Atmospheric River Update as Rainfall Smashes 71-Year-Old Record

A late-season atmospheric river brought enough rain to Hoquiam, Washington, to shatter a 71-year rainfall record on Sunday.

The moisture-laden storm arrived on Sunday and is expected to continue dumping rain on the Pacific Northwest through Tuesday. This winter, the West Coast faced a slew of atmospheric rivers that caused devastating floods and landslides. The storms also brought a deluge of rain that supplemented California lakes and rivers, helping eliminate the state's drought.

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Atmospheric rivers are a "long, narrow region in the atmosphere—like rivers in the sky—that transport most of the water vapor outside of the tropics," according to the National Oceanic and Atmospheric Administration. In the United States, the storms typically are seen during the West Coast wet season in the winter.

The National Weather Service (NWS) office in Seattle warned that despite summer's approach, an atmospheric river-style system would bring foul weather to Washington over the weekend. As of early Monday morning, data revealed that Sunday's rainfall was heavy enough in Hoquiam to make it the city's wettest June day on record.

"24 hour rainfall ending 4 am," the NWS office in Seattle posted on X, formerly Twitter. "Daily rainfall records were broken Sunday in Seattle 0.65" (old record 0.48" 2001), Olympia 1.08" (old record 0.68" 2010) & Hoquiam 1.87" (old record 1.35" 1962). The 1.87" at Hoquiam was the wettest June day on record. Records started 1953."

NWS meteorologist Harrison Rademacher told Newsweek that the heaviest wave of rain occurred on Sunday night, although rain will continue in the Seattle region for much of Tuesday.

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The storms continued to move inland on Monday, sparking a slew of weather alerts in Washington, Oregon, Idaho and Montana. The NWS warned that heavy rain and strong winds were ongoing in the region. Flooding stretched as far east as Montana by Sunday evening, prompting meteorologists to warn of the impacts through Monday night.

"Minor flooding in low-lying and poor drainage areas," the NWS office in Missoula said. "Rises in small streams and creeks. Ponding of water in urban or other areas is occurring or is imminent. Localized rock and debris on prone roadways is expected."

NWS meteorologist Trent Davis previously told Newsweek that late-season low-pressure centers are moving into the Pacific Northwest, funneling a "train of moisture from the subtropics." He said that the system is uncommon for this time of year.

"It's a little late in the season," he said. "They can happen, but they tend to be late fall to mid-winter."