Ch 16 Weather

Front 1

cirrus cloud

Back 1

Cirrus clouds form high in the troposphere. Because it is so cold they are made of ice crystals. They are thin and wispy. Cirrus clouds don’t usually produce precipitation, but they may be a sign that wet weather is coming.

Front 2

cumulus cloud

Back 2

Cumulus clouds are white and puffy. Convection currents make them grow upward and they may grow very tall. When they produce rain, they are called cumulonimbus.

Front 3

dew point

Back 3

The temperature at which water vapor condenses is called the dew point. If this temperature is below freezing, ice crystals of frost form instead of dew.

Front 4

fog

Back 4

Clouds form when air in the atmosphere reaches the dew point. Clouds may form anywhere in the troposphere. Clouds that form on the ground are called fog

Front 5

freezing rain

Back 5

Freezing rain falls as liquid water. It freezes on contact with cold surfaces near the ground. It may cover everything with a glaze of ice. If the ice is thick, its weight may break tree branches and pull down power lines

Front 6

hail

Back 6

Hail is another type of frozen precipitation. Hail forms in thunderstorms when strong updrafts carry rain high into the troposphere. The rain freezes into balls of ice called hailstones. This may happen over and over again until the hailstones are as big as baseballs. Hail forms only in cumulonimbus clouds.

Front 7

heat index

Back 7

The heat index is a measure of what the temperature feels like because of the humidity.

Front 8

humidity

Back 8

Humidity is the amount of water vapor in the air. High humidity increases the chances of clouds and precipitation.

Front 9

relative humidity

Back 9

Humidity usually refers to relative humidity. This is the percent of water vapor in the air relative to the total amount the air can hold. How much water vapor can the air hold? That depends on temperature.

Front 10

sleet

Back 10

Sleet forms when snow melts as it falls through a layer of warm air and then refreezes. It turns into small, clear ice pellets as it passes through a cold layer near the ground.

Front 11

stratus cloud

Back 11

Stratus clouds occur low in the troposphere. They form in layers that spread horizontally and may cover the entire sky like a thick blanket. Stratus clouds that produce precipitation are called nimbostratus. The prefix nimbo- means “rain.”

Front 12

weather

Back 12

Weather occurs because of unequal heating of the atmosphere. The source of heat is the Sun.Weather refers to the conditions of the atmosphere at a given time and place.

Front 13

air mass

Back 13

ir mass is a large body of air that has about the same conditions throughout

Front 14

anticyclone

Back 14

anticyclone is a system of winds that rotates around a center of high pressure. Anticyclones bring fair, dry weather.

Front 15

cold front

Back 15

cold front occurs when a cold air mass runs into a warm air mass

Front 16

cyclone

Back 16

A cyclone is a system of winds that rotates around a center of low pressure. Cyclones bring cloudy, wet weather.

Front 17

front

Back 17

The boundary between two air masses is called a front

Front 18

occluded front

Back 18

occluded front, a warm air mass becomes trapped between two cold air masses.

Front 19

stationary front

Back 19

Sometimes two air masses stop moving when they meet. These stalled air masses create a stationary front

Front 20

warm front

Back 20

When a warm air mass runs into a cold air mass it creates a warm front

Front 21

blizzard

Back 21

A blizzard is a snow storm that has high winds

Front 22

hurricane

Back 22

hurricane is an enormous storm with high winds and heavy rains.

Front 23

lake-effect snow

Back 23

If they are near a lake, they may be getting lake-effect snow

Front 24

lightning

Back 24

Lightning is a huge release of electricity.