Spring drought fuels dangerous wildfire season on Prairies
Meteorologist
Tuesday, May 1, 2018, 1:39 PM - Flood, fire, and drought. The Prairies are experiencing a wide array of different weather conditions. In one corner of the Prairies, local states of emergency and flood evacuations are plaguing northern Alberta. A persistent ridge of high pressure has accelerated snowmelt at a hectic pace – the consequences have been significant as overland flooding pools across the province. But, a more subtle story is expanding across the Prairies. The threat from fire and drought.
DROUGHT HIGHLIGHTS
- Pockets of extreme drought conditions spreading across Saskatchewan and Manitoba
- Early start to grass fire season
- No relief in sight for the region plagued by drought
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Wildfires and grass fires flourish in droughts, and unlike flooding, the subtle nuances with respect to drought are a little more masked and require careful observation. April has seen a significant precipitation abnormality develop, specifically across southern Saskatchewan and Manitoba.
How bad has it been? Winnipeg, let's use you as an example. A formidable dry streak has blossomed:
After all is said and done, for the month of April, Winnipeg will have strung together 18 straight days being precipitation free. But, what's a normal precipitation amount for Winnipeg in April?
For the entire month of April, 1.7 mm of precipitation was recorded, making this April the 4th driest on record:
Using 1980-2010 climate normal data, 30 mm of precipitation is expected for the month. In other words, Winnipeg received less than 6% of normal precipitation values. In rare cases, Winnipeg can pick up this precipitation amount in a single day during the month of April, which was the case on April 30th, 1986 where 36 mm fell on Richardson International Airport.
Although drought has significant ramifications for the growing season, there's another dangerous byproduct. Fires have been popping up across much of southern Saskatchewan and Manitoba – a direct consequence of warm temperatures, dry relative humidity levels, and gusty winds.
Why are portions of the Prairies dealing with such serious wildfire conditions, especially in April, a month not known for a severe fire season in the Prairies?
Fire conditions are multi-faceted and complex, but I want to look a few key features: moisture, wind, and temperature.
The drought has set the stage, with below normal soil moisture; consequently, the daily weather patterns have created high fire danger, particularly in the afternoon hours. Why is that time period so risky? Here's an important term...
CROSS OVER POINT: The point where the temperature (°C) crosses the relative humidity (%) – a benchmark known to create severe fire conditions. It's a value firefighters are trained to be aware of, and it normally follows a diurnal cycle and peaks in the afternoon. On April 29th, Estevan, SK recorded a maximum temperature of nearly 26°C, while the relative humidity fell to 27%, dangerously close to this dangerous benchmark – pretty amazing, but also disconcerting for April.
These conditions create the most volatile fire weather conditions and often, aggressive fire behaviour occurs during these conditions.
WIND: To create dangerous fire conditions, another parameter is necessary that relates to the rate of fire spread. Wind. And, it just happens that Winnipeg recorded significant winds on April 29th, with sustained winds of 60 km/h, the windiest conditions in over seven weeks. These parameters paired together are near-perfect for breeding dangerous grass fires, and the public must be on alert and be extra vigilant, as fires can quickly grow out of control in a matter of minutes.
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CURRENT DROUGHT CONDITIONS (courtesy: Agriculture Canada)
The latest April analysis is due out shortly, but it wouldn't be surprising to see the extreme drought expand spatially across a larger area, considering the long stretches of dry weather observed during April. In the short-term, we're anticipating another high to extreme fire danger on Thursday. Extreme fires can be particularly challenging to contain due to their aggressive fire behaviour and fast rate of spread.
How rare is the extreme drought category? The red locations near Weyburn, SK highlight an event that occurs about every 20 years or so.
FUTURE PRECIPITATION FORECAST
As you can see, significant precipitation is not expected over the next seven days, and warmer temperatures are set to impact the region in waves, stemming from strong high pressure situated over British Columbia. In fact, this pattern looks similar to what has been experienced over western Canada to finish off April.
