Download Tools We Use for Weather Prediction

Predicting Weather
Meteorologists are scientists who monitor weather conditions. They sample a wide network
of weather stations and use satellite images to map out the positions of the large air masses
circling the Earth. Since air masses interact in a relatively predictable way, meteorologists are
able to predict weather patterns with some degree of accuracy.
As explained above, Fronts are responsible for most changes in weather. They occur when a
large mass of cold air meets a large mass of warm air. The front is the zone along which the
masses come into contact with each other. Cold Fronts occur when a cold air mass, which has a
high density, pushes under a warm air mass. The warm air is pushed upward at a sharp angle,
causing moisture to condense rapidly. Heavy precipitation is often the result. Warm Fronts
occur when a mass of warm air passes over a mass of cold air at a moderate angle.
Geography - While fronts indicate the character of prevailing weather systems, local weather
is greatly influenced by geography.
Every weather prediction is based on the chance that the weather conditions will act together
in a certain way. However, forecasts can be wrong. Some general patterns help meteorologists
predict weather for a local area.
Most weather conditions across the United States move from west to east. Moving weather
conditions are due to wind patterns across the earth. In any given place, a clue to tomorrow's
weather may be found by looking at the weather of the area to the west.
However, geographic features in your area such as large bodies of water and mountains can
affect local weather. For example, if you live near the Atlantic Ocean, conditions to the east
often influence your weather. And whether you live near the east coast or west coast,
temperatures near the ocean may be higher than they are even short distances inland. The
heat-holding ability of large bodies of water causes warming of the air along the coast. In a city
such as Chicago, which is located on Lake Michigan, forecasters often give two sets of
information: one for people living within 5-10 miles of the lake, and the second for people in
outlying areas. In the spring, for example, it's generally warmer in the outlying areas than it is
closer to the lake.
People who live on the eastern side of a mountain range such as the Sierra Nevadas have
mostly dry weather. Even when moisture-laden air masses move into the area, their interaction
with the mountains causes most of the moisture to fall on the western slopes.
So keep in mind that you can't just look at a weather map and expect to make totally accurate
predictions. Lots of factors affect what happens in an area on any given day.
For geography, remember these five points:
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coastal areas have more moderate temperatures than inland areas, and are generally
warmer in the winter and cooler in the summer.
in hilly areas, hot air moves up the slopes during the day and down the slopes at night.
high altitude areas are usually colder and receive more precipitation than low altitude
areas.
the air above cities is often warmer than the surrounding area. In certain situations, this
can create an artificial low pressure system.
in coastal areas, cool air usually blows inland during the day and out to sea at night.
Tools We Use for Weather Prediction
While the National Weather Service uses sophisticated equipment such as Doppler radar and
high-altitude balloons to collect data, you can use many of the same tools they use.
Barometer
Barometers measure the air pressure, which is sometimes referred to as barometric pressure.
The pressure of the air on the pool of mercury in the barometer causes the mercury to rise in a
tube. We measure the height of mercury in the tube in inches. Therefore, air pressure is often
stated in inches of mercury.
More common are anaeroid barometers, which don't contain mercury but have a small box
inside instead. The air pressure on this box causes it to change shape, moving a needle on a
gauge that indicates the air pressure. Normal air pressure readings vary from 28 to 31. Quick
changes in air pressure often mean a change in the weather is about to occur. That's why you'll
often hear and read about barometric pressure during local weather reports.
Anemometer
Meteorologists use anemometers to measure wind speed, but you can estimate wind speed
just by looking around. Watch how smoke rises in chimneys, how leaves move in trees, and how
flags wave in the wind. Sailors and other people sometimes rate their observations of wind
speed according to the Beaufort scale.
If you don't have an anemometer to measure wind speeds, you can get a good idea of how fast
the wind is blowing just by looking at objects around you. In 1805, the British Admiral Sir
Francis Beaufort devised an observation scale for measuring winds at sea. The Beaufort Scale
measures winds by observing their effects on sailing ships and waves. Beaufort's scale was later
adapted for use on land and is still used today by many weather stations.
Look at the diagrams below. Each represents one level on the Beaufort scale.
Compare the two pictures below of winds at different speeds on water with the Beaufort scale.
Wind Vane
While anemometers measure how fast the wind is blowing, wind vanes tell you from which
direction the wind is blowing. And knowing where the wind is coming from might give you clues
to the temperature and the amount of water in the air moving into an area. For example, winds
from the south are often warmer and carry more moisture than winds from the north.
Psychrometer
Psychrometers, or wet bulb thermometers, measure relative humidity. A psychrometer uses
two thermometers, one bulb of which is covered with a wet cloth. As the cloth dries, the
cooling effect of evaporation lowers the temperature on that thermometer. Then the
temperatures on the two thermometers are compared on a special chart to find the relative
humidity. Often, the relative humidity is the weather condition that makes people the most
uncomfortable.
Thermometer
Thermometers measure the air temperature via the expansion or contraction of a liquid or a
metal as the air temperature changes. Some thermometers contain red-colored alcohol, others
contain mercury, while still others have a bimetal coil attached to a gauge.
In the United States, temperature is measured using two scales, both of which are based on the
state of water at sea level. Most people use the Fahrenheit scale, on which water freezes at 32
degrees and boils at 212 degrees. Scientists and other people who regularly use metric
measurements measure temperature on the Celsius scale, on which water freezes at 0 degrees
and boils at 100 degrees.
Rain Gauge
Rain gauges are very simple instruments used to measure the amount of liquid precipitation.
Any open container with a flat bottom and straight sides will work just by adding a scale of
inches to it. Other kinds of precipitation are usually recorded by collecting the precipitation in a
similar instrument, then letting the precipitation melt to find out the liquid equivalent. But at
home, you might just want to use a ruler or yardstick to measure a deep snowfall! Then you can
use the average conversion of 10 inches of snow equals 1 inch of rain to find out how much
water fell.