Backgrounders on various weather services: chapter 2

One-to-Seven-Day Weather Forecasts

With such a vast country full of defining seasons, it is no wonder that Canadians are often known for being weather obsessed. This is also likely why Environment Canada’s (EC) main forecasting website, receives an average of 50 million visits a month, making it one of the most popular websites in Canada. Despite the relative ease with which we access weather information, the science behind EC’s popular one-to-seven-day weather forecasts is more complex.

Weather forecasters use science and technology to predict the state of the atmosphere at a future time for a given location.
A daily weather forecast provides:

  • Weather alerts, if in effect
  • Temperature
  • Precipitation, including type, probability of and amounts
  • Wind, including speed and direction
  • Fog and other obstructions to visibility
  • Wind chill and Humidex, if appropriate
  • UV Index
  • Air Quality Health Index (for certain communities across the country)

In a seven-day forecast, forecasts for the first two days are expressed as a relatively detailed sequence of expected weather events. Days three to seven are usually listed in a more general sense, focusing on the most significant expected weather for each day.

Environment Canada’s Meteorological Service of Canada plays a very important role in providing the country with its weather forecasts and is the official provider of Canada’s weather alerts (warnings, watches, advisories and special weather statements).

Severe weather warnings, watches and special weather statements alert Canadians to current or expected weather conditions that could impact their safety and their property. It is EC’s goal to ensure that all Canadians know about potential severe weather impacts well in advance.

How are weather forecasts made?

EC’s weather forecasts and alerts are produced using technology, including satellites, Doppler radars, a powerful supercomputer, new forecaster workstations and a greater use of weather information received from the general public.

Step 1

The first step in forecasting the weather involves an analysis of the state of the atmosphere. EC collects data daily from thousands of weather monitoring sites across the country and the world.

Step 2

All the data collected are analyzed and used in EC’s numerical weather prediction models. These models are essentially the mathematical representations of what is present in the atmosphere. This process is done through the use of EC’s supercomputer.

Step 3

Current observations and the numerical model output are used by meteorologists in the analysis and diagnosis of current weather conditions. The meteorologists pay special attention to possible severe weather in the upcoming two days, and will issue severe weather alerts as appropriate. Forecasts are disseminated out to Canadians through EC’s Weather website, Weatheradio, automated telephone answering devices, to the media and for display on numerous weather websites in Canada.

For more information on the science behind weather forecasting, and EC’s one-to-seven-day forecasts visit:

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