or stormy
weather.
High pressure usually means fair weather.
Climate
Weather changes from day to day. It also changes
from season to season. But weather changes
follow certain patterns.
climate - the average of all weather conditions
through all seasons over a period of time
Temperature and precipitation are the major
factors that determine climate.
Weather in Mississippi
In the summer, the temperature in much of
Mississippi can reach 90F.
In the winter, the temperature sometimes gets
close to freezing, 32F.
Mississippi gets a lot of rain (51 inches a year)
but not much snow. The northern part of the
state gets a few inches of snow from time to time.
Drought
Drought - a long period with little or no rain
A drought makes the land dry. One result is that
plants, including farm crops, die.
Fires are also more likely when the land is dry.
To save water, people are asked to stop watering
lawns and to use as little water as possible.