PORTLAND, Ore. (KATU) — The latest atmospheric river was a record breaker in many ways. But it also highlights why these systems are important for the Pacific Northwest.
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Lower-end atmospheric rivers bring rain and wind while helping build the mountain snowpack. When they stay weaker, they can boost snow levels without causing major problems like flooding or landslides.
This most recent storm was moderate. Even so, we saw both the benefits and the impacts.
Several cities recorded daily rainfall records. In the Cascades, the snowpack received a much-needed boost. But atmospheric rivers can also create dangerous conditions.
Several avalanches were reported on Mt. Hood, and a few local rivers briefly flooded. Fortunately, the flooding was short-lived.
Atmospheric rivers are responsible for about 25% to 50% of our annual precipitation. They play a major role in building snowpack and helping break drought conditions.
Over a three-day stretch, Portland received about 75% of its average monthly rainfall.
Higher elevations saw even bigger totals. Several feet of snow fell in parts of the Mt. Hood area. The Red Hill SNOTEL site on the north side of Mt. Hood recorded 9.7 inches of snow-water equivalent and an impressive 97 inches of snow.
The snowpack is still well below average, but this week’s snow will help.
Even with the recent storms, nearly every Oregon basin remains below 50% of average snowpack. The Mt. Hood basin has climbed to about 42% of average.
Why we say “atmospheric river”
I’ve seen a lot of comments recently about the term atmospheric river. In some of my Morning Minute posts and a video I shared Wednesday, people asked why meteorologists don’t simply call these storms a Pineapple Express.
Here’s the reason.
All Pineapple Express events are atmospheric rivers — but not all atmospheric rivers are Pineapple Express events.
A Pineapple Express specifically refers to moisture that originates near Hawaii. Many atmospheric rivers that affect the West Coast have that connection, but not all of them do. That’s why meteorologists use the broader term.
The difference between an atmospheric river and a cold front – Storm Tracker 2 Weather graphic
“Isn’t it just rain?”
I’ve also seen comments suggesting meteorologists are “fear-mongers” and that these storms are “just rain.”
Yes, it rains a lot during winter in the Pacific Northwest. That’s when we receive most of our precipitation.
But atmospheric rivers can deliver a month’s worth of rain in just a few days. A typical cold front might bring around an inch of rain and move through fairly quickly. Atmospheric rivers can last longer and deliver significantly more moisture.
Meteorologists are not trying to create fear. Our goal is to help people understand what’s happening and what to expect.
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When conditions could have a major impact, it’s our job to share that information. That’s also why weather alerts exist — to give you time to prepare and stay safe.