An unusually powerful force is fueling weather hazards in the northwestern United States and Canada, including an intense atmospheric river headed to California.
The record-strong low-pressure system is developing offshore of Oregon and Washington, causing low air pressure that is more typical of a major hurricane.
Why is this atmospheric river unusual?
Story continues below advertisement But what’s most unusual about this atmospheric river is the intense low that’s driving it.
The animation below shows the atmospheric river as it flows into the region from Tuesday night through Friday.
Weather hazards in the northwest of the United States and Canada, including a strong atmospheric river that is en route to California, are being fueled by an exceptionally strong force. Off the coasts of Oregon and Washington, a record-strong low-pressure system is forming, resulting in low air pressure more suited for a powerful hurricane.
A buoy near the storm’s center off the coast of Washington reported 950 millibars of air pressure and 74-mph wind gusts on Tuesday night. Winds were predicted to get stronger along the Oregon and Washington coastlines through Tuesday evening, even though the storm’s center would stay offshore.
An atmospheric river of moisture is one of several threats that will persist into the weekend. It will stretch 2,000 miles across the Pacific, from Hawaii to Northern California, where it will touch down on Tuesday evening. It is predicted to bring extremely heavy snow to the Klamath Mountains and 10 to 20 inches of rain to California’s northern Coast Ranges.
British Columbia, Washington, and Oregon will be hit by strong, potentially destructive winds, mountain snow, and heavy rain. Additionally, snow will fall in Saskatchewan, Montana, Alberta, and Idaho.
What is unusual about this atmospheric river?
The long, comparatively narrow, concentrated plumes of water vapor known as atmospheric rivers carry moisture and heat from the tropics to the poles.
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The length of time and degree of moisture transport are used to rank these rivers in the sky. The one that is predicted to reach land in Northern California on Tuesday night is a strong atmospheric river with a Category 4 (out of 5) rating, which is noteworthy for its extended duration.
The extreme low that is propelling this atmospheric river, however, is what makes it most unique.
It is predicted that a low-pressure system off the Northwest coast will intensify so quickly on Tuesday that it will be considered a meteorological bomb. Though the required rate of intensification varies by latitude, this occurs when a storm’s central pressure drops by more than 24 millibars in a 24-hour period.
With a predicted depth of 984 millibars Tuesday morning and 943 millibars in the evening, this storm is expected to easily become a bomb cyclone in half the time needed to qualify.
The purple shading off the coast of Washington state in the image below indicates the storm’s location during what should be its strongest moment on Tuesday night.
historic low pressure, more akin to a powerful hurricane.
According to a study of atmospheric pressure going back to the 1940s, this storm should be the strongest November storm in the area by roughly 15 millibars. The storm is as strong as a Category 4 hurricane based on its minimum central air pressure, which illustrates the fierceness of its anticipated effects.
The storm is expected to break November air pressure records in the blue-shaded areas in the image below.
Why is this intensity occurring?
As a very loopy jet stream is forced to move around a powerful ridge of high pressure centered over the Bering Sea before making a significant dip southward off the Northwest coast, the storm will intensify.
Unusual jet stream patterns this fall have been influenced by a North Pacific marine heat wave, which is the backdrop against which this pattern is occurring. As the world warms, marine heat waves are predicted to occur more frequently.
It is anticipated that a secondary low-pressure system strengthening offshore from late Thursday into Friday will intensify the slow-moving storm, bringing with it more torrential rain and heavy mountain snow.
Over 2,500 feet in elevation, the Cascade Mountains of Washington are under a blizzard warning, meaning that there could be more than a foot of snowfall overall and 60 mph wind gusts. Similar forecasts for British Columbia indicate that there will be a lot of snowfall in areas east of Vancouver and across the Vancouver Island Ranges.
The atmospheric river is depicted in the animation below as it enters the area Tuesday evening through Friday.
Over the weekend, the region should see less intense rain and snow before a drier pattern takes over the following week.
However, a La Niña-like pattern and an active northern branch of the jet stream could support an active winter season throughout the Northwest, and this could just be the beginning.
