The Nahanni River at the top of Virginia Falls. Vadim Nikolaevitch Gouida/Dreamstime
Up to two months of rain could fall in days over the southern Mackenzie Mountains, a situation that has triggered a yellow alert and a warning of possible Dehcho flooding.
In a special bulletin issued on Wednesday, the NWT government said it had “high confidence there will be two 24-hour periods with at least 50 mm of rainfall” between June 29 and July 3, with the heaviest rain expected on June 30 and July 1.
It’s possible, the territory said, that more than 15 cm of rain could fall in a single 24-hour period during that window – but it’s not yet clear where the heaviest rain will land.
“Forecasts suggest Wrigley and the South Nahanni River basin could see very significant rainfall,” the territory’s Department of Environment and Climate Change stated in its bulletin.
“When compared to historic data for the general area, this means that one to two months worth of rain for this time of year could potentially fall within a matter of days.”
All of that rain, if it does fall, could mean “rapid rises in water levels and flow along these rivers,” the department stated, noting that Environment and Climate Change Canada had already issued a yellow weather alert for the region.
The territorial government said the community of Nahanni Butte, in particular, should be on alert.
Residents of Nahanni Butte “should be aware of this system, monitor conditions closely, and assess any risks to their community based on those conditions,” the territory stated.
“Those planning to be out on the land over the long weekend should be aware that this storm system may cause rapid rises in water levels and flow. Be prepared with communication methods before you go out on the land, know the conditions, and be prepared to leave your cabin or camp on short notice should flooding become imminent.”
Residents are urged to update their household’s emergency plan and have an emergency kit ready to go.
Nahanni Butte last suffered a significant flood in 2012 but endured a near-miss last year, when floodwater receded at a point fractionally below the marker that would trigger an evacuation.