Download LESSON 20 TEKS: 3.8A, 4.8A, 5.2G, 5.3D, 5.8A Weather Conditions

LESSON 20
TEKS: 3.8A, 4.8A, 5.2G, 5.3D, 5.8A
Weather Conditions
The words in bold are vocabulary words that the student should be aware of.
When you turn on a TV or listen to a radio, you can hear a weather forecast. You can look up
what the weather will be like in your area on the internet also. How do weather scientists know
if it is likely to rain or snow or be windy tomorrow? They use tools to measure temperature,
precipitation, and more. These measurements help scientists understand what the weather is
now, and how it might change in the future.
Temperature
Weather is the condition of the atmosphere at a certain time and place. One factor that
influences weather is air temperature. A meteorologist is a scientist who studies weather.
Meteorologists use thermometers to measure the temperature of the outside air. Air
temperature is a measure of how hot or cold the air is. Weather forecasts usually report
temperature in degrees Fahrenheit ( ͦF).
Precipitation
Precipitation is water that falls from the atmosphere as
rain, snow, hail, and sleet. You can use a rain gauge to
measure the amount of rain that falls. This tool is a can or
tube with an opening on top. Rain falls into the rain gauge.
Marks and numbers on the side show how much rain has
collected in the rain gauge. Snow is measured with a snow
gauge, a tool similar to a rain gauge.
Humidity
Humidity is another important factor in describing weather. Humidity is the amount of
moisture, or water vapor, in the air. During the summer, the air feels more humid because
warm air can hold more moisture than cold air.

During the winter, when temperatures are colder, will the humidity be more or less than
during the summer? Explain why.
__________________________________________________________
Wind
Wind is moving air. Air moves because of differences in temperature
and humidity. Weather tools can measure two properties of wind –
direction and speed. A wind vane, or weather vane, shows wind
direction – where the wind is coming from. A wind vane spins freely in
the wind. It points in the direction from which the wind is blowing. If a
wind vane points east, the wind is blowing from the east.
An anemometer measures wind speed – how fast the wind is blowing. This
tool has several arms that stick out from a central rod. Each arm has a cup at
its end. Wind blows into the cups and spins the anemometer. The
anemometer counts how many times it spins in a given period of time. The
faster the wind is blowing, the faster the anemometer spins.
Air Pressure
Air pressure is the weight of the atmosphere pressing in all
directions at a certain place. Air pressure can change because air
particles can move farther apart or closer together. Cold air is
dense. Dense means that the particles are close together. Cold air
sinks because it is dense. Warm air rises because it is less dense.
When air rises, it can create an area of low pressure. When air
sinks, it can create an area of high pressure. Air moves from areas
of high pressure to areas of low pressure. The movement of air
from high pressure to low pressure areas is wind. Weather
scientists use barometers to measure air pressure.
Air pressure information is important for forecasting the weather. Changes in air pressure
mean that the weather is about to change. Low air pressure usually means rainy or stormy
weather. Suppose the weather is fair but the readings on a barometer are falling. Stormy
weather is probably coming. High air pressure usually means fair weather. If the air pressure is
rising, sunny weather is most likely on the way.

Are the particles of warm air close together or far apart?
______________________________________________________________
Weather and Climate
Weather changes from day to day. It also changes from season to season. But weather
patterns in an area tend to repeat over many years. A pattern is a repeated set of changes.
Climate is the average weather of an area over a long period of time. Scientists use weather
data gathered over many years to describe an area’s climate.
Temperature is a major factor in determining an area’s climate. The North and South Poles
receive little direct sunlight, so those areas have cold polar climates. The equator receives a lot
of direct sunlight, so that area has a very warm climate. Precipitation is another major factor in
determining an area’s climate.
Places near large bodies of water tend to receive a lot of
precipitation. Those areas have wet climates. Places such as deserts, don’t receive very much
precipitation so they have dry climates.

What are two main factors that determine an area’s climate?
______________________________________________________________________________

How are weather and climate different?
______________________________________________________________________________
________________________________________________________________________

A student wants to know how fast the wind is blowing. What tool should the student
use?
______________________________________________________________________________
Information on Weather Maps
Weather maps show what the weather is like in an
area at a certain time. A weather map of the
United States is shown below. Studying weather
maps helps scientists make predictions about what
the weather will be in the future.
A prediction is a statement about what is likely to
happen in the future. Weather maps show
temperature, precipitation, and other types of
weather data. The key tells you what each symbol
means.
The numbers on the map show
temperature in degrees Fahrenheit.
Weather maps help scientists follow the movement of air masses. An air mass is a large body
of air with the same temperature and humidity throughout. Humidity is the amount of water
vapor in the air. Humid air contains a lot of water vapor. An air mass can cover a very large
area. There are four basic types of air masses – cold and dry, cold and humid, warm and dry,
and warm and humid.
Weather maps often show air pressure. You may see circles with H’s or L’s on a weather map.
The H stands for “high” and indicates an area of high air pressure. The L stands for “low” and
indicates an area of low air pressure. High pressure areas usually bring fair weather. Low
pressure areas usually bring storms.
Weather maps also show fronts. A front is a place where two different air masses meet. On a
weather map, triangles show a cold front. Half circles show a warm front. The triangles and
half circles point in the direction that the front is moving.
At a cold front, a cold air mass bumps up against a warm air mass. Strong storms happen at
cold fronts. Thunderstorms are likely along cold fronts in warm weather. In winter,
snowstorms are likely along cold fronts. When a cold front passes over an area, the
temperature drops.
At a warm front, a warm air mass meets a colder air mass and slowly rides up over it. Sheets of
gray clouds form at warm fronts. They often bring rain. After a warm front passes over an
area, the temperature rises.
A stationary front forms when two air masses meet and stop moving. Clouds and precipitation
form at a stationary front.
COLD FRONT
WARM FRONT
Weather Patterns in the United States
In the United States, weather usually moves from west to east. Rain that forms over the Pacific
Ocean moves eastward over California. Rainstorms that form over the middle of the country
often move to the east coast within a day or two. The changing daily weather is due to the
movement of air masses.
Air masses behave in ways that can be predicted. When a cold, dry air mass bumps into a warm,
moist air mass, thunderstorms or snowstorms can occur. When a warm air mass rises up over a
cold air mass, the clouds that form can bring rain. Weather forecasters watch air masses across
the country. Tracking the air masses helps them predict the weather for the next few days.
QUESTIONS
1. What does a rain gauge do?
A. Tells what chemicals are in
rain
B. Measures how fast rain falls
C. Measures the amount of rain
that falls
D. Measures the size of
raindrops
2. What is an area’s average weather
over a long period of time called?
A.
B.
C.
D.
Seasonal weather pattern
Daily weather pattern
Climate
Precipitation
3. Which tool measures air pressure?
A.
B.
C.
D.
Barometer
Anemometer
Wind vane
Thermometer
4. Which would a meteorologist MOST
LIKELY study?
A.
B.
C.
D.
Weathering
Wind direction
Mixtures
Electricity
5. Mrs. Smith checks the internet
weather website every morning to
see how she should dress for work.
She also wants to know if she will
need an umbrella. She is checking
the –
A.
B.
C.
D.
Climate
Pattern
Weather
Forecast
6. On Monday, the rain gauge showed
2 cm of precipitation collected. On
Wednesday, the rain gauge showed
that 1 cm of precipitation had fallen.
On Thursday, the rain gauge showed
3 cm of precipitation collected.
What is the total amount of
precipitation that had fallen during
the week?
_________________cm.
7. What does a key on a weather map
tell you?
A.
B.
C.
D.
What today’s temperature is
What symbols on the map
mean
Where mountains are located
How to predict the weather
8. What does the letter H on a weather
map show?
A.
B.
C.
D.
An area of high air pressure
A high front
An area of high mountains
An area of high temperature
9. What is a front?
A.
B.
C.
D.
A place where air masses meet
The front part of a storm
An area of very high wind
An area that has fair weather
10. What does the “triangle” symbol
stand for on a weather map?
A.
B.
C.
D.
Stationary front
Warm front
Warm, dry air mass
Cold front
11. When you use a weather map to
make a prediction, you are acting
like –
A.
B.
C.
D.
An anemometer
A geologist
A meteorologist
A paleontologist
12. A student uses a wind vane and
records data for three days. What
data is the student collecting?
A.
B.
C.
D.
Precipitation
Wind speed
Temperature
Wind direction