What are the ‘atmospheric rivers’ hitting the US West Coast? | Weather News

Large ‘atmospheric rivers’ have resulted in torrential downpours, excessive winds and flood watches.

Channels of moisture known as “atmospheric rivers” are at the moment stretching alongside the US West Coast to central California from the tropical skies north of Hawaii.

The centre of this moisture plume is about 200 to 300 miles (320-480km) vast.

The climate system spawned by a low-pressure system off the Pacific Northwest has resulted in persevering with torrential downpours alongside the coast, with many areas positioned beneath a flood watch.

What’s an ‘atmospheric river’?

An “atmospheric river” is a comparatively lengthy, slender area that transports columns of water vapour away from the tropics within the environment.

In response to the Nationwide Oceanic and Atmospheric Administration (NOAA), these columns can carry roughly 7.5 to fifteen instances the typical move of water on the mouth of the Mississippi River.

When the atmospheric rivers attain land, they usually launch these columns of water vapour within the type of rain or snow.

On common, the West Coast receives between 30 p.c and 50 p.c of its annual precipitation by means of “atmospheric rivers”, in response to the NOAA.

Are ‘atmospheric rivers’ harmful?

“Atmospheric rivers” are a typical phenomenon alongside the US West Coast and are often innocent.

Weaker storms present helpful quantities of rain for the water provide. In addition they assist enhance California’s mountain snowpack, which offers a 3rd of the state’s water provide.

“Atmospheric rivers” are ranked on a scale of 1-5 based mostly on how a lot moisture they transport from the tropics to the mid-latitudes.

Nonetheless, class 4 or 5 “atmospheric rivers” that produce giant portions of rain can lead to extreme flooding, induce mudslides and trigger catastrophic injury to life and property, in response to the NOAA.

The Heart for Western Climate and Water Extremes has ranked the persevering with “atmospheric river” occasion as a Stage 4, which corresponds to “excessive” moisture transport.

How have they affected the West Coast this week?

The “atmospheric rivers” have resulted in torrential downpours within the San Francisco Bay Space since Monday night time, with quite a few reviews of roadway flooding and downed timber and branches.

Some elements of central California have already registered greater than 5 inches (12.7cm) of rain.

Pacific Gasoline & Electrical’s web site confirmed quite a few energy outages scattered throughout Northern California.

A second “atmospheric river” is forecast for later this week and weekend and is predicted to carry additional heavy rainfall and a risk of flooding.

A number of toes of snow are anticipated within the Sierra Nevada mountain vary. Backcountry avalanche warnings had been issued for elements of the mountain vary.

The current rain and snowfall are additionally anticipated to supply some aid to drought-stricken areas and supply some surplus water for doubtlessly drier months.