Torrential downpours unleashed by an “intense plume” of volatility in the wake of “one of the biggest storms of winter” threatens flooding and even avalanches.
A barrage of storms culminated this weekend in a mega-assault aiming a ‘firehose’ of rain at the Pacific coast.
North-western states through this week will remain at the mercy of a moisture-laden ‘atmospheric river’ ready to burst in a cascade of rainfall.
A huge weekend storm dumping inches of rain with milder winds and snowmelt has now triggered an avalanche risk.
AccuWeather map shows storm patterns and areas at risk of mudslides and avalanchesAccuWeatherAccuWeather senior meteorologist Alex Sosnowski said: “As the thaw reaches into the mountains, the risk of avalanches, mudslides and other debris flows and slides will increase in the hilly terrain, including the well-travelled passes that remain open in the winter months.
“The storm from Monday to Tuesday could pack a punch in terms of drenching rain at the lower elevations, but mainly from north-western Washington to southwestern British Columbia.
“As a series of Pacific storms continues in the north-western United States and in southwestern Canada, the biggest storm of the bunch will include an atmospheric river in portions of Washington and Oregon that can have dangerous and damaging consequences.”
Swaths of the US have been hit by storms through the past week as a savage Arctic freeze triggered record-low temperatures.
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Major storm eyes up the west
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While temperatures are forecast to rise this week, relentless rainfall and snowmelt will bring a new risk of flooding.
Atmospheric rivers – bands of intense rainfall sweeping in from the northwest – often join forces with trains of storms heading in from the Pacific.
This chaotic union will dominate the US weather through the week with strong winds threatening to topple trees and power lines.
Sosnowski said: “The storms will bring bouts of gusty winds to the coast, and winds could be strong enough to knock over some trees and trigger sporadic power outages.
“An atmospheric river will be unleashed as a fire hose of rain even well up into the higher elevations of the Olympics and west-facing slopes of the Cascades.
“As the biggest storm in the bunch pushes inland, additional rounds of moisture from somewhat weaker storms will be accompanied by lowering snow levels.”
AccuWeather map shows peak wind gusts
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The US National Weather Service (NOAA) has storm and high-surf warnings in force along the Pacific coast.
Further advisories inland warn of an ongoing risk of floods, high winds and avalanches.
A NOAA spokesman said: “An active Pacific storm track/Atmospheric River will continue to bring very heavy rain, scattered instances of flooding, and gusty winds from the Pacific Northwest and far northern California.
“Locally heavy downpours are expected, particularly for areas of South Florida Monday where some isolated instances of flooding in urban areas will be possible.
“Heavy rainfall and runoff from snowmelt will lead to some isolated instances of flooding with some very strong winds and gusts up to 60mph.”
Heavy rain, snow and snow melt will risk mudslides where ground is saturated and higher in the mountains, avalanches.
Ethan Greene, director of the Colorado Avalanche Information Centre, said: “This time of year is the most dangerous in terms of the number of people that get killed each month over a long period of time.”
