River Flooding is possible along most rivers in Southwest Washington and Northwest Oregon, as well as urban flooding.
A series of at least two, if not three, atmospheric rivers will bring periods of widespread heavy rain to northwest Oregon and southwest Washington this weekend into early next week.
The first system will also bring heavy Cascade snow for elevations above 3000 feet through Saturday evening before snow levels rapidly rise above 6000-7000 feet Saturday night. This means mountain snowmelt will also be a contributing factor to river flooding concerns Sunday into early next week as rain will be falling over a fresh snowpack.
The period of heaviest rainfall is currently expected to occur Saturday night through Sunday. Total rain amounts for the entire weekend are expected to range between three and five inches along the coast, 4.5-6.5 inches over the Willapa Hills and Oregon Coast Range, and 3-4 inches across the Willamette Valley,
Portland/Vancouver metro, and interior lowlands of southwest WA. 4.0-7.0 inches of rain is expected over the Cascades, Cascade foothills, and western Columbia River Gorge. 2.5-3.5 inches of rain is expected for central Columbia River Gorge and Upper Hood River Valley. Additional rainfall will occur early next week, however uncertainty is high regarding exact rain amounts from Monday onward.
Given the aforementioned rainfall amounts expected this weekend, river levels will be rising quickly. Most rivers across northwest OR and southwest WA have anywhere from a 20-40% chance of reaching at least minor flood stage, except for the mainstem Columbia and Willamette Rivers where the chance of reaching minor flood stage is around 5%. In fact, coastal rivers have a 10-25% chance of reaching major flood stage; this includes the Willapa River near Willapa, the Naselle River near Naselle, the Nehalem River near Foss, the Wilson River and Trask River near Tillamook, the Nestucca River near Beaver, and the Siletz River at Siletz.
To view current and forecast river stages for any river gage location across southwest WA and northwest OR, visit https://water.weather.gov/ahps2/index.php?wfo=pqr
Lastly, urban flooding is also possible this weekend, especially in low-lying areas with poor drainage. If you have gutters and/or storm drains that still need to be cleared out, now is the time. Any motorists with travel plans this weekend should also allow extra time for their commute as hydroplaning will be a risk due to ponding of water on roads.
