Monday, May 9, 2016

Ingredients for a Wildfire - Fort McMurray, Alberta

The Fort McMurray fire in Alberta, Canada ignited sometime on May 1, very likely human-caused. It was quickly news on social media, but it was a couple of days before it was widely reported in the news. Spectacular video taken by evacuees quickly went viral on the Internet.

The spring fire season in the boreal forests in British Columbia and Alberta got off to an early start this year. A dry winter and early spring was one of the main factors.

This map shows the status of drought across Canada. Higher values indicate drier conditions

The very warm spring resulted in a faster than normal spring melt. In a normal spring the snow melts gradually keeping the forest floor moist. With the warm dry winter the forest floor was covered in dry leaves and pine needles. The premature spring warmth and low humidity dried things out even further.Deciduous trees, such as aspens, hadn't yet sprouted leaves. Leaves transpire moisture into the forest and help cool the forest environment.

The end of April and early May was unseasonably hot. The maximum temperature last Wednesday (May 4) in Ft. McMurray reached 91°F (32.6°C), with the humidity about 15 percent. Ft. McMurray is located at 56.6° North, about the same latitude as the Aleutian Islands. Several dozen Canadian record high temperatures were set that day. The hot weather last week was caused by an upper ridge of high pressure that extended through western Canada and into the Arctic Circle. High temperatures reached the 80s to low 90s from the Dakotas north through Alberta and Saskatchewan.

500 millibar map for Wednesday, May 4, 2016

With plenty of tinder dry fuel, hot dry weather, and strong winds it was no surprise the Fort McMurray fire took off like it did. It was far from the first fire of the season. Fire activity across British Columbia and Alberta was already well above average.

Number of Canadian wildfires by province in 2016 compared to normal

The Fort McMurray fire was intense and produced smoke that turned day into night. It also generated pyrocumulus clouds with lightning.

This video gives you a sense of what it was like evacuating from Ft. McMurray. It's both frightening and mesmerizing. Note that this was recorded during the middle of the afternoon.

This animation shows the extent of the Fort McMurray fire as it spread over the past nine days. As of today the extent of the area affected by the fire was more than 200,000 hectacres (2000 sq km). The good news is that latest reports indicate that about 85 to 90 percent of the structures in Fort McMurray were saved. Unfortunately, neighborhoods in the path of the fire, such as Beacon Hill in the video above, were largely destroyed. It's estimated that the fire destroyed 2,400 structures.

The fire danger last week across most of Alberta and southern Saskatchewan was Extreme.

Fire Danger across Canada on May 5, 2016

Conditions improved yesterday and last night as cooler weather and rain fell across the province.

Fire Danger on May 9, 2016

Amounts were light (5 to 10 mm, about 0.25 to 0.30 inch) but most welcome. One CoCoRaHS location on the Alberta/NWT border (CAN-NT-7) reported 34.3 mm (1.35 in.) of rain indicating a "steady cold rain all day and evening".

Wildland fire activity in Alberta has been well above average the last three years and is well on its way to another above average year. Last year fires burned 491,000 hectacres of land, well over twice the ten-year average of 179,000 hectacres. The Fort McMurray fire alone has already exceeded the average.