Atmospheric River to Hit the Pacific Northwest from Early This Week: Weather Forecast

An atmospheric river has been forecasted to hit the Pacific Northwest with heavy rain, massive flooding, and snow from early this week.

The US weather forecast shows that the states of Oregon and Washington can be affected by torrential rain and flash floods.

Weather Forecast in the Pacific Northwest

According to CNN, there is a forecast of an atmospheric river, classified as a 'mostly hazardous' category 4 out of 5 in the atmospheric river scale, which can cause significant rainfall, flooding, and snowfall in the Pacific Northwest this week; from Sunday evening to Tuesday morning, Feb. 27 to Mar. 1.

Based on the forecast, the accumulation of three to six inches of rainfall is possible for a total of 24 hours in the coastal areas of Oregon and Washington.

The occurrence of widespread flooding from overflowing rivers and high tides from the Pacific Ocean is highly possible.

Atmospheric River Categories

The Center for Western Water and Weather Extremes (CW3E) has provided an explanation when it comes to the different categories when measuring the amount of rain from an atmospheric river (AR).

There are five categories-with 'AR Category 1' being the lowest and 'AR Category 5' being the highest.

The various measurements are the following:

• AR Category 1 (Weak) - the lowest AR category with substantial rainfall that can last for at least 24 hours. It is characterized to be primarily beneficial.
• AR Category 2 (Moderate) - several inches of rain can be produced from this AR category and can span for at least 42 hours. It is described to be mostly beneficial.
• AR Category 3 (Strong) - accumulation of rainfall can reach between 5 and 10 inches, enough to increase water levels along rivers. Considered as a balance of beneficial and hazardous.
• AR Category 4 (Extreme) - this mostly hazardous category of an atmospheric river can produce torrential rain for up to 14 inches and can cause widespread flooding.
• AR Category 5 (Exceptional) - the strongest category described as primarily hazardous; which can produce continuous rainfall for approximately a week and life-threatening flash floods.

The forecasted atmospheric river is under category 4.

According to CW3E, it can serve as both beneficial and detrimental in the Pacific Northwest. The rainfall from this phenomenon replenishes the West Coast water supply while triggering some of the worst flooding events in the region.

Importance in the Western US

According to a study published in the journal American Meteorological Society in 2019, atmospheric rivers are important in the western United States and other regions worldwide since it also provides a substantial amount of water supply.

An atmospheric river or an atmospheric rain is crucial, especially in the case of the western US, where the occurrence of wildfires and drought are common due to increasing temperatures that have battered the region, notably in the state of California.

In a published study in Nature Climate Change, scientists revealed the western US experienced the worst 'megadrought' for the past 1,200 years between 2000 and 2021.

They concluded that drought has been aggravated by human-driven climate change and global warming during the 22-year period.