What is an “atmospheric river”?
FOX Meteorologist Craig Herrera shows us how these massive rainstorms that can stretch 250 to 350 miles wide and more than 1,000 miles long can be both a boon – and a bane for the West Coast .
SEATTLE – Meteorological summer begins this year in the Pacific Northwest with a shift back in time to winter as rare, back-to-back river-style atmospheric storms sweep through the region to kick off the week.
It is a tropical phenomenon fueled by the remnants of an ancient storm in the western Pacific Ocean. With deep tropical moisture available, the storm has promising potential for record rainfall and even pushes some rivers to the brink of flood stage.
“I heard June-April is coming!” the National Weather Service in Seattle published the
Some areas of light rain on Saturday will become much wetter on Sunday, as the first of two powerful storms will bring waves of heavy rain, reminiscent of a winter-type rainstorm, rather than the dry weather that would usually mark the start of meteorological summer .
WHAT IS AN ATMOSPHERIC RIVER?
Rain will increase in intensity in the northwest Sunday afternoon, with torrential rain likely overnight Sunday into Monday morning as the first atmospheric river storm heads toward the coast.
After a brief lull later Monday, a second atmospheric river storm will pass through the region Tuesday into Wednesday bringing additional rain. Both have tapped into subtropical moisture and the latest storm could even harvest some moisture from the remnants of a typhoon that slammed into the western Pacific earlier this week.
Some computer projections indicate that atmospheric river storms could reach a level 4 out of 5 on the Center for Western Weather and Water Extremes scale, which would be only the fifth time a level 4 storm has reached the region in June since 1959.
WHAT DOES A “CATEGORY 4” ATMOSPHERIC RIVER MEAN? THE SCALE AIMED TO ASSESS NATURE’S LARGEST SOAKERS
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Flood Watch is in effect for the Seattle area
About 1 to 2 inches of rain is likely around the Seattle and Puget Sound area. While this may not seem unusual for a region known for its precipitation, heavy rains are rare in June – Seattle only receives 1.45 inches on average for the entire month.
“It is certainly possible that some locations will exceed their normal June monthly precipitation during the first 3 days of the month,” wrote Dana Felton, NWS Seattle meteorologist, during Saturday morning’s forecast discussion.
Up to 2 to 4 inches is likely in the Cascades and Olympic Mountains, with some isolated areas receiving up to 6 inches of rain. These quantities could push several rivers in the region to flood stage, or even slightly above, the National Weather Service warned.
THESE ARE THE RAINEST HOURS AND MINUTES IN AMERICAN HISTORY
Rain forecast for Western Washington Sunday through Tuesday (FOX Weather)
A rare June Flood Watch is now in effect for the greater Puget Sound region, including the Seattle metro area. This is only the fourth time a flood watch has been issued by the NWS Seattle office since June 2006.
Rivers, creeks and creeks could flood even in urban areas, while the Snoqualmie River, one of the largest river systems in the Puget Sound region, could even reach minor flood stage, residents warned. forecasters.
“The flood stage of the Snoqualmie (river) at Carnation is 54.0 feet,” Felton said. “Forecasts predict the river will reach its peak at flood time. The Snoqualmie at Carnation has never exceeded 52.5 feet at this time of year.”
At these river levels, much agricultural land and several roads could be flooded, according to NOAA.
Very humid in the Willamette Valley and western Oregon as well
Similar soggy forecasts are forecast for northwest Oregon, where the lowlands of Portland and western Oregon could see 1 to 3 inches of rain and 2 to 5 inches or more across the mountains . Like Seattle, Portland averages about 1.5 inches of rain for the entire month of June.
Rain forecast in the Portland area Sunday through Tuesday. (FOX Weather)
“It is not out of the question that there could be rapid increases or even minor flooding in a few of our more flashy streams and drainages,” NWS Portland wrote in its Friday morning weather discussion, although They currently rate the chances at 10% or less. .
Other impacts include problems with agriculture and crops planted in flood plains, regional road construction projects that have already begun assuming we are outside the rainy season, and increased dangers for outdoor recreation, such as hiking, climbing and kayaking, due to heavy rain and gusty winds.
Big change to a warm and dry model a few days later?
But the return of winter could turn dramatically into summer by the end of next week in the Northwest.
Some long-range forecasts suggest a rapid change in weather conditions, which could lead to much warmer weather as a strong ridge of high pressure forms in the region.