Weather Review
Nearly all the atmosphere is confined to a thin shell surrounding the earth. The atmosphere is a
mixture of gases.
79% nitrogen
1.
2.
3.
4.
20% oxygen
1% other (carbon dioxide, water vapor)
Provides oxygen and needed gases
Creates livable conditions
Provides water
Protects us from radiation and meteorites
As altitude increases, air pressure decreases.
Weather describes the conditions of the atmosphere at a given location for a short period of time.
Troposphere- all weather occurs in the layer of the atmosphere that is closest to the earth
Weather is the result of the uneven heating of the Earth’s surface.
Substances enter the atmosphere naturally and from human activity...these substances can affect
weather, climate, and living things.
Pollution: Adding extra gases to the atmosphere can lead to future problems.
Natural: forest fires and volcanic eruptions can add dust, ash, and smoke to the earth’s atmosphere. This
could influence the weather and climate in affected locations.
Human: Increased greenhouse gases, such as carbon dioxide, can increase the temperature on earth which
some scientists believe will lead to the melting of the polar ice caps.
The sun is the major source of energy for Earth. The water cycle is caused by the energy from the
sun.
Climate is the characteristic weather that prevails from season to season and year to year.
Water circulates through the atmosphere, lithosphere and hydrosphere in what is known as the water
cycle.





evaporation water vapor enters the atmosphere
condensation water vapor molecules turn back into liquid and form clouds
precipitation water droplets become too heavy and fall to earth as rain, snow, sleet, or hail
runoff water moves along the earth’s surface and heads to areas of collection
collection water collects in lakes, streams, oceans, rivers, ponds, etc.
Air masses form when air remains nearly stationary and takes on the conditions from that location.
tropical (forms at equator) polar (forms at poles) maritime (forms over ocean) continental (forms over land)
warm
cold
moist/wet
dry
Most local weather conditions changes are caused by the movement of air masses.
High pressure usually brings fair weather
Low pressure usually brings cloudy, unstable conditions
The movement of air masses is determined by prevailing winds and upper air currents.
jet stream- a current of strong winds concentrated in the upper troposphere
Air masses usually move from west to east in the U.S.
Fronts are boundaries between air masses. Precipitation is likely to occur at those boundaries.
cold front- leading edge of a cold air mass
warm front- leading edge of a warm air mass
stationary front- a front that stays in one place for some time
Precipitation will occur at all
fronts. The type of
precipitation will be
determined by the air
temperature.
occluded front- cold front overtakes a warm front
Hazardous weather conditions include thunderstorms, tornadoes, hurricanes, ice storms, and
blizzards.
tornado- a violently rotating column of air
hurricane- a tropical cyclone with winds of at least 74 mph
blizzard- a condition with low temperatures, high winds, and heavy snowfall with blowing and drifting