Chapter 5 Lesson 1 Describing Weather What is

Chapter 5 Lesson 1 Describing Weather

What is Weather? ØWeather is the atmospheric conditions, along with short-term changes, of a certain place at a certain time ØWeather can change quite rapidly, even within a few minutes, or a place can experience the same weather for a few days

Weather Variables ØMany things play a role in determining the weather ØSome weather variables include: ØTemperature ØRainfall ØAir pressure ØWind speed and direction ØHumidity ØCloud coverage ØPrecipitation

Who predicts the weather? ØA meteorologist is a person who is trained to predict the weather ØThey look at many specific variables before making an educated guess as to what the weather is going to be at a specific time

Air Temperature ØAir temperature is the average kinetic energy of molecules in the air ØWhen temperature is high, molecules have high kinetic energy ØMolecules in warm air move faster than molecules in cold air ØTemperature changes based on the time of day, season, location,

Air Pressure ØThe pressure that a column of air exerts on the air or a surface below it is called air pressure. ØAir pressure DECREASES with altitude (the higher up you go in the atmosphere, the less air pressure there is) ØAnother name for air pressure is barometric pressure ØAir pressure is measured with a tool called a barometer

Wind ØAir moves from areas of high pressure to areas of low pressure, creating wind. ØWind direction is the direction FROM which the wind is blowing ØWind speed is measured by meteorologists using a tool called an anemometer. ØWind direction is determined using a wind vane

Humidity ØThe amount of water vapor in the air is humidity ØWhen humidity is high, there is more water vapor in the air ØHumidity can make your skin feel sticky and your sweat may not evaporate as quickly as normal

Relative Humidity Ø Relative humidity is the amount of water vapor present in the air compared to the maximum amount of water vapor the air could have at a certain temperature Ø A good example to compare it to would be the amount of water a sponge can hold Ø At some point, the sponge can no longer hold any more water Ø Relative is measured using a psychrometer and is given as a percent Ø Air that has 100% relative humidity can not hold any more water or dew, otherwise rain will fall

Dew Point Ø When a sponge becomes saturated, it can not hold any more water and it begins to drip Ø The same happens when the air becomes saturated Ø When the air becomes saturated with water vapor, it will condense and form water droplets Ø If this happens, depending on the temperature, dew or ice crystals will form Ø If this happens higher in the atmosphere, clouds will form Ø When the temperature decreases, the air can hold less moisture. If the air becomes saturated, dew will form Ø Dew point is the temperature at which air is fully saturated because of decreasing temperatures while holding

Clouds and Fog Ø When air containing water vapor cools as it rises in the atmosphere and reaches its dew point, it condenses on small particles in the air and forms droplets Ø Surrounded by thousands of other droplets, these small droplets block and reflect light, making the visible as what we know as clouds Ø Clouds are water droplets or ice crystals suspended in the atmosphere Ø Different types of clouds form based on where they are located in the atmosphere Ø A cloud that is near Earth’s surface is known as fog Ø Fog is a suspension of water droplets or ice crystals close to or at Earth’s surface. Ø Fog reduces visibility, making it harder to drive

Precipitation ØRemember that water droplets in clouds form around small solid particles in the atmosphere such as dust, salt, or smoke ØPrecipitation occurs when cloud droplets combine and become big enough to fall back to Earth’s surface ØPrecipitation is water, in liquid or solid form, that falls from the atmosphere ØExamples of precipitation include rain, snow, sleet, and hail

Types of Precipitation ØRain is precipitation that reaches Earth’s surface in liquid form ØSnow is precipitation that reaches Earth’s surface in solid, frozen crystal form ØSleet is when snow melts as it falls through a layer of warm air in the atmosphere and then re-freezes ØHail starts as a small piece of ice that is repeatedly lifted and dropped by an updraft within a cloud. ØA layer of ice is added with each lifting

Water Cycle ØA series of natural processes by which water continually moves among oceans, land, and the atmosphere ØIncludes condensation, evaporation, and precipitation

Which is NOT a standard weather variable? a. Air pressure b. Moon phase c. Temperature d. Wind speed

What is a cloud near the surface of Earth? a. Snow b. Cumulus clouds c. Fog d. Precipitation

What is used to measure wind speed? a. Barometer b. Thermometer c. Wind vane d. Anemometer