A moisture-laden storm will sock the Northwest from Wednesday into Friday, and some areas along the Interstate 5 corridor could receive nearly a month’s worth of rain.
Published Nov. 9, 2021 10:10 AM EST | Updated Nov. 9, 2021 2:58 PM EST
This fall has featured frequent episodes of stormy weather along the West Coast, especially across the Pacific Northwest. In fact, it's been so stormy that the latest stats from the U.S. Drought Monitor show that drought conditions have been erased across western Washington.
The city of Seattle has now had two consecutive months of above-average rainfall, racking up 8.78 inches of rain, or roughly 159% of what is typically observed during that time. Through Nov. 7, the Emerald City has observed 2.42 inches of rainfall or about 178% of average through the first week of the month.
Farther south in Portland, Oregon, the same streak of above-average rainfall has been observed over the past few months as well.
While both of these cities will deal with unsettled conditions into midweek as a storm slams into the California coast, the atmosphere will quickly recharge and send a river of moisture into the Pacific Northwest later this week.
Atmospheric river events along the West Coast, similar to the one that occurred in California in late October, can bring along intense rainfall rates that persist for hours on end. While this can be great to temporarily curb drought concerns, it can also host a slew of potentially hazardous conditions.
The risks of flash flooding, river flooding and mudslides may increase across western Oregon and Washington late this week, as multiple days of rain are expected.
This next storm to target the Northwest will span from Wednesday night through the day on Friday and could tally up nearly a month's worth of rain in some locations along the Interstate 5 corridor.
AccuWeather Chief Broadcast Meteorologist Bernie Rayno said the moisture from the incoming storm could be traced all the way to the tropical Pacific.
"This is gonna be a potentially very wet system and a very warm system," Rayno said.
Because of the stormy pattern as of late across the Pacific Northwest, the ground has had to work overtime in an attempt to soak up all the moisture. With the soil moisture profile nearly saturated, the ground cannot effectively absorb heavy rainfall, further increasing the risk for flooding.
Snow levels will remain high as this storm rolls ashore. All of the fresh snowpack that has built up below 5,000-6,000 feet in recent days may be threatened because the late-week storm could drop precipitation as rain rather than snow and lead to additional flooding concerns.
Wednesday will feature somewhat of a reprieve from precipitation across the Pacific Northwest, both in coverage and intensity, as Tuesday's storm slides inland. Lingering rain and mountain snow showers will likely dot the Cascades and the northern Rockies until the next potent storm arrives late Wednesday.
The arrival of the atmospheric river and subsequent steady rainfall will begin to drench western Oregon Wednesday night before spreading inland up the Columbia River. Into Thursday, many of the same areas will continue to receive steady rain.
The firehose of moisture is expected to wobble northward into Washington through the day on Thursday, potentially expanding the flooding threat into places like Olympia, Tacoma and Seattle. After the arrival of rain into Washington state, it may be set to last through at least Friday before tapering off.
Widespread rainfall totals of 1-3 inches can be expected across the low-lying valleys of the Pacific Northwest from this storm. At higher elevations, rainfall amounts could ramp up significantly, perhaps to over a half of a foot along the western facing slopes.
While the steadiest wet weather will taper to more widely scattered showers across the Pacific Northwest this weekend, the impactful weather from this storm will be far from over.
This storm will make a cross-country trek over the course of the weekend and into early next week. Cold air will likely be in place as this storm sweeps through the Plains, Midwest and even the Northeast, possibly bringing the first accumulating snow for those in its path.
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