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Western US weather

Powerful storm to slam West at end of week

By Jordan Root, AccuWeather meteorologist

A round of heavy rain, mountain snow and gusty winds will impact the Western U.S. at the end of the week, most notably Oregon and California, which will face the worst impacts.

west storm 4/5 overview

Let's take a look at some of the players on the field for this storm. The first is a very strong jet stream across the Pacific Ocean. The image below shows winds about 35,000 feet aloft in the atmosphere. Notice the colors across the Central Pacific. Winds were initialized near 200 mph this morning for the GFS model run. Impressive!

250 mb ca 4/5

A very strong jet stream is currently ripping across the central Pacific as shown in the above image. These winds will help drive a very strong low pressure system near the West Coast late Thursday through Saturday. Model shown is 12 Wed. GFS.

This jet will weaken a bit heading into the end of the week but it will still be strong and will help rapidly strengthen a surface low that will track near the northwestern California Coast and northward along the Northwest U.S. coastline.

This strong low pressure system will develop a strong southwesterly flow that will pull a stream of anomalously high moisture from the tropics, which is known as an atmospheric river.

pwat ca 4/5

An atmospheric river will accompany the storm system at the end of the week, leading to heavy rain and flooding. Model shown is 12 Wed. GFS precipitable water and 850 mb wind.

The combination of these strong winds and surge of moisture will lead to a rather potent storm system for Oregon and northern and central California late Thursday through Saturday.

Very strong winds are expected with gusts up to 70 mph along the north-central California coast to the Washington coast. These winds will be able to cause damage. Wind gusts of 50 to 60 mph are likely elsewhere across Oregon, Nevada, and northern California.

llj ca 4/5

A strong low-level jet is shown in the image above. This low-level jet will bring strong winds to Washington, Oregon and California late Thursday and Friday. The strongest winds of up to 70 mph will be at the coast but strong winds will also be inland as well. Model shown is 12 Wed. GFS.

Rainfall amounts of 3 to 6 inches are expected across the Coastal Range and foothills of the Cascades and Sierra Nevada. This, plus additional water from melting snow in the mountains, will lead to quick stream and river rises and possible flooding in some locations.

While snow levels initially will be high, they will fall through Saturday. The heaviest snow will occur across the Sierra where a few feet will fall by Saturday.

There will be a reinforcing storm system that will swing into northern California late Friday which will produce another round of heavier precipitation. There will also be the threat for thunderstorms and even some small hail.

end of week ca 4/5 storms

There will actually be two pieces of energy that impact the West at the end of the week and into the weekend. The first one will be the most vigorous and will swing through Thursday and Friday. Another piece of energy will bring another round of heavy precipitation late Friday and Saturday. Image shown is 12 Wed. GFS 500 mb and vorticity.

Outside of a few showers Friday night into Saturday, Southern California will miss out on most of the unsettled weather.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Western US weather