precipitation

precipitation from clouds

The most common precipitation comes from clouds. Rain or snow droplets grow as they ride air currents in a cloud and collect other droplets (Figure 1.2). They fall when they become heavy enough to escape from the rising air currents that hold them up in the cloud. One million cloud droplets will combine to make only one rain drop! If temperatures are cold, the droplet will hit the ground as snow. (a) Dew on a flower. (b) Hoar frost. (a) Rain falls from clouds when the temperature is fairly warm. (b) Snow storm in Helsinki, Finland. Other less common types of precipitation are sleet (Figure 1.3). Sleet is rain that becomes ice as it hits a layer of freezing air near the ground. If a frigid raindrop freezes on the frigid ground, it forms glaze. Hail forms in cumulonimbus clouds with strong updrafts. An ice particle travels until it finally becomes too heavy and it drops. (a) Sleet. (b) Glaze. (c) Hail. This large hail stone is about 6 cm (2.5 inches) in diameter. Click image to the left or use the URL below. URL:

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dew and frost

Some precipitation forms in place. Dew forms when moist air cools below its dew point on a cold surface. Frost is dew that forms when the air temperature is below freezing.

precipitation

Precipitation (Figure 1.1) is an extremely important part of weather. Water vapor condenses and usually falls to create precipitation.

instructional diagrams

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questions

hail forms from the strong updrafts of these clouds.

a) cumulous

b) stratus

-->  c) cumulonimbus

d) cirrus

when raindrops freeze on the ground they make

a) sleet

b) hail

-->  c) glaze

d) snow

frost only forms in winter.

a) true

-->  b) false

when a surface is colder than the surrounding air, the air in contact with that surface may cool enough to form this type of precipitation

a) glaze

-->  b) dew

c) hail

d) fog

when falling rain turns to ice in the freezing air near the ground it becomes

-->  a) sleet

b) hail

c) glaze

d) snow

for a hailstone to get really large there must be

a) high humidity in the cloud to provide enough water to build up the ice.

b) a layer of freezing ground near the surface for the drop to freeze solid.

c) low wind conditions so the hailstone can form without being blown around.

-->  d) strong updrafts to keep the ice in the cloud while it builds up.

most precipitation occurs when water vapor condenses and the droplets come together.

-->  a) true

b) false

what causes rain droplets fall when they

a) condense.

-->  b) are heavy enough to escape the rising air currents.

c) melt since they start out as ice crystals in a high cloud.

d) none of these.

diagram questions

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