Fire season and firestorms

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Fire season and firestorms

There are roughly 8,000 wildfires in Canada each year. Fire weather refers to weather conditions that are conducive to fire. These conditions determine the fire season, which is the annual period(s) of the year during which fires are likely to start, spread, and cause sufficient damage to warrant organized fire suppression.

The grayish-brown swirl billowing over the northern Prairie Provinces is smoke that had risen from the Fort McMurray, AB fire complex on May 17, 2016. Actively burning areas, fires, are shown as red dots. Credit: NASA Goddard MODIS Rapid Response Team.

The length of the fire season

Start of fire season – For regions that receive significant snow cover during the winter (i.e., more than 10 cm, with snow cover present at least 75% of the days in January and February), start-up of the fire season occurs when the area has been snow-free for three consecutive days, with noon temperatures of at least 12°C. For regions that do not report significant snow cover during the winter, start-up occurs when the mean daily temperature has been 6°C or higher for three consecutive days.

End of fire season – The fire season ends with the onset of winter, generally following seven consecutive days of snow cover. If there is no snow data, shutdown occurs following seven consecutive days with noon temperatures lower than or equal to 5 °C.

What is a firestorm?

Possibly the most dangerous type of weather associated with a forest fire is when a pyrocumulonimbus storm cloud is generated.