Fort McMurray to see some rain. Will it be enough?

Friday, May 20, 2016, 11:55 AM - It’s the news everyone has been waiting to hear: Fort McMurray is finally going to get some rain.

FORT MCMURRAY FIRE COVERAGE: Get everything you need to know about the fires, here

While it may not be much compared to other parts of Alberta and Saskatchewan, the region immediately surrounding Fort McMurray is forecast to receive roughly 5 mm of rain a day between today and Victoria Day, totaling roughly 20 mm.

If this verifies, this will be the most precipitation the community will have seen in a one-month period since back in September, 2015.

You read that right.

According to Environment Canada’s Daily data report for the Fort McMurray airport, between October 1st, 2015 and May 18th, 2016, no month has exceeded a precipitation total of more than 17.5 mm, which occurred back in early April of this year. 

Perhaps more distressing, however, is the fact that only 61 mm of precipitation has been recorded at the Fort McMurray airport since October 1st, 2015, with 0 mm so far in the month of May. 

If you think this sounds anomalously low, you’d be absolutely right: 61 mm since October 1st, 2015 of rain is a mere 40% of the roughly 150 mm of precipitation that this region normally sees in this time, according to climate normal data for this location between 1981 and 2010.

Without a doubt, this lack of precipitation has been one of the largest contributing factors to the severity and extensive coverage of this wildfire; the other main factor is the strong, gusty winds that have allowed the fire to balloon to over 500,000 hectares in size.

So where’s the rain coming from?

A series of low-pressure systems will be tracking northward from Montana into Alberta and Saskatchewan over the next few days. The first one is forecast to bring a whopping 75 mm of rain between Thursday and Friday for the area stretching northwest of Edmonton toward the B.C. border, with eastern Alberta seeing significantly less.

The subsequent system into the weekend will be less moisture-laden than the first, but impact a broader region – covering much of both Alberta and Saskatchewan.

Although there is some model disagreement in the projected rainfall accumulation totals, confidence is fairly high that much of Alberta and Saskatchewan will receive at least some rain over the next 72-96h.

This is because of a favourable set-up in the upper levels of the atmosphere – a deep trough situated over B.C. and Alberta – which will keep temperatures cool and favour widespread rain across the western Prairies.

Too little too late?

While it may be tempting to assume that rain in the forecast will lead to immediate relief for the Fort McMurray region, it is looking unlikely that the 5 mm/day will have a significant impact on the wildfire.

This is because it likely that much of the rain that does in fact fall over the areas presently ablaze will evaporate quickly, leading to minimal amounts actually reaching the surface and saturating it.

According to Dr. Kerry Anderson, a research scientist with the Canadian Forest Service in Edmonton, “A fire such as this Fort McMurray fire is going to need 50 mm or 100 mm of rain to put it out … “ (Macleans, May 5th, 2016).

Chad Morrison, a wildfire manager interviewed by CBC on May 8, 2016, puts the required amount of rain even higher: “Unless there's a significant rain event of 100 mm or more, we expect to be fighting the fire for months to come.”

Wind complications

To make matters worse, the associated winds in the region have the potential to worsen the situation before it gets better.

Gusty northeast winds with gusts up over 40 km/h were reported Thursday evening. Under these conditions, as we have seen near the beginning of this wildfire, the size of the wildfire can increase rapidly.

Friday’s wind gusts will be more in the area of 20 km/h, while both Saturday and Sunday should be much calmer with gusts below 20 km/h.

So even though the amount of rain in the forecast may not be enough to quell the fire entirely, it’s certainly better than nothing.