Small window of dry time before heavy rain arrives


Details for December 16, 2020

PORTLAND, Ore. (KOIN) – After a wet morning on Tuesday, we should start the day dry Wednesday. However, heavy rain will move in later in the day. It’s going to be a day that you want to do things early and maybe prep for little travel or outdoor time by the afternoon and evening.

By 8 a.m. we are still refraining from the rain. It should start pushing the Oregon coast shortly after, by late morning. This is going to be your dry window for the day inland. That ridge transitions east and our next area of low pressure coordinated with the trough will bite into the Pacific Northwest (PNW).

As that front moves in our direction and the rain develops around here, the wind is also going to increase in intensity. Just like most December storms it will gust for the Oregon coast a bit more than what we have going on in the valley. We may see wind gusting to the 40 mph range for the coast and I wouldn’t count out the 30 mph range in the valley. Not only will the morning be dry, it won’t be nearly as windy.

Moisture is targeting the whole PNW, with the heaviest likely for the Oregon coast.

We can use this weather model below to determine the level of intensity and the general area of concern. Stronger wind and plenty of precipitable water to be transported in our region. Wednesday evening will be our wettest moment of the week probably. This event will help bolster our rain totals for the month, which is needed because we are currently below average.

Below is an image of the United States at 4 p.m. Wednesday. We have two systems at opposite ends of the country. Ours will bring in mountain snow and valley rain, while that system is going to create snow to the north and warmer conditions south of that low. By late tomorrow afternoon, areas like Baker City are probably still dry, with showers starting to increase for Pendleton. Most of the moisture, as you can tell from the conversation above, will be for the coast and Cascades.

It looks like we will probably finish off Wednesday and Thursday around .75 inch of rain in the valley. Totals are going to be higher for the coast and mountains.

Those of you in southwest Washington, around the Cowlitz valley, should see higher totals than communities south in Oregon. This is a typical December system that brings in rain, breezy conditions and mountain snow.

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