Heavy rain moving in could bring flooding, landslides


PORTLAND, Ore. (KOIN) – Gear up for a wet 24 hours around the Pacific Northwest (PNW) as an atmospheric river collides with Washington and Oregon.

The rain starts Monday night and it will likely continue until Wednesday morning. Satellite imagery helps show the band of low-level water vapor stretching across the Pacific to our neck of the woods as of Monday at midday.

There is no doubt that it is going to be a period of consistent rain that could lead on the side of heavy. That may push our boundaries for the next two days, leading to flooding and potential landslides. Click here for our full list of active weather alerts.

Weather models have been stepping through this system for some time now and it is likely that everything pans out as planned. That means this river of moisture that should arrive in full spirit by late tonight should supply plenty of water for the next day. You can see how the satellite image above pairs well with the weather model below. The precipitable water model is displaying a rather hefty plume of moisture, with a rather strong wind to help transport this successfully.

You can imagine that with all of this rain, coming off an already wet start to January, that we may have some problems with flooding. The National Weather Service in Portland has issued a Flood Watch for 10 p.m. Monday night to Wednesday morning at 10 a.m., which is the window of concern early this week. As the event continues on during the day, we may start seeing some vulnerable land break down and the integrity of some slopes weaken.

This will be a problem for the Oregon coast too, where some locations may see rain totals pushing 3 to 4 inches over a short period of time. Higher terrain may even hit the 5-inch mark when it is all said and done! A Coastal Flood Advisory is in effect until Wednesday at 4 p.m., rain already starting earlier on Monday for the northern Oregon coast; there are additional concerns at high tide this week with king tides in effect until Jan. 13. Wind gusts are very much possible as fronts move in and out, the strongest of the wind to the southern Oregon coast.

Here is a look at the rain totals from Monday afternoon to Tuesday night:

Some locations to note will be areas of the Columbia River Gorge and the rain totals out near The Dalles. This is going to end up being a rain event for all, but the excessive rain will likely be concentrated to the Oregon coast and areas of the Willamette Valley. You can see that Astoria and Tillamook are nearly pushing 4 inches by late Tuesday. Right now, I do believe that it’s those areas near the coast range and the northwest Oregon coast that will see the most enhancement.

Below you can find an outlook for excessive rain for today and Tuesday. Definitely take a second to look at the graphic in the slideshow for Tuesday. I took a quote from the discussion provided by the forecasters there at the Weather Prediction Center, but you can read more about the details here.

A frontal boundary pushing east into the Pacific Northwest early day 1 will accompany an initial surge of high pw values, followed by additional strengthening of the west southwesterly low level flow Monday night into early Tuesday.

Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1013 AM EST Mon Jan 11 2021

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