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Atmospheric river to slam Seattle, Portland metros with steady rain
Flood alerts are in effect in the Northwest as rare June atmospheric river storms are set to slam the region starting Sunday. FOX 13 Seattle Meteorologist Abby Acone joined FOX Weather on Sunday to provide more details on the upcoming messy weather as we start the new workweek.
SEATTLE – Meteorological summer begins in the Pacific Northwest this year with a time warp back to winter as rare back-to-back atmospheric river-type storms sweep through the region to kick off the new week.
The storms are being fueled by the remnants of a former tropical storm in the Western Pacific Ocean. With deep tropical moisture available, the storm has a promising potential for record rainfall and even pushes some rivers to near flood stage.
"I heard June-uary is coming!" the National Weather Service in Seattle posted on X.
Wet weather began Sunday as the first of two potent storms brings waves of heavy precipitation, reminiscent of a winter-type rainstorm, rather than the dry weather that would usually kick off the start of meteorological summer.
WHAT IS AN ATMOSPHERIC RIVER?
Rain increased in intensity across the Northwest on Sunday afternoon, with drenching rains continuing into Monday morning as the first atmospheric river storm heads inland from the Pacific Ocean.
After a brief lull later Monday, a second atmospheric river storm will push through the region from Tuesday into Wednesday with additional rain. Both systems will tap into subtropical moisture, and the latter storm may even harvest some moisture from the remnants of a typhoon that had been in the Western Pacific earlier this week.
Some computer forecast model projections indicate the atmospheric river storms could reach a level 4 out of 5 on the Center for Western Weather and Water Extremes scale, which would only be the fifth time a level 4 storm has reached the region in June since 1959.
WHAT DOES A 'CATEGORY 4' ATMOSPHERIC RIVER MEAN? SCALE AIMS TO RATE NATURE'S LARGEST SOAKERS
Flood Watch is in effect for Seattle area
About 1-2 inches of rain is likely around the Seattle and Puget Sound region. While that might not seem unusual for an area known for its rainfall, heavy rain is rare in June – Seattle only averages 1.45 inches for the entire month.
Up to 3-5 inches is likely in the Cascades and Olympic Mountains, with some isolated areas seeing up to 6 inches of rain. Those amounts could push several area rivers up to, or perhaps even a little over, flood stage, the National Weather Service warned.
THESE ARE THE RAINIEST HOUR AND MINUTE IN AMERICAN HISTORY
A rare June Flood Watch is now in effect for the greater Puget Sound region, including the Seattle metro area. It's only the fourth time a Flood Watch has been issued by the NWS office in Seattle in June since 2006.
Rivers, creeks and streams could flood even in urban areas, while the Snoqualmie River, one of the larger river systems in the Puget Sound area, may even reach minor flood stage, forecasters warned.
"The flood stage for the Snoqualmie (River) at Carnation is 54.0 feet," NWS Seattle Meteorologist Dana Felton said on Saturday. "The forecast is for the river to crest right at flood stage. The Snoqualmie at Carnation has never been above 52.5 feet this time of the year."
At those river levels, much of the farmland and several roads may flood, NOAA says.
Very wet in the Willamette Valley and western Oregon, too
A similar soggy forecast is in store for northwestern Oregon, where the Portland and western Oregon lowlands could see 1-3 inches of rain, with 2-5 inches or more across the mountains. Like Seattle, Portland averages just around 1.5 inches of rain for all of June.
"Probabilistic river guidance shows less than a 5% chance of any of our mainstem rivers flooding due to this event," the NWS office in Portland said in its Sunday morning discussion. "There will be significant rises on some, but flooding is not anticipated. While mainstem rivers are not expected to flood, smaller creeks and streams may be a different story, especially in recently burned areas."
The NWS said there may also be debris flows in recently burned areas due to heavy rain.
Other impacts include issues with agriculture and crops planted in the floodplains, regional road construction projects that have already begun assuming we're outside the rainy season, and increased dangers to outdoor recreation such as hiking, climbing and kayaking, due to heavy rain and gusty winds.
Big shift to hot and dry pattern days later?
But the winter throwback could take a radical shift into summer by the end of this week in the Northwest.
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Some long-range forecasts are suggesting a rapid change in the weather pattern, bringing in the potential for much hotter weather as a strong ridge of high pressure builds into the region.
