Transcript Weather

Weather
The state of the atmosphere at a
certain time and place
Climate
The average weather over a long
period of time
The Water Cycle
Water on Earth is constantly moving between the air, the
land, and the oceans and rivers in a process known as the
water cycle. To move from one region to another, the water
keeps changing from a liquid to a gas and back again.
Evaporation
– The Sun heats the water and the water changes into gas (water vapor).
Water vapor is in the air all around us. liquid  gas
Condensation
– As the warm air rises it cools and the water vapor becomes water
droplets again. gas  liquid
Precipitation
– Any form of water that falls from the sky (clouds); rain, sleet, snow, hail.
Run-off
– Gravity pulls the water downhill from higher ground to lower ground.,
through and over the rocks and soil.
– Forms streams which become lakes and rivers, eventually going back to
the oceans.
Influences on Weather
Humidity
– Humidity is the amount of water vapor in the air. Too much moisture in
the air can cause clouds which in turn can condense and fall to the
ground as precipitation.
Temperature
– A measure of how warm or cool the air is.
– Warmer air can hold more water vapor than cooler air. As warm air
cools precipitation can form.
Clouds
– Different kinds of clouds bring different weather and precipitation.
Air Pressure
– Low air pressure can bring warm temperatures, storms, and rain.
– High air pressure usually brings cooler temperatures and clear skies.
Wind
– Air moves from areas of high air pressure to areas of low air pressure.
Types of Clouds
Cirrus clouds
– the highest clouds. They are thin and wispy and made up of ice crystals.
They bring calm weather and they do not produce any precipitation.
Cumulus clouds
– mid to low level clouds that look like cotton balls. Small cumulus clouds
scattered across the sky indicate good weather. However as the clouds
grow larger they could produce rain.
Stratus clouds
– the lowest clouds. Fog is an example of this cloud. These clouds look
like a blanket and usually cover the entire sky. They can bring light rain.
Cumulonimbus clouds
– cumulus clouds that grow high into the sky. They often form
thunderstorm. Nimbus means precipitation.
Wind
The Prevailing Westerlies are winds which move weather
from west to east across the USA. They are responsible
for much of the weather we experience.
There are four different types of air masses that may
blow in and affect the local weather:
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Air masses that are cold and dry (Continental Polar)
Air masses that are hot and dry (Continental Tropical)
Air masses that are cool and moist (Maritime Polar)
Air masses that are warm and moist (Maritime Tropical)
Air Masses
 An air mass is a large body of air that has the
same temperature and level of humidity
throughout.
 They are described by their humidity and
temperature.
 They can be described as warm and wet, cold
and wet, warm and dry, or cold and dry.
 The interaction of air masses is what causes
changes in weather.
Fronts
The area in which two air masses meet but do not
merge (mix together) is called a front.
Cold Front
• Cold air moves under warm air causing the warm air to rise.
– Brings heavy rains, thunderstorms, and sometimes snow.
Warm Front
• Warm air mass moves up and over a cold air mass.
– Brings rainy, drizzly weather conditions, often followed by warm, clear
weather.
Occluded Front
• This is when a warm air mass is caught between to cold air masses
– Brings cool temperature and plenty of rain and snow.
Stationary Front
• This is when a warm air mass and a cold air meet but they do not
move each other.
– Brings many days of overcast, rainy weather.
A Cold Front symbol
– The direction that the teeth point indicates the direction
the front is moving.
A Warm Front symbol
– The direction that the bumps face is the direction
the front is moving.
An Occluded Front symbol
A Stationary Front symbol
–The symbol is a
combination of
a cold front and
a warm front symbol.
Cold Front
Warm Front
A fast moving cold air mass
A moving warm air mass
runs into a slow moving warm
collides with a slowly moving
air mass and the thicker cold
cold air mass and the warm air
air slides under the lighter
moves over the cold air.
warmer air.
Occluded Front
Stationary Front
A warm air mass is caught
A cold air mass and warm air
between two cooler air masses
mass meet, but neither air
and the thicker cold air masses
mass has enough force to
move underneath the thinner
move the other air mass.
warm air mass and push it
upward.
Weather Data
Meteorologists are scientists who study weather.
Weather information recorded over several years
determines the various climates on Earth. The data
collected allows meteorologists to make weather
predictions. Special tools are used to measure and
record this data.
Weather data can include
 air temperature
 air pressure
 humidity
 wind direction
 wind speed
 precipitation
Thermometer
A thermometer is a weather tool used to measure the
temperature.
Barometer
Barometers are important to measuring air pressure. Air
pressure can help you predict good or bad weather.
Hygrometer
Hygrometers are important for measuring air humidity.
Normal air humidity ranges from 50% to 75%.
Wind Vanes and Windsocks
By observing wind vanes and windsocks, we can know
the direction of the wind. Knowing the direction of the
wind is an important part in predicting the weather.
Anemometer
Wind speed is an important part of the weather. An
anemometer is a weather tool that measures wind speed.
Rain Gauge
A rain gauge is a weather tool used to collect rain.
Using measurements on the side of the rain gauge, you
can see how many inches it rained.
Geographical features influence weather and include
mountains and large bodies of water. They affect local winds
and breezes, and local temperatures.
Mountains
― affect temperatures as temperatures in mountainous regions tend to
be lower than those in flat areas.
The temperature of the air decreases as elevation (height) increases.
― affect precipitation by influencing patters of rainfall.
As the warm air mass approaches the mountain, it is forced to move
upward because of the shape of the mountain. As the air mass
moves upward it cools, causing condensation and precipitation. The
cool, dry air mass moves over the mountain and sinks, absorbing
moisture and heat from the land as it goes. The often produces a
desert on the other side of the mountain.
Bodies of Water
― water warms and cools more slowly than land.
― areas of land close to large bodies of water have milder weather
― the nearby water causes an increase in air moisture, so these areas
experience more precipitation
Winds and Breezes
Mountains and large bodies of water cause temperature differences,
which in turn, cause local winds.
Mountain and Valley
Breezes
The Sun warms the air above the
valley during the day. The warm
air rises and flows up the
mountain, causing a valley
breeze. At night, the mountains
cool down faster than the valleys
because of their elevation. The
cool air sinks and flows down the
mountain causing a mountain
breeze.
Sea and Land Breezes
During the day air over the ocean is cool forming areas of high pressure. Air
over the land is warmer, and as it rises, it creates an area of low pressure. The
cool, high-pressure air over the ocean flows towards the land creating a sea
breeze. At night, the air over the ocean is warmer than the air over the land, so
the warm low-pressure air over the ocean rises while the cool high-pressure air
over land sinks over and moves toward the ocean producing a land breeze.