NWT issues first major outlook for 2025 flood and breakup season

The NWT’s season-opening spring breakup forecast suggests most parts of the territory have a reduced – but not entirely eliminated – risk of flooding in the weeks and months ahead.

Water levels and flows are lower than usual on many of the NWT’s rivers.

A territorial government outlook published on Wednesday projected lower-than-normal spring flows on the Hay River, Liard River and Mackenzie River.

While there are lots of factors that can cause a flood, low river flow – the total amount of water moving through the river in the spring – helps to reduce flooding risk.

As a result, this week’s forecast can be interpreted as positive news for communities like Hay River, Fort Liard, Jean Marie River, Fort Simpson, Tulita and Fort Good Hope.

Even so, the GNWT cautioned: “There is always a possibility that anomalous spring weather conditions can cause high water levels and out-of-bank flows.”

Ice jams on rivers can trigger floods even when water levels and flows are low, and those jams remain difficult to predict.

The GNWT’s outlook stated the potential for flooding in Nahanni Butte is “average” in the months ahead and rests heavily on how much rainfall arrives in June, as well as how quickly snow at higher altitudes melts.

While water levels on the South Nahanni River are well above average, those on the Liard River are below average and the snowpack is below average.

Fort McPherson is the other NWT community facing “average” conditions heading into spring breakup.

Water levels on the Peel River, snowpack and flows are all described as average in the outlook. “The likelihood of out-of-bank flows will depend on spring weather conditions, including how quickly the snow melts and how river ice degrades,” the report states.

“As the spring melt season begins, water levels across the territory are generally lower than average with some exceptions,” a summary of the report stated.

“The summer and fall of 2024 were warmer and drier than normal across most of the NWT. These warm and dry conditions have resulted in continued low water levels that have persisted since the late summer of 2022.”

The Peel River, South Nahanni River and some smaller rivers in the Great Slave Lake basin are exceptions to the general low-water rule.

Snowpack across the territory in the winter of 2024-25 was higher than normal in eastern and southeastern portions of the territory, including in the Yellowknife River basin and Taltson River basin.

“Snowpack for all other basins was approximately average to below average,” the summary stated, drawing from snow surveys conducted in late March.

A lot of attention in the weeks ahead will be paid to the prospect of ice jams that could turn an otherwise ordinary spring breakup into a problem.

“The occurrence of ice jams is primarily dependent on weather conditions just prior to and during breakup. These weather conditions will influence how much and how quickly snowmelt water reaches river systems and how the ice breaks up,” the GNWT’s outlook stated.

“The potential severity of flooding, if an ice jam occurs, is higher when water levels are already high, when snowpacks are large, and when river ice is thick.”