How did this deadly Alberta fire spread so fast?

One kilometre in just 36 seconds. That's how fast military officials say a grass fire travelled at CFB Wainwright in Alberta on Saturday, where four soldiers were killed and dozens more injured. That's the equivalent of 100 kilometres an hour, an extraordinary speed even for a grass fire. But the weather observations from that afternoon show just how dramatically conditions were changing. Take a look at this. A powerful cold front was sweeping across Alberta. Between 2 and 3 p.m., winds were blowing from the southwest, gusting to around 46 kilometers per hour. But by 4 p.m., temperatures dropped 10 degrees, a clear sign of the frontal passage as cold air swept in. The winds swung around to the northwest, a roughly 90-degree change, and suddenly got much stronger, with gusts approaching 70 kilometers per hour. But those were just the recorded winds at the weather station. Gusts over 90 kilometers per hour in between those observations were highly likely. This change in wind direction and speed was forecasted. Environment and Climate Change Canada had issued a wind warning for parts of Alberta in advance of that cold front. As for the fire, satellite imagery did show a fire burning in the area earlier that afternoon. Wind-driven grass fires are not uncommon on the prairies. And while cold fronts are also a regular feature, the sudden changes in wind speed and direction they bring can dramatically change fire behaviour. And dry vegetation is part of the picture too. Fire danger at the time was high to extreme and many parts of the province have experienced prolonged drought in recent years, although local conditions still need to be established. Grass is a fine fuel that can dry out quickly, ignite easily and carry flames across open landscapes at high speeds. A sudden shift in wind direction can make things even more complicated. A fire spreading in one direction can suddenly have its entire flank exposed to the wind and what was a side of the fire can become a rapidly advancing front in moments. We can't say for certain how these conditions shaped the incident at CFB Wainwright, but a major investigation is now underway into what other factors may have contributed during the military training exercise.