The first river breakup forecast issued by the Yukon government for this spring suggest an increased likelihood of ice jamming and high water levels in some areas as the ice surface on rivers breaks up and flows down stream.
The April 26 bulletin dealing with the area around Dawson City states that water levels began to rise around April 21 but the forecast for the rest of the spring is uncertain due to cool April weather and a delayed thaw. At Dawson, the conditions of the Klondike River suggest high potential for flooding if water flow increases rapidly. A moderate probability of a sudden rise in water levels starting next week is also forecast for the Yukon River.
The cool temperatures and overcast days have delayed visible signs of the ice melting or beginning to break up.
A slow rise in the water levels in the river is being observed but the forecast bulletin suggests the potential for a significant rise in the freezing elevation upstream of Dawson City. This could lead to a rapid increase in the amount of water discharging into the rivers in the area.
There is plenty of snow to melt and discharge with the snow water equivalent level being observed near Dawson at 132 per cent of the historical median according to the most recent snow bulletin released April 1. Record precipitation for the Dawson airport weather station was recorded last October and a notable amount of snow also fell in January. This is an appreciably different situation from the southern Yukon where snow pack ranges from 106 per cent of the historical average to 114 per cent.
The survey states that the April 1 snow survey usually represents peak of the snow pack in the territory and the melt usually begins showing less overall snow on the mountains by early May.
“It is too early to judge how resistant the ice cover is but the lack of visible degradation at this time suggests a dynamic breakup is likely with a potential for ice jam flooding. A sudden sustained rise of air temperatures above 15 C is likely to result in a more severe breakup,” the breakup forecast reads.
The government notice states that the situation is being closely monitored but they appreciate any relevant information or observations.
Although the snow pack set to melt this spring pales in comparison to last year’s record or near-record levels observed across much of the territory, the April 1 snow survey suggests that the high groundwater tables left behind combined with this winter’s snowpack will have an impact on runoff territory-wide. The snow survey suggests runoff flowing through creeks and streams draining into the Yukon River and its tributaries will be slightly above average.
Assuming the weather remains normal through the freshet, the Southern Lakes are expected to only reach a slightly above average high-water mark.
-With files from Dana Hatherly
Contact Jim Elliot at email@example.com