Pacific Northwest Weather: Heavy Rain with Strong Winds Persist Across Region Amid Rare June Atmospheric River

An atmospheric river has struck the Pacific Northwest region of the United States in recent days, causing wet weather at the onset of the country's summer season. As of Wednesday, June 5, heavy rain and strong winds have persisted across the region, according to the National Weather Service (NWS). The weather system is expected to cause potential flash flooding and urban flooding.

The rare June atmospheric river has been initially forecasted by US meteorologists to bring torrential rain in the Northwest starting Sunday, June 2. However, this narrow atmospheric column carrying water vapor and moisture is unprecedented at this time of the year. According to experts, atmospheric rivers occur mostly in the western and northwestern US during fall and winter.

Under the current season, US weather authorities earlier this year have projected an above-average summer for 2024. Between June and August, scorching temperatures and heatwaves are expected to hit different parts of the nation. On Monday, June 3, NWS offices in California, Arizona, and Nevada issued excessive heat warnings for multiple cities in their respective states until Friday, June 7.

Rare June Atmospheric River Storm

The NWS office in Portland, Oregon, in late May forecasted that the potent June atmospheric river storm will make landfall on Sunday, bringing moderate to heavy rainfall until early Tuesday. However, the atmospheric river has been expected to be fueled by remains of a tropical system, and in turn, delay the wildfire season this summer season.

Atmospheric rivers are known for causing widespread flooding in California in recent years. Yet, there are also beneficial effects of these weather systems in the past, particularly between 1950 and 2010. During this period, between 60% and 74% of prolonged drought ended after atmospheric rivers made landfall, according to the U.S. Department of Agriculture (USDA).

Still, these systems bring catastrophic impacts to the environment and communities. From late December 2022 to mid-January 2023, a series of atmospheric rivers resulted in flash floods, landslides, and power outages in California.

NWS Heavy Rain Forecast

Meanwhile, a heavy rain forecast at 3:40 a.m. EDT (local time) on Wednesday has been issued not only for the Pacific Northwest but also for other regions across the US this week. According to the NWS' Weather Prediction Center (WPC), thunderstorms and "heavy to excessive rainfall" are possible from the southern Great Plains to the Northeast US region through Thursday, June 6.

The wet weather is caused by a system building up across the Western US this week. Heavy rainfall events will also spread eastward. It will affect parts of the central Appalachians, Ohio Valley, and Mid-Atlantic regions. A 'slight risk' of excessive rainfall warning resulting to flash flooding remain in effect for Wednesday, the WPC says.

The forecasted excessive rain over the Eastern US is influenced by a duo of low-pressure systems tracking the eastern half of the country, which will also bring isolated rainfall events and thunderstorms. The WPC says this weather pattern will shift into the East Coast on Thursday, potentially affecting states ranging from Maine to New York and Florida.