As tens of thousands of residents flee from Fort McMurray, Alta., the threat of more fires continues to loom across Alberta and Saskatchewan.

Wildfire update: Alberta declares a provincial state of emergency: <a href="https://t.co/VZEKzUzfdV">https://t.co/VZEKzUzfdV</a> | <a href="https://twitter.com/hashtag/ymmfire?src=hash">#ymmfire</a> <a href="https://twitter.com/hashtag/ymm?src=hash">#ymm</a> <a href="https://twitter.com/hashtag/FortMacFire?src=hash">#FortMacFire</a> —@YourAlberta

On May 4, Natural Resources Canada indicated that the risk of fire is "extreme" in the two provinces.

A map the federal department produced for Wednesday shows a huge red zone over most of the region.

The Canadian Wildland Fire Information System is a computer-based system that monitors fire danger conditions across Canada.

The system creates a fire danger map based on daily weather conditions such as temperature and humidity.

It also takes into consideration factors like how easy it is to ignite vegetation, how difficult a fire may be to control, and how much damage a fire can do.

Here's what the fire risk map for Western Canada looked like a week ago. Almost nowhere in Saskatchewan was the risk considered "extreme." (Natural Resources Canada)

1 week ago

Last week, fire danger was rated as "low" in places now consumed by fire, like Fort McMurray.

In Saskatchewan, there was virtually nowhere in the "extreme" risk zone.

This time last year

On May 4, 2015, the fire danger map indicated varying risk levels, with the majority of the provinces sitting at "low" to "moderate" risk.

In Saskatchewan, the "extreme" risk zone was limited to the extreme southwest and southern regions. This was before a record-breaking summer in Saskatchewan for wildfires.

A year ago, on May 4, 2015, the fire weather risk was rated as extreme in southwest Saskatchewan, while the north was moderate or low. (Natural Resources Canada)