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 holds more water vapor than cooler air. As warm air cools condensation begins and 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. Cloud Types A cloud is a collection of millions of tiny water droplets or ice crystals. 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 level clouds that look like cotton balls. Small cumulus clouds scattered across the sky indicate good weather. However as the clouds grow larger and darker 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 – these are cumulus clouds that grow high into the sky. They often form thunderstorms. 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: 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 temperature and humidity. They can be described as warm and moist, cool and moist, hot and dry, or cold and dry. The interaction of these different air masses 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 A warm air mass is caught between to cold air masses – Brings cool temperature and plenty of rain and snow. Stationary Front A warm air mass and a cold air meet but they do not have sufficient energy to 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 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 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 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 Influences Geographical influences include mountains and large bodies of water. They affect local winds and breezes. Mountains ― affect temperatures; temperatures in mountainous regions tend to be lower than those in flat areas as the temperature of the air decreases as elevation (height) increases. ― affect precipitation by influencing patterns 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.