Answer Key – Chapter 16 – Weather
16.1 Weather and water
1.
2.
3.
4.
5.
Weather refers to conditions of the atmosphere at a given time and place.
Humidity, clouds, precipitation.
Humidity is the amount of water vapor in the air.
Clouds form when water vapor condenses in the air around specs of matter.
Sleet – small clear ice pellets formed when there is an upper cold layer that forms snow then a
shallow warm layer where the snow melts and finally near the surface a cold layer that refreezes
the water.
Freezing rain- liquid water, freezes on the ground, formed when there is a cold layer that forms
snow, then a large (deep) warm layer to melt the snow, then a shallow cold layer near the
surface to freeze the liquid on surfaces.
Hail – balls of ice, formed when there are strong updrafts that carry rain high into the
troposphere where it is cold and the ice is formed, the size depends upon how often the ball of
ice gets carried back up and multiple layers form.
6. Cirrus (wispy), stratus (layers), cumulus (puffy)
7. Dew point-the point (temperature) at which water will condense out of the air as dew, it
happens at 100% humidity
8. At night the air cools, the cooler air cannot hold as much water vapor so the water condenses
on surfaces in the form of dew.
9. Hail is a form of precipitation and therefore forms in a cloud that produces precipitation (a
stratus or cumulus) it must also form high in the troposphere where it is very cold, the most
likely candidate is therefore the cumulonimbus cloud.
16.2 Changing Weather
1. An air mass is a large body of air that has about the same conditions throughout.
2. A continental polar air mass forms over cold (polar) land (continental) so the mass is cold and
dry. A maritime tropical air mass forms over warm (tropical) water (maritime) so it is a warm
moist air mass.
3. Air masses move because of wind (which is caused by unequal heating and therefore pressure)
and the particular wind called the jet stream. The coriolis effect causes them to move on a
diagonal.
4. A front is the boundary between two air masses.
5. A cyclone is winds rotating around a center of low pressure. An anticyclone is winds rotating
around a center of high pressure.
6. Your picture of an occluded front should be similar to figure 16.9. The weather conditions along
the front should show clouds above and precipitation along the front.
7. Warm and cold fronts are similar: they are the boundary of an air mass, the differences in
temperature and pressure cause clouds and precipitation. Warm and cold fronts are different:
cold fronts occur when cold air runs into warm air (vice-versa for warm), cold fronts move cold
air under warm air (warm move warm air up over cold air), weather is cool after a cold front
moves through (warm after a warm front moves through).
8. The weather tomorrow will be rainy, a stationary front does not move very quickly so the
weather will not change.
16.3 Storms
1. Storms are episodes of severe weather. Three types of storms are: thunderstorms, tornadoes,
and hurricanes (and blizzards).
2. Thunderstorms occur because warm humid air rises rapidly creating strong updrafts and
cumulonimbus clouds called thunderheads, the cool air cannot hold all the moisture so
precipitation occurs.
3. Lightning is a huge release of electricity. It occurs because some parts of the thunder cloud are
negatively charged and others positive, the charge difference creates lightening.
4. Tornado alley is a north/south area in the US where the greatest number of tornadoes occur.
There are many tornadoes there because it is where warm air masses from the south run into
cold air masses from the north.
5. Hurricanes form over warm ocean water from tropical cyclones, it is an enormous storm with
high winds and heavy rains. They get their energy from the warm water.
6. Because the damage includes missing roofs on the house the tornado could be classified as an
F2.
7. The graph plots number of storms per 100 years versus date during the hurricane season, May
through December. The graph shows that the most storms occur in the middle of September.
The orange and yellow colors show that hurricanes (yellow) are a fairly constant percent of total
tropical storms, the yellow graph follows the same contour as the orange.
8. The northern plains part of the US is most likely to have blizzards because blizzards must have
blowing (plains have strong wind) snow.
9. Lake effect snow storms occur on the east side of lakes in the US because weather moves from
west to east and as the front moves over the lake it picks up moisture, the difference in
temperature from the warmer winter water to cold winter land (remember water takes longer
to cool than land) causes the air to cool down and therefore lose its moisture.
16.4 Weather Forecasting
1. Weather is difficult to predict because there are so many factors involved and slight changes
may make a big weather change.
2. Thermometer measures temperature, anemometer measures wind speed, rain gauges measure
how much rain has fallen, hygrometers measure humidity, wind vanes show wind direction,
snow gauges show how much snow has fallen, barometers measure air pressure.
3. Weather balloons and weather satellites gather data such as those mentioned in question #2.
4. A weather map shows
5. Isobars are lines of equal pressure, isotherms are lines of equal temperature.
Website activity
1. Clear areas on a satellite image indicate no clouds and therefore sinking air. Cool air sinking and
warming up does not produce clouds.
2. The air around an area of high pressure moves clockwise.
3. The air around an area of low pressure moves counterclockwise.
4. A cold front occurs when a cold air mass moves and encounters a warm air mass, they do not
mix and the boundary is called a cold front. It is a blue line with triangles on a weather map. The
cold air will move under the warm and lift the warm air up. The weather following a cold front
moving through will therefore be cool.
5. A warm front occurs when a warm air mass moves and encounters a cold air mass, they do not
mix and the boundary is called a warm front. It is a red line with rounded ‘bumps’. The warm air
will lift up over the cold air. The weather following a warm front moving through will be warm.
6. False The wind direction flag on a station weather plot points in the direction that the wind is
blowing from.
7. The sky is overcast or 100% cloudy if the station weather plot is completely filled in.