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Chapter 2: Understanding Weather Section 1: Water in the Air The Water Cycle – the continuous oceans movement of water from Earth’s ______ rivers into the __________, atmosphere in the & _____ ______, ______ & ground and back into the oceans _____ rivers - Humidity water vapor in the air * Amount of __________ * As the __________ temperature increases so does the air’s ability to hold water vapor - Relative Humidity – measures the amount water vapor in the air compared with of __________ maximum amount of water vapor that the _________ the air can hold at a certain temperature psychrometer * Measured using a ____________ - Condensation – process by which a gas (water vapor) becomes a liquid (water) * The air must be saturated ________ (100% relative humidity) * Can also occur when air cools to its dew point (the temperature at which ________ liquid gas becomes a _____) Clouds – a collection of small water droplets or ice crystals suspended in the air - Cumulus – puffy, white clouds that tend to have flat bottoms - ______ Stratus – form in layers & cover large areas of the sky & often block out the sun (____ Fog is a stratus cloud that has formed near the ground) - Cirrus – thin, feathery clouds found at high altitudes - Nimbo – or – nimbus indicate clouds that precipitation are likely to form __________ - Cirro – clouds formed at high altitudes - Alto – clouds formed at middle altitudes Precipitation – when water returns to Earth’s surface - Rain – most common - Sleet _____ – rain falls through freezing air & freezes into ice - Snow _____ – air is so cold that the water vapor freezes directly into ice - Hail – forms when raindrops are caught in an updraft & are carried into higher clouds where it freezes. As it starts to fall more water vapor attaches to the ice. The ice may be caught in another updraft & the outer water vapor freezes. This happens again & again until the ice ball is too heavy to be lifted by an updraft. The largest hailstone ever recorded was the size of a softball Let’s Review Weather is the condition of the atmosphere at a certain time and place. Weather is affected by the amount of water vapor in the air. The water cycle describes the movement of water above, on, and below Earth’s surface. Humidity describes the amount of water vapor in the air. Relative humidity is a way to express humidity. When the temperature of the air cools to its dew point, the air has reached saturation and condensation occurs. Clouds form as air cools to its dew point. Clouds are classified by form and by the altitude at which they form. Precipitation occurs when the water vapor that condenses in the atmosphere falls back to Earth in solid or liquid form.