US, Canada: Flooding possible across northwestern US and southwestern Canada due to heavy rainfall and snow melt through at least June 13

Event

A combination of heavy rainfall and melting snow is forecast to bring an increased risk of flooding across northwestern parts of the US and southwestern Canada through at least June 13.

A late-season atmospheric river is forecast to bring persistent rainfall to the Pacific Northwest US June 10, with widespread rainfall totals of 2.5-7.5 cm (1-3 inches) expected across much of Washington and Oregon, as well as into northern Idaho and western Montana. Widespread precipitation will continue across much of the region June 11, with the heaviest rainfall expected in western and northeastern Oregon, eastern Washington, northern Idaho, and northwestern Montana. In addition to the persistent rainfall, rivers will also be fed by melting snow, causing them to rise to dangerous levels and triggering flooding in some low-lying areas.

Many areas of British Columbia have already received more rainfall as of June 9 than the average amount for the whole of June. Further rainfall is forecast in the coming days, with totals of 2-3 cm (0.8-1.1 inches) expected across the South Coast June 10 and lesser amounts over eastern Vancouver Island and the Lower Mainland. The combination of saturated ground from previous downpours, rainfall runoff, and increasing snowmelt will cause rivers to rise to dangerous levels across many parts of the province and will likely trigger flooding in some areas.

Government Advisories
As of early June 10, the US National Weather Service (NWS) has issued a flood warning for the Stehekin River in Washington through June 13. Flood watches have been issued for parts of northern and central Washington, northern Idaho, and western Montana. Hydrologic Outlook statements have been issued across much of Washington, Oregon, northern and central Idaho, and western Montana. NWS's Weather Prediction Center has warned of a "Marginal Risk" (the lowest level on a four-tier scale) of excessive rainfall across parts of western Washington and Oregon June 10-11 and parts of far eastern Washington, far northeastern Oregon, northern Idaho, and western Montana June 10-12.

As of early June 10, the British Columbia River Forecasting Centre has issued flood warnings and watches across the following catchments:

• Flood Warning: Liard River.

• Flood Watch: Bulkley, Dean, and Skeena rivers, as well as the Cariboo Mountains.

• High Streamflow Advisory: North Thompson, Stikine, and Swift Rivers.

Officials could update and possibly extend the coverage of weather alerts over the coming days.

Hazardous Conditions
Sustained heavy rainfall and snow melt could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where the soil has become saturated by heavy rainfall.

Authorities could issue mandatory evacuation orders for flood-prone communities over the coming days. Disruptions to electricity and telecommunications services are possible where significant flooding or landslides impact utility networks.

Transport
Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. Flooding could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation. Severe weather could also trigger flight delays and cancellations at airports across the affected region.

Localized business disruptions may occur in low-lying areas; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.

Advice

Monitor local media for updated emergency and weather information. Seek updated information on weather and road conditions before driving or routing shipments through areas where severe weather is forecast. Plan accordingly for potential delivery delays if routing shipments by truck through the affected area. Stay away from elevated streams, creeks, and other watercourses that are prone to flash flooding. Do not attempt to navigate flooded roadways. Exercise caution in elevated terrain due to the threat of landslides, as well as mountainous regions where avalanches pose a threat. Keep important documents and necessary medications in waterproof containers. Review contingency plans and be prepared to move quickly to shelters if evacuation orders are issued. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

National Weather Service
British Columbia River Forecasting Centre