5.8A Weather & Climate
Key Concept 1: Weather refers to the daily environmental conditions
we experience around us.
It is also used to describe the condition of the atmosphere in a place at a
certain time. Weather describes the daily condition of the air outdoors,
such as temperature, cloud cover, wind speed, humidity (amount of water
vapor in the air), and precipitation (rain, hail, sleet, or snow). All weather is
caused by the Sun heating Earth unevenly, creating high and low pressure
air masses (pressure is the weight of the air) that interact and bring fair or
stormy weather. Seasonal changes in weather are also caused by uneven
heating of Earth’s surface, which receives varying amounts of direct and
indirect sunlight due to the tilt of Earth as it revolves around the Sun.
Low-pressure air masses generally bring stormy weather. This occurs
because the air is warm and rises where it meets cooler air. This cooling
causes the water vapor to condense and form clouds, and storms may
appear. Lower pressure air masses vary in intensity with some bringing
gentle rain, and others bringing blizzards, violent thunderstorms, or
hurricanes.
High-pressure air masses have heavy cold air that sinks. The descending
air warms up causing clouds to dissipate, which brings clear skies and fair
weather. The movement and interaction of these high and low pressure
air masses is used to forecast the weather.
Students will use Fahrenheit temperature scales to interpret temperature
trends among several cities. Remind students that the Celsius ©
temperature scale in previous modules uses 0 degrees for the point that
water freezes and 100 degrees for the boiling point. Weather maps in the
United States use the Fahrenheit (F) temperature scale where 32 degrees
is freezing and 212 degrees is boiling.
Key Concept 2: Climate refers to the average conditions in a place
over a longer period of time.
When weather data trends are analyzed over a 30-year period,
generalizations about climate conditions for that region can be inferred.
The difference between weather and climate is the period of time
analyzed. Short term daily, weekly, monthly and yearly data refers to
weather. Long-term data averaged over 30 years refers to climate.
Averaged over 30-years means the weather data for a particular city was
added up for that period of time and divided by the total number of data
entries used. For example, if the July monthly temperature data for a city
during a 30 year period added up to be 2700 degrees, dividing that by 30
years results in an average temperature of 90 degrees for the month of
July. That is a fairly hot temperature average, and you could generalize
that city had a hot summer climate.
Global climate zones exist around the world. Not only do cities around
the world have climate patterns, but average conditions of the
atmosphere over long periods of time are found globally. Earth is divided
into distinct climate zones that are created by global circulation patterns.
The tropics are the warmest, wettest regions of the globe, while
subtropical high-pressure zones create dry zones at about 30° latitude
north and south. Temperatures and precipitation are lowest at the poles
due to year round cold dry air.
Key Concept 3: Weather can be observed each day, whereas climate
must be observed over time.
This concept re-emphasizes the difference between weather and climate.
As an example, the climate of the Southeast Gulf Coast of the United
States would be described as near tropical, warm, and humid. However,
on any particular day, the weather may be cold and icy, but the
description of the overall climate would still be tropical. Students have the
opportunity to apply this knowledge in the exploration activity where they
differentiate weather and climate data for six cities, find trends, and make
generalizations about which climate data best matches the description of
that city.