Weather Forecasting
Measuring Weather data:
Humans have long been interested in weather forecasting, the process of predicting future weather based on
ongoing observations of atmospheric conditions.
Even before we had the technology of weather instruments, humans were forecasting weather based on the
behavior of plants and animals, characteristics of the Sun and moon, and cloud formations. We often refer to these
as weather folklore.
Meteorologists measure the components of weather using a variety of instruments and observation systems.
Weather Component
Temperature
Wind speed
Wind direction
Humidity
Air pressure
Precipitation
Instrument
Thermometer
Anemometer
Wind vane
Hygrometer
Barometer
Rain gauge or meter stick
Units
°C
Km/h
Compass direction (NW)
%
kPa
mm and cm
Humidity can drastically affect temperatures or what we refer to as “feels like” temperature. Environment Canada
created what is known as the humidex scale. It takes into account the temperature of the air along with the
humidity and tells us how we will feel on a hot day when the humidity is high. For example, on a day where it is
30°C and the humidity is 95%, the “feels like” temperature will be 47°C. This is because the humidity in the air
prevents the sweat on our skin from evaporating and we cannot cool down.
Before anemometers, humans used what is known as the Beaufort wind scale to describe and determine wind
speed. It is a scale from 0-12 that describes wind based on the behavior of the ocean and objects on land. See
Table 2.1 on page 53 in your text to explore the descriptions on the scale.
Along with weather instruments, meteorologists also use weather observations systems to collect weather data.
They are collectively known as remote sensing technology (RST) because they can collect data without being in
physical contact with the object being observed. These include weather balloons, weather radar and weather
satellites.
Weather Balloon: meteorologists send weather balloons containing a radiosonde into the atmosphere to collect
weather data. It can collect data on temperature, atmospheric pressure, humidity, along with wind speed and
direction. Eventually the balloon will burst and the radiosonde will parachute back to Earth.
Weather Radar: this is very important form of remote sensing technology. It sends out radio waves that reflect
off objects in the atmosphere and its main function is to detect precipitation and storms. The higher the amounts
of precipitation present in the clouds, the greater the amount of reflection. Special radar technology known as
Doppler radar can determine the direction and speed of weather systems, which allow us to predict the behavior of
approaching storms. To see the image created by radar, go to page 55 in your textbook and look at figure 2.16.
Weather Satellites: this remote sensing technology has been launched into orbit around the Earth and they
monitor the behavior of the atmosphere and help us predict and understand the development and movement of
weather systems (i.e., fronts, high pressure & low pressure systems). They use technology such as infrared and
visible light sensors and can determine cloud height and the difference between types of precipitation. We
currently use two types of weather satellites, Geostationary and Polar Operating Environmental Satellites. GOES
orbit the Earth about 36000 km above the equator, travels at the same speed as the Earth rotates and therefore
monitors a fixed location. POES orbit the Earth 14 times per day collecting data from the entire globe. POES collect
data that allow us to track various weather systems.
Forecasting the Weather
Meteorologists can use collected weather data to make short-range forecasts (48hrs) and long-range forecasts (3-7
days). Short range is based on what is known as persistence forecasting. In other words, the assumption that
current weather patterns will continue for a few hours. Meteorologists also use nowcasting, which uses data from
RST and forecasts weather for up to 6 hours.
When data is recorded and forecasts are being made, meteorologists use a variety of weather symbols, which are
displayed on maps to indicate weather conditions. Refer to page 63 in your text to explore some common weather
map symbols. Due to the fact that weather maps show current conditions, they can be used for short term
forecasting. They can look for patterns and trends and make predictions on how the atmosphere will behave.
They watch for systems meeting one another, locations of weather fronts, speed and direction of systems and all
this combines to make a weather forecast.
Long-range weather forecasting is much more difficult and relies on statistical analysis of past weather data and
computer models of atmospheric circulation and behavior. These forecast are often unreliable because the
computers are making assumptions about how the atmosphere will behave but it is one of the most unpredictable
systems on earth!
Importance and Limitations of Weather Forecasting
Weather forecasting is very important to help people prepare for a variety of weather conditions, some of which
can be hazardous to our health, others that can cause unsafe driving conditions, and some that can cause major
property damage. A forecast helps us to make choices daily based on weather conditions. It can be as simple as
what clothing to wear or as complicated as stocking up on food and supplies to prepare for extreme weather.
Weather forecasting can help us prevent loss of life, property damage and even helps us prevent weather related
illnesses such a hyperthermia.
Effects of Weather on Agriculture: There are many, many ways that weather can affect agriculture. It can be a
very dry or overly wet season, and early or late frost or a heavy hailstorm that destroys crops meant for human
consumption. Animals may not survive overly cold or hot seasons. Accurate predictions of weather can help
farmers prepare for these impacts and time their planting, protection and harvesting of crops.
Effects of Weather on Marine Industries: Fishermen and offshore oil workers risk injury and death out on the
ocean daily, due largely in part to weather. Good and reliable weather forecasting is needed to help them make key
decisions about when to go out on the ocean and when they need to come ashore.
Effects of Weather on the Forestry Industry: Almost half of the 9000 forest fires each year in Canada are started
by lightning strikes. Accurate weather forecasting can help us prepare for the possibility of forest fires and prevent
millions of dollars in damage , not to mention the cost to ecosystems, wildlife and the atmosphere will all the excess
carbon dioxide that is released.
Effects of Weather on Transportation: Weather forecasts are essential to help people prepare for travel,
whether it is on roads, over the water or in the air. Bad driving conditions cost us over $1 billion in damage each
year to vehicles and infrastructure. Many flights are cancelled or delayed due to weather conditions in an attempt
to eliminate risk to flight crews and passengers.
The need and importance of weather forecasting is obvious, however we are still limited in what we can predict.
We have minimal control over weather and ultimately the atmosphere is too unpredictable to ever know with
100% accuracy what is going to happen. The good news is that with our improved technology, our current 5-day
predictions are as accurate as our 2 day predictions were 20 years ago.