Chapter 16 Section 4:
Forecasting the Weather
At some point in your life, you have been caught off guard by the weather. Weather can
affect what you wear and what you do outside, so it can be important to get the weather forecast.
A weather forecast is a prediction of future weather conditions over the next 3 to 5 days.
Meteorologists factor in recent weather as well as observe and collect the current conditions in
order to make the predictions. In order to collect the current conditions outside, meteorologists
make a number of measurements.
Temperature:
A thermometer is a tool used to measure the air temperature. A common type uses a liquid
sealed in a narrow glass tube. When the temperature increases, the liquid expands up the tube.
When the temperature decreases, the liquids shrinks and moves down the tube. Globally,
temperature is given in degrees Celsius. In the U.S., however, temperature is generally reported
on the TV and radio in degrees Fahrenheit.
Pressure:
A barometer is an instrument used to measure the air pressure. A mercury
filled barometer is the most accurate. A barometer consists of a glass tube open
at one end. It is placed upside down in a container of mercury. Some of the
mercury drains out of the tube, but the air pressure, pushing down on the
mercury in the container, causes much of the mercury to stop draining out. The
greater the air pressure pushing on the container of mercury, the more the
mercury will stay in the tube. Scientists measure the height of the mercury in
the tube. In the U.S, barometric pressure is reported in inches of mercury.
Wind direction:
Wind direction is measured using a wind vane or
wind sock. It is a cone-shaped cloth bag open at both ends
attached to a pole. The wind enters the bag through the wide end and leaves
through the narrow end. Therefore, the wide end points into the wind.
A wind vane is shaped like an arrow with a large tail at one end,
attached to a pole. The wind pushes the tail, spinning it on the pole until the
arrow points into the wind.
Barometer
Wind Speed:
Wind speed is measured with a device called an anemometer. It
consists of three or four cups connected by spikes to a pole. The wind
pushes on the hollow sides of the cups, causing them to rotate on the pole.
The faster the wind, the faster the rotation.
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Wind sock
Measuring conditions in the upper atmosphere:
Studying the weather at higher altitudes requires more complicated equipment. Weather
balloons are sent up with equipment to measure and transmit conditions back to operators on the
ground. Radar is also used to find the location, type, movement, and intensity of precipitation and
storms. Satellites orbiting the Earth also provide images and can measure wind speeds, humidity,
and temperatures and various altitudes.
The National Weather Service (NWS) collects, analyzes,
and reports the conditions. They make maps based on
information gathered from over 1,000 weather stations across
the U.S. On these maps, each station is represented by a small
circle or station model. The circle includes a set of symbols and
numbers surrounding it, which represents its weather data.
Weather maps also include lines called isobars that connect
points on the map with equal air pressure. Isobar lines that form closed
loops represent areas of high and low pressure. These areas are usually
marked with a capital H or L . Fronts are also symbolized on the maps.
Questions Section 16-4: Answer the following questions searching the reading assignment above.
__________1. A weather _____ is a prediction of future weather conditions.
__________2. A ______ is an instrument used to measure the air pressure.
__________3. A ______ is a tool used to measure the air temperature.
__________4. Temperature is generally reported on the TV and radio in degrees ______.
__________5. Barometric pressure is reported in ____ of mercury.
__________6. The _____ the air pressure pushing on the container of mercury, the more the
mercury will stay in the barometer tube.
__________7. When the temperature increases, the liquid ____ up the thermometer tube.
__________8. Wind direction is measured using a wind vane or wind ____ .
__________9. The wind pushes the tail of the wind vane, spinning it on the pole until the arrow
points ___ the wind.
__________10. Lines called _____ connect points on the map with equal air pressure.
__________11. Wind speed is measured with a device called an _______.
__________12. _____ orbiting the Earth also provide images and can make measurements.
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