Weather Forecasting Technology
History of Weather Forecasting
Humans have always attempted to predict the weather. In 650 BC, people living in
Babylonia, an ancient state in the southern part of Mesopotamia (modern day Iraq), predicted
the weather from cloud patterns. The ancient Chinese predicted the weather by observing
patterns of events. If the sunset was unusually red, it was often an indication of good weather
for the following day. Although these ancient methods of weather forecasting were used for
centuries, they were not always reliable. Another limitation was that information about the
current state of the weather could not be communicated to places far away. So, if a
community of Babylonians were experiencing a terrible storm, they had no way to warn their
neighbors downwind that trouble was coming!
The most basic weather forecasting is still based on the observation of weather
patterns, which over the years has led to folklore about the weather (see the Pre-Lesson
Assessment section). You are probably familiar with Groundhog Day, celebrated on February
2 in the US. This folklore originated from ancient Celtic people who believed that if the
winter's midpoint was sunny and clear, a long, cold winter would follow. Today, people
celebrate this day with a groundhog named Punxsutawney Phil, who resides in Philadelphia.
The tradition is that every year, on the morning of February 2, Punxsutawney Phil leaves his
home under the ground. If it is sunny and clear enough for little Punxsutawney Phil to "see his
shadow," a long winter is predicted. Unfortunately, this weather folklore is only accurate about
half the time!
Modern Forecasting Equipment
Today, we rely on modern forecasting
technology and engineering to predict weather
patterns. The modern age of weather forecasting
began with the invention of the telegraph in 1837,
which allowed forecasts to be made by knowing
the actual weather conditions in distant places.
Even more progress was achieved during
the 20th century when engineers and scientists
designed computers to make numerical weather
predictions (computer simulations) of the
atmosphere (see Figure 2). These simulations take
information about the present weather and use the
computational tools of physics and fluid dynamics
to predict future atmospheric states. Basically, the
complicated equations used by the computer
project how the working fluids of the atmosphere
(that is, wind and water) are expected to change
Figure 2. Pilots depend on computer-simulated
with different atmospheric conditions (that is,
models of weather objects and terrain features to fly
temperature, humidity and pressure).
planes safely.
It is important to note that before any fancy
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computer simulations can be made, "raw" weather
data (actual weather measurements) must be collected.
Weather Balloons
Weathers balloons carry instruments high
up into the atmosphere. The balloons, launched
every day all over the world, carry a radiosonde
high up into the atmosphere. The radiosonde is
a small, battery powered device that collects
information about atmospheric pressure,
humidity, and temperature. These data are then
transmitted to a ground antenna via specific
radio frequencies. Wind speed and direction are
calculated by tracking the weather balloon using
GPS or radio direction finding. The flight of a
weather balloon doesn't last very long. The
weather balloon is filled with either helium or
hydrogen, which lifts the device into the
atmosphere at a rate of about 1000 feet per
minute. In its flight, the weather balloon can
ascend to over 35 km (115,000 feet) and drift
more than 300 km (about 180 miles) from where
it was launched. As the balloon ascends, the
pressure decreases, which causes the balloon
to expand from an initial diameter of 1.5 feet to
6-8 feet. Eventually the balloon expands so
much that it ruptures. The radiosonde has a
Figure 3. Weather balloons are launched every day
parachute attached to it so that it is less likely to
around the world to collect data from the atmosphere.
cause damage when it returns to earth. Most
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radiosondes are not found after they return to
earth. Of the approximately 70,000 radiosondes deployed every year, only about 20% are
found and returned to the National Weather Service for reconditioning and reuse.
Satellite Technology
What about the big picture? Weather satellites are another engineering marvel that enable us
to see what the Earth and clouds look like from space and give us a more comprehensive
view of Earth's interrelated systems and climate. Figure 4 was created using data from four
different satellites. The red dots you see are fires burning on land areas, and the large aerosol
clouds over the Atlantic Ocean are from the burning of biomass in Africa. You can also see
dust and clouds wrapped around the planet.
Figure 4. A satellite image of Earth.
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Weather Radars
What if we wanted to see inside a large cloud or storm to analyze its structure and
gauge its potential to cause severe weather? Is this possible? Military radar operators asked
this same question during World War II, when they noticed noise in returned radar echoes
due to weather elements such as rain, snow and sleet. When the war was over, many of
these military radar operators became engineers to develop a use for the noisy echoes. Now,
we have weather radar, a special type of radar that uses radio waves to "see" how
precipitation is behaving in a cloud and how it might change.
Figure 5. All weather radars work by the process of scattering.
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RADAR stands for radio detection and ranging. Basically, a radar is an electronic
instrument used to determine the direction and distance of objects that reflect radio energy
back to the radar site. Weather radars use radio waves to locate precipitation and determine
its type (rain, snow, sleet or hail). They also calculate the motion of precipitation and forecast
its future position and intensity.
All weather radars work by the process of scattering, in which radiation energy is
reflected by small particles, as shown in Figure 5. So, when weather radar sends a radar
beam out into space, the precipitation particles in the atmosphere cause the radiation energy
to scatter. The motion and behavior of the scattered radiation is read by the radar site and
translated into important weather information.
The Doppler Radar
Most weather radars
are Doppler radars, which can also detect
the motion of rain droplets. Doppler radar
gets its name from the Doppler effect.
Have you ever listened to an ambulance
siren or a train whistle as it was coming
toward you? You probably noticed that the
pitch of the whistle changed as the train
passed you and moved away. This change
in the frequency of sound is called the
Doppler effect.
A Doppler radar measures the
changes in the frequency of the signal it
receives to detect the intensity of
precipitation, estimate wind direction and
speed, and predict hail size and rainfall
amounts. Doppler radar gives forecasters
Figure 6. Doppler radar used by the U.S. National Weather
the capability of providing early detection
Service in Sioux Falls, Minnesota.
of severe thunderstorms that may bring
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strong damaging winds, large hail, heavy
rain and possibly tornadoes. Figure 7 shows the radar reflectivity image of the Oklahoma
City/Twin Lakes Doppler radar taken on May 8, 2003, just before a tornado hit the General
Motors plant in the area. Because the Doppler radar (shown is the early formation of the
tornado) provided the NOAA National Weather Service with 30 minutes advance warning,
officials were able to move the 1,200 employees to a shelter before the tornado hit.
Figure 7. Doppler radars give us advance warning of natural
hazards, such as tornadoes.
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Who Uses the Information?
We can certainly appreciate the staggering advances in weather forecasting equipment
since the telegraph was used 100 years ago. What about the people who use the equipment?
Who looks at all this weather data? Who checks to see if it makes sense?
One international organization is the World Meteorological Organization (WMO), an
agency of the United Nations. WMO works to verify and standardize weather data and make it
available to national meteorologists, local forecasters and other people interested in weather
science and forecasting. This weather data is then put into maps by computers, which can
make forecasts based on certain conditions and mark them on weather maps. Then, it is the
meteorologist's job to read and interpret these maps to make forecasts about the weather.
You can obtain daily weather information for your city from the World Meteorological
Organization by visiting http://worldweather.wmo.int/.
It is interesting to note that, according to NASA, the US statistically has the world's
most violent weather. In a typical year, the US endures about 10,000 violent thunderstorms,
5,000 floods, 1,000 tornadoes, and several hurricanes. For this reason, improving weather
prediction has been a high priority of meteorologists for a very long time. Engineers and
scientists continue to work to improve weather forecasting technology to provide more
accurate weather forecasts for the benefit of society, the economy and the environment.