(CNN) – An “atmospheric river” known as the “Pineapple Express” is expected to carry an extended period of wet weather and the possibility of avalanches to Washington and Oregon from Sunday.
The effects of heavy rain and snow from the mountains will be felt earlier this week. Since the ground has already been saturated from previous storms, flooding is possible even with the few inches of rain the storm is expected to produce.
For much of Washington’s Cascades, avalanche warnings have been issued in advance of this heavy snowfall. The Northwest Avalanche Center has issued a “high” avalanche danger warning (level 4 of 5) for Sunday. Large natural avalanches are possible even at lower altitudes.
According to the Colorado Avalanche Information Center, 30 people have been killed by avalanches in the United States this winter season.
“This will usher in a wet spell in western Washington, as the atmospheric river’s southern periphery will affect the region before it moves south across the area Monday,” the Weather Service office warned Saturday. National in Seattle.
This could be another notable weather event for parts of Washington and Oregon, with localized flooding in cities and rivers along with gusts of wind that could lead to power outages in both states.
Seattle has an average of three inches of rain in February, but the city has already had more than three inches of rain this year, a surplus of three inches.
This new system is because Oregon still has 30,000 customers without power due to a storm last week.
From Sunday to early Tuesday, heavier rain falls with increasing snow levels and gusty winds. Stay tuned for the weather forecast in the coming days! #wawx pic.twitter.com/9Gk9IOEmmP
– NWS Seattle (@NWSSeattle) February 19, 2021
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How a Pineapple Express is formed
Atmospheric rivers are narrow corridors in the upper atmosphere that carry intense moisture from a large amount of water to land, like rivers in the air. This particular atmospheric river event is special in terms of where the moisture comes from: Hawaii.
Originally from near Hawaii, the Pineapple Express travels across the Pacific Ocean to the west coast of North America.
When you connect that narrow transport corridor to the tropical humidity of the Pacific Ocean around Hawaii, it can flood the west coast with heavy rain and snow.
Not all atmospheric rivers are disturbing. However, those that collect large amounts of water vapor and high winds can cause extreme rainfall and subsequent flooding.
“If it hits the West Coast, the Pineapple Express can dump up to four inches of rain in California in one day,” said the National Oceanic and Atmospheric Administration.
An atmospheric river event in January threw 12 to 25 inches of rain over the Olympic Peninsula and far northwestern Oregon. Heavy rains caused widespread flooding and landslides, while strong winds caused significant tree damage and power outages in western Washington and northwest Oregon.
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Everything is expected to rise
Strong winds, high tides and a high potential for river flooding will be factors in the next storm.
The wind will vary constantly from 25 to 40 km / h, with gusts of wind up to 65 km in the next 72 hours.
Wind gusts, which are strongest near the coast, can cause power outages. This is a major concern as there are still thousands of people without power in Oregon due to the winter storm that hit more than a week ago. This next storm could delay power recovery for several more days.
The heaviest rain will stretch from Eugene, Oregon, to the Canadian border. Widespread rainfall of 5-10 centimeters is expected for the low-lying coastal areas and 7-15 centimeters for the Olympics and Cascades.
Floods will be a concern not only because of the amount of rain expected to fall, but also because the ground is already nearly saturated in many places and there will also be some melting snow.
Snowfall will be limited to the higher elevations, but will be heavy. Totals generally range from 12 ” to 12 ” at White and Stevens Pass, and from 8 ” to 12 ” at Snoqualmie Pass.
Small boat advisories are in effect on Sundays, indicating that tides of 10 feet or more are expected to create dangerous wave conditions.
More storm systems are likely to occur by the end of next week, so keep waterproof jackets and umbrellas handy.