WeatherThe state of the atmosphere at a

certain time and place

ClimateThe average weather over a long

period of time

The Water CycleWater 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 gasCondensation– As the warm air rises it cools and the water vapor becomes water

droplets again. gas liquidPrecipitation– 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.

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.

Types of Clouds

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:

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)

Wind

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.

FrontsThe 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 acombination ofa cold front and

a warm front symbol.

Cold Front

A fast moving cold air mass runs into a slow moving warm air mass and the thicker cold

air slides under the lighter warmer air.

Warm Front

A moving warm air mass collides with a slowly moving cold air mass and the warm air

moves over the cold air.

Occluded Front

A warm air mass is caught between two cooler air masses and the thicker cold air masses move underneath the thinner

warm air mass and push it upward.

Stationary Front

A cold air mass and warm air mass meet, but neither air mass has enough force to move the other air mass.

Weather DataMeteorologists 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 includeair temperatureair pressurehumiditywind directionwind speedprecipitation

ThermometerA thermometer is a weather tool used to measure the temperature.

BarometerBarometers are important to measuring air pressure. Air pressure can help you predict good or bad weather.

HygrometerHygrometers are important for measuring air humidity. Normal air humidity ranges from 50% to 75%.

Wind Vanes and WindsocksBy 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.

AnemometerWind speed is an important part of the weather. An anemometer is a weather tool that measures wind speed.

Rain GaugeA 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 BreezesMountains 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 BreezesDuring 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.