Understanding Weather

What is weather? The condition of the atmosphere at a particular time and place.

What is the water cycle? The process by which water recycles itself by continuous movement between Earth’s surface and the atmosphere.

What are the processes that “drive” the water cycle? (1 of 2) Evaporation – occurs when liquid water changes into water vapor, which is a gas Transpiration – the process by which plants release water vapor into the air through their leaves Condensation – occurs when water vapor cools and changes back into liquid droplets. This is how clouds form.

What are the processes that “drive” the water cycle? (2 of 2) Precipitation – occurs when rain, snow, sleet or hail falls from the clouds onto the Earth’s surface Runoff – water, usually from precipitation, that flows across land and collects in rivers, streams, and eventually oceans or lakes.

What is humidity? The amount of water vapor or moisture in the air.

How does air temperature affect humidity? As air temperature increases, the air’s ability to hold moisture increases.

What is relative humidity? The amount of moisture in the air compared with the maximum amount it can hold at a particular temperature. When air holds all of the moisture that it can at a particular temperature it is said to be saturated. Scientists use a psychrometer to measure relative humidity.

What is the dew point? The temperature to which air must cool to be completely saturated.

What is a cloud? A collection of millions of tiny water droplets or ice crystals that form as warm air rises and cools to become saturated.

What are the different types of clouds? (1 0f 2) Cumulus clouds – puffy, white clouds that tend to have flat bottoms. They form when warm air rises. Cumulus clouds can grow larger to become cumulonimbus clouds that produce thunderstorms. Cirrus clouds – thin, feathery, white clouds found at high altitudes. Form when the wind is strong. If they thicken and lower in altitude they can indicate approaching bad weather.

What are the different types of clouds? (2 0f 2) Stratus clouds - form in layers that cover large areas of the sky, often blocking the sun. Formed by a gentle lifting of a large body of air. Nimbostratus clouds are dark and usually produce light to heavy, continuous rain. Fog is a stratus cloud that forms near the ground.

Cumulonimbus Cumulus Stratus Cirrus

What is precipitation? (1 of 2) Water, in solid or liquid form, that falls from the air to the Earth. Rain – liquid precipitation that forms when water droplets become large enough to fall Snow – frozen water vapor that forms individual or clustered ice crystals that are heavy enough to fall Sleet – also called freezing rain, forms when rain falls through a layer of freezing air producing falling ice

What is precipitation? (2 of 2) Hail – solid precipitation that falls as balls or lumps of ice. Usually forms in cumulonimbus clouds where raindrops are blown by strong winds into higher altitudes where they freeze and fall. Repeated updrafts of wind continue this cycle adding layers of ice to the hailstone.

How is precipitation measured? An instrument called a rain gauge is used to measure the amount of rainfall. Snow is measured by both depth and water content. Snow’s water content is determined by melting the snow and measuring the amount of water.

What is an Air Mass? An air mass is a large body of air where temperature and moisture content are constant throughout Changes in weather are caused by the movement and interaction of air masses.

What is a source region? The area over which an air mass forms that affects the moisture and temperature characteristics of that air mass.

How are air masses represented on a map? They represented by a two-letter symbol where the first letter indicates the moisture characteristics and the second letter represents the temperature characteristics. m = maritime (forms over water; wet) c = continental (forms over land; dry) P = polar (forms over the polar regions; cold) T = tropical (develops over the Tropics; warm)

What is a front? Air masses with different characteristics do not usually mix. A front is a boundary that forms where two different types of air masses meet. Fronts usually occur in the middle latitudes because there are both cold and warm air masses.

What are the four different types of fronts? (1 0f 4) Cold front – forms when a cold air mass displaces a warm air mass because cold air is more dense than warm air which pushes the warm air up; they move fast and often produce cool temps, thunderstorms, and heavy rain or snow.

What are the four different types of fronts? (2 0f 4) Warm front - forms when a warm air mass meets and overrides a cold air mass gradually replacing the cold air; produces warm temps and drizzly precipitation.

What are the four different types of fronts? (3 0f 4) Occluded front – a faster moving cold air mass that overtakes a warm air mass and pushes it until it meets another cold air mass; produces cool temperatures and large amounts of precipitation

What are the four different types of fronts? (4 0f 4) Stationary front – forms when a cold air mass meets a warm air mass with little horizontal movement of air; the weather is usually similar to that produced by a warm front

What is severe weather? Weather that can cause property damage and even death.

What is a thunderstorm? Small, intense weather systems that produce strong winds, heavy rain, lightning, and thunder.

How do thunderstorms form? Form when warm, moist air near Earth’s surface rises rapidly through an unstable atmosphere. When the warm air reaches its dew point, the water vapor condenses forming cumulus clouds. If the atmosphere is extremely unstable the warm air will continue to rise, forming dark, cumulonimbus clouds.

What is lightning? Lightning is a large electrical discharge that occurs between two oppositely charged surfaces. When lightning strikes, energy is released and transferred to the air causing the air to expand rapidly. This causes sound waves which we call thunder. To insert this slide into your presentation Save this template as a presentation (.ppt file) on your computer. Open the presentation that will contain the image slide. On the Slides tab, place your insertion point after the slide that will precede the image slide. (Make sure you don't select a slide. Your insertion point should be between the slides.) On the Insert menu, click Slides from Files. In the Slide Finder dialog box, click the Find Presentation tab. Click Browse, locate and select the presentation that contains the image slide, and then click Open. In the Slides from Files dialog box, select the image slide. Select the Keep source formatting check box. If you do not select this check box, the copied slide will inherit the design of the slide that precedes it in the presentation. Click Insert. Click Close.

What is a tornado? Tornadoes are small, rotating columns of air that have high wind speeds and low central air pressure.

How does a tornado form? Wind traveling in two different directions causes a layer of air in the middle to begin to rotate. The rotating column of air is turned to a vertical position by strong updrafts from the cumulonimbus cloud. The updrafts of air also begin to rotate. The rotating column of air works its way down to the bottom of the cloud and forms a funnel cloud. The funnel cloud is called a tornado when it touches the ground.

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What is a hurricane? A large, rotating tropical weather system with wind speeds of at least 119 km/h. They are the most powerful storms on Earth. Most form between 5o and 20o north and south latitude because of warm tropical water.

What are the parts of a hurricane? Eye – the center of the hurricane, a core of warm, relatively calm air with low pressure Eye wall – strongest part, a group of cumulonimbus clouds that surround the eye producing heavy rains and forceful winds Rain bands – beyond the eye wall, spiraling bands of clouds producing heavy rains and winds

What is a storm surge? A wall of water that builds up over the ocean due to the heavy winds and low air pressure. A storm surge causes the greatest amount of damage from most hurricanes because of the flooding it causes.

What are some examples of equipment the meteorologists use to forecast the weather? (1 of 2) Thermometer – tool used to measure air temperature Barometer – an instrument used to measure air pressure Wind sock or wind vane - measure the direction of wind Anemometer – measures wind speed

What are some examples of equipment the meteorologists use to forecast the weather? (2 of 2) Weather balloons – carry weather equipment to make measurements at higher levels of Earth’s atmosphere Radar – used to find location, movement, intensity and type of precipitation Satellites – provide images of swirling clouds, and can measure wind speeds, humidity, and the temperatures at different altitudes

What are isobars? Lines on a weather map that connect points of equal air pressure.