U.S. National Weather Service substantially lowers American flood forecast for Red River at border
Manitoba Infrastructure and Transportation’s Hydrologic Forecast Centre advises that, due to temperatures well-above freezing this weekend, it is expected that the snowpack will melt quickly throughout most of southern Manitoba. Small tributaries and drains are expected to experience rapid increases in water levels, which could cause ice jams and overtop road crossings. With new information from the U.S. National Weather Service (NWS), the flood outlook on the Red River is now trending toward a favourable weather scenario with lower flows on the Red River from Emerson to Winnipeg. The new information suggests flooding will be similar to what was seen in 2006. The NWS is planning another update this afternoon.
Runoff and Ice Jamming
A rapid snowpack melt this weekend due to warm temperatures and still-frozen soil throughout most of the province will limit the ability of the ground to absorb run-off. The meltwater is expected to run off in a short period of time. Small tributaries and drains are expected to experience rapid increases in water levels – more than typical years – that could cause ice jams and overtop road crossings. Major rivers such as the Red, Qu’Appelle and upper Assiniboine have areas of open water, but there are reaches in which strong ice is still in place.
The possibility of run-off water overtopping roads is significant. The province has steamers that work on provincial roadway culverts to prevent drains from freezing and causing overland flooding. Many municipalities have also been using their own steamers to opens ditches and drains. The provincial fleet of Amphibex ice-breaking machines is on standby to be deployed to serious river ice jams that may result in threatened properties.
Red River Outlook
The U.S. NWS has indicated its forecast is trending toward a lower decile flow rate at Pembina, N.D., of approximately 65,000 cubic feet per second based on current favourable weather conditions and the significant dissipation of snowpack in the Red River Basin. The forecast crest for the Red River at Pembina for the favourable weather scenario could be as early as the second week of May.
The median and upper decile forecasts are still valid in the event of significant precipitation in the next week. However, the long-range weather forecast does not call for significant precipitation events.
The Red River crest is expected to arrive in Winnipeg in the third week of May.
Localized flooding is still expected to occur in small tributaries such as the LaSalle, Roseau, Rat and Morris rivers.
Levels north of Winnipeg are likely to be well below 2011 levels.
With the revised outlook, there is adequate community protection for the Red River Valley ring dike communities and it is unlikely any of these communities will require evacuation due to loss of access.
The 2006 flood caused PTH 75 to be closed 18 days. In 2009, it was closed 36 days and in 2011, 28 days.
It should be noted that further significant precipitation would push the outlook back to the unfavourable weather conditions.
The magnitude of the spring flood is still dependent on future weather conditions from now until the crest occurs in Manitoba. With the above-normal warming trend and little additional precipitation, it is possible that Manitoba tributaries will not crest at the same time. If the local run-off and upstream crest arrive at different times, the trend would be towards the favourable weather scenario.
With the operation of the Red River Floodway, Portage Diversion and Shellmouth Dam the levels at James Avenue in Winnipeg are forecasted to be down slightly to 17.8 feet under favourable weather conditions, 18.75 ft. under average weather conditions and 20.39 ft. under unfavourable weather conditions.
A snow survey was conducted on April 22 and 23 in the Souris, Qu’Appelle and upper Assiniboine basins. It was determined that the snowpack has decreased by 10 per cent since the last snow survey on April 7. The projections for the remainder of Manitoba watersheds such as the Souris, Qu’Appelle, Assiniboine, Saskatchewan and Fisher rivers remains unchanged from the April 10 flood outlook. Lake level projections also remain unchanged.
Spring Safety
People are reminded to stay off ice and water, and not to attempt to drive or walk through fast moving water.
As the spring melt begins, ice conditions are unsafe and turbulent flow maybe encountered.
Stay away from heavy equipment used in flood fighting.
Before travelling, check road conditions by calling 511.
Those who live in flood-prone areas should keep a two-week supply of prescription medication for themselves and their families.
The Manitoba Flood Forecasting Centre will post daily flood forecasts and flood sheets on the provincial website. The flood liaison offices in Winnipeg, Brandon, Arborg and Morris will be open commencing tomorrow.
