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'Atmospheric river' forecast to blast Pacific Northwest with heavy rain and feet of snow
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useapen
Dec 2, 2023, 2:02:59 AM12/2/23
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Several storms will blast the Northwest over the next few days, courtesy
of multiple atmospheric rivers that are forecast to dump heavy rain and
feet of snow across the region.
"A series of storms will come ashore in the Northwest late this week,"
said AccuWeather senior meteorologist Heather Zehr. "Additional storms
will carry on even into next week."
Coastal and lower elevations of Washington and Oregon will see moderate to
locally heavy rain, the National Weather Service said, with the heavier
rainfall more likely Friday and then into the weekend.
The weather service in Seattle said "multiple atmospheric rivers look to
impact our region this weekend and into next week with possible heavy rain
and breezy conditions."
"Heavy snow likely adding up to at least a few feet is expected across the
Cascades, including many mountain passes. Travel will be difficult to
hazardous due to both heavy snow and blowing snow," the weather service
said.
What is an atmospheric river?
AccuWeather defines an atmospheric river as a "phenomenon where a flow of
moisture from the Pacific Ocean resembles a fire hose that delivers near-
constant rain and higher-elevation snow to the western United States or
British Columbia."
Made visible by clouds, these ribbons of water vapor extend thousands of
miles from the tropics to the western U.S. At 250 to 375 miles wide, they
provide the fuel for massive rain and snowstorms that can cause flooding
along the West Coast.
In general, atmospheric rivers pick up water vapor from the warm, moist
air of tropical regions and then drop the water over land in cooler
regions as rain or snow.
These "rivers in the sky" are responsible for up to 65% of the western
USA's extreme rain and snow events, a 2017 study said. And on average, up
to 50% of the annual precipitation on the West Coast occurs in just a few
atmospheric river events.
Speaking about this week's incoming storms, AccuWeather senior
meteorologist Mike Doll said "this particular atmospheric river setup
extends for more than 7,000 miles from all the way across the Pacific
Ocean to the northern part of the Indian Ocean basin."
'Rivers in the sky':What exactly is an atmospheric river?
Feet of snow possible
"These storms will be accompanied by cold air at first," Zehr said.
"Through the weekend, snow levels will be down below 2,000 feet at times,
leading to accumulations of 2-3 feet and major travel impacts in the
Cascade passes."
Moisture will also spread inland through the Great Basin and Northern
Rockies, with a rain/snow mix for lower elevations and moderate to heavy
snow in the regional mountain ranges, the weather service said.
"Heavy snow is likely to reach into several mountain ranges from Idaho and
Montana to Colorado," the weather service said. "The highest peaks are
forecast see as much as 1 to 3 feet of snow."
Heavy rain could lead to flooding
"Total rainfall amounts through Wednesday from these systems of several
inches over the lowlands to upwards of 10 inches or more in the Cascades
and Olympics will lead to rapid rises on rivers, especially combined with
melting as snow levels rise Sunday into the first half of next week," the
weather service in Seattle said.
Several inches of rain will fall on both the Seattle and Portland metro
areas throughout the next few days. A flood watch was in effect for both
metro areas.
"River flooding will be possible on more susceptible rivers such as the
Skokomish River in Mason County, but may also include other rivers in the
Olympic and Cascade basins," the weather service said.
Not all bad news: Storms could ease drought
"The incoming moisture, while carrying several threats, is not all bad
news – it will help to relieve drought conditions in the region," said
Bill Deger, AccuWeather senior meteorologist. According to the latest U.S.
Drought Monitor, much of western Washington and western Oregon are
enduring moderate to severe drought conditions.
https://www.usatoday.com/story/news/weather/2023/11/30/atmospheric-river-
to-blast-northwest-with-heavy-rain-and-feet-of-snow/71755001007/
https://www.scientificamerican.com/article/megastorms-could-down-massive-
portions-of-california/
https://www.atmosedu.com/Geol390/articles/ComingMegaFloos4.pdf
of multiple atmospheric rivers that are forecast to dump heavy rain and
feet of snow across the region.
"A series of storms will come ashore in the Northwest late this week,"
said AccuWeather senior meteorologist Heather Zehr. "Additional storms
will carry on even into next week."
Coastal and lower elevations of Washington and Oregon will see moderate to
locally heavy rain, the National Weather Service said, with the heavier
rainfall more likely Friday and then into the weekend.
The weather service in Seattle said "multiple atmospheric rivers look to
impact our region this weekend and into next week with possible heavy rain
and breezy conditions."
"Heavy snow likely adding up to at least a few feet is expected across the
Cascades, including many mountain passes. Travel will be difficult to
hazardous due to both heavy snow and blowing snow," the weather service
said.
What is an atmospheric river?
AccuWeather defines an atmospheric river as a "phenomenon where a flow of
moisture from the Pacific Ocean resembles a fire hose that delivers near-
constant rain and higher-elevation snow to the western United States or
British Columbia."
Made visible by clouds, these ribbons of water vapor extend thousands of
miles from the tropics to the western U.S. At 250 to 375 miles wide, they
provide the fuel for massive rain and snowstorms that can cause flooding
along the West Coast.
In general, atmospheric rivers pick up water vapor from the warm, moist
air of tropical regions and then drop the water over land in cooler
regions as rain or snow.
These "rivers in the sky" are responsible for up to 65% of the western
USA's extreme rain and snow events, a 2017 study said. And on average, up
to 50% of the annual precipitation on the West Coast occurs in just a few
atmospheric river events.
Speaking about this week's incoming storms, AccuWeather senior
meteorologist Mike Doll said "this particular atmospheric river setup
extends for more than 7,000 miles from all the way across the Pacific
Ocean to the northern part of the Indian Ocean basin."
'Rivers in the sky':What exactly is an atmospheric river?
Feet of snow possible
"These storms will be accompanied by cold air at first," Zehr said.
"Through the weekend, snow levels will be down below 2,000 feet at times,
leading to accumulations of 2-3 feet and major travel impacts in the
Cascade passes."
Moisture will also spread inland through the Great Basin and Northern
Rockies, with a rain/snow mix for lower elevations and moderate to heavy
snow in the regional mountain ranges, the weather service said.
"Heavy snow is likely to reach into several mountain ranges from Idaho and
Montana to Colorado," the weather service said. "The highest peaks are
forecast see as much as 1 to 3 feet of snow."
Heavy rain could lead to flooding
"Total rainfall amounts through Wednesday from these systems of several
inches over the lowlands to upwards of 10 inches or more in the Cascades
and Olympics will lead to rapid rises on rivers, especially combined with
melting as snow levels rise Sunday into the first half of next week," the
weather service in Seattle said.
Several inches of rain will fall on both the Seattle and Portland metro
areas throughout the next few days. A flood watch was in effect for both
metro areas.
"River flooding will be possible on more susceptible rivers such as the
Skokomish River in Mason County, but may also include other rivers in the
Olympic and Cascade basins," the weather service said.
Not all bad news: Storms could ease drought
"The incoming moisture, while carrying several threats, is not all bad
news – it will help to relieve drought conditions in the region," said
Bill Deger, AccuWeather senior meteorologist. According to the latest U.S.
Drought Monitor, much of western Washington and western Oregon are
enduring moderate to severe drought conditions.
https://www.usatoday.com/story/news/weather/2023/11/30/atmospheric-river-
to-blast-northwest-with-heavy-rain-and-feet-of-snow/71755001007/
https://www.scientificamerican.com/article/megastorms-could-down-massive-
portions-of-california/
https://www.atmosedu.com/Geol390/articles/ComingMegaFloos4.pdf
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