Atmospheric river flows into Lane County, though November still drier than normal

Atmospheric rivers are back in Eugene and Springfield, though modestly.

While its flow may feel like any other blustery day, atmospheric rivers bring moisture often from the tropics, rather than relying on local evaporation or storm fronts like typical rainfall. That moisture travels in a long band, like a conveyor belt in the sky, across the Pacific Ocean until it reaches land in the Northwest.

It’s a weather pattern that happens each autumn, but climate change has influenced variations in how it affects each season.

Peer-reviewed research shows that as the atmosphere warms, it holds more moisture. When strong winds drive that moisture from the ocean and onto land, it can unleash heavier, faster rainfall — like a sponge being wrung out, potentially leading to flooding.

The National Weather Service does not expect major impacts from this round of rain, which arrived Friday morning, Nov. 13, and is forecast to last through Saturday. Strong winds and power outages in the southern Willamette Valley, which often accompany the atmospheric rivers, aren’t expected.

That’s because this band of moisture is spread out from San Francisco to Seattle, rather than funneling directly into Oregon. In Eugene and Springfield, that is resulting in a weak to moderate effect from the atmospheric river, similar to one that came through Nov. 7.

Still, any rain is welcome, said Daniel Hartsock, a meteorologist with the National Weather Service.

“This is certainly beneficial rain, but the Eugene area remains well below normal precipitation for the month of November,” he said.

Much of Oregon saw below-normal precipitation in October, though September was above normal after midmonth rain dampened a parched landscape. Over the summer, all of Lane County was in some level of drought, with two-thirds of the county in severe or extreme drought as of July.

The fall rains come as El Niño strengthens in the Pacific Ocean. El Niño and La Niña are opposite phases of climate patterns, not storms, in the Pacific driven by ocean temperatures and winds.

For the Pacific Northwest, El Niño typically means a warmer-than-average winter. It’s less clear what it means for rain overall, but past very strong El Niño years have brought wetter-than-average stretches in December and January.

The National Weather Service says there is a 79% chance of a historic El Niño this season, one stronger than any previous event.

Atmospheric river flows into Lane County, though November still drier than normal

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