Thoughts on the wildfire situation in Fort McMurray

Just some thoughts from a former AB gov't wildland firefighter...

Conditions pretty much cannot get worse than this for Alberta. This afternoon, temperatures soared to over 32C, with very low RH values in the mid teens. When the RH is lower than the temperature, we call this "crossover", which aids in intense fire behaviour - especially when the fuel source is tinder dry. When winds are high (this afternoon roughly 20 gusting 40km/h), fire growth occurs rapidly. The peak burning period is typically near 5PM during the warmest time of day when RH is also lowest. A worst case scenario is one like today's, when an out of control wildfire is being fanned by the wind directly toward populated areas.

Wildfires are actioned according to their priority, so those that threaten human life, communities, watersheds and soils, infrastructure, etc get more resources thrown at them accordingly. The trouble is, when you have what we call "Rank 6" fire behaviour in the form of a continuous crown fire (spreading primarily through the upper canopy of a predominantly coniferous forest), with flame lengths several metres high, fire suppression is nearly impossible during the peak burning period. In short, if it seems like not much progress is being made this afternoon, it's because there isn't. Any water or fire retardant must be dropped aerially on the perimeter of the fire to stop its spread since it is too volatile for ground crews to work close to the fire during peak burning conditions. However, with such intense heat, most or all of the water vapourizes before it even reaches the flames. It is truly a desperate feeling knowing you cannot stop such a natural process.

Fire suppression is more effective at night and in the early morning, when temperatures normally cool, winds die down, and RH increases. During the night, while ground crews may be able to get in, all VFR aerial support is grounded. If winds continue to blow through the night, this recovery period may not occur. Tomorrow is forecasted to be roughly a carbon copy of today being hot and windy, with less recovery overnight tonight than we'd hope. Thus, we can expect the extreme fire behaviour to continue, unfortunately. Fire whirls, pyrocumulus clouds in excess of 20000 feet, large flame lengths, and spot fires are all signs of extreme fire behaviour and we have been seeing all of these today. Compared to Slave Lake in 2011, surface winds of 70-90km/h contributed to the rapid rates of spread then. However this year it is hotter and drier overall, and still with moderate winds.

Prayers for Fort Mac.

(Attached map is the forecasted Fire Danger for tomorrow (May 4). Areas in purple indicate extreme fire danger.)