Tuesday, a refreshing wave of cool air for Oregon


Details for Tuesday, August 17, 2021

PORTLAND, Ore. (KOIN) – We deserve a day or two in the 70s this August and Tuesday is one of those days where we get to enjoy that.

It’s going to be one of those days where you can spend hours outside and not feel completely worn out or overheated. There may be some moments where the sun is hidden behind some clouds and you may request for it to come back out. We have a nice mix of sun and clouds, with more clouds in the morning.

A trough, which is a dip in the jet stream associated with low pressure, is moving through on Tuesday. That trough is going to invite a steady onshore flow, which should keep conditions a lot cooler. I expect daytime highs only in the mid to upper 70s for the valley. If we lean on the side of more sunshine, we may hit that 77 to 79 window. If the clouds hang around a little longer, it may be more of a mid 70s day. Regardless, it will feel cooler and you can get the windows open for that relief.

Weather models are showing broken clouds and even overcast conditions from about Corvallis north in the morning. It is also in the morning where there may be a chance for a spotty shower here or there, but many around the Willamette Valley will stay dry. That stretch of cloud coverage to the east is the leading force for this system, meaning the cooler air behind it should reach even the far eastern side of the state on Tuesday. Cooler temperatures for just about all locations compared to the last week.

That cold front has been moving in since Monday and that cold front is going to be the cause of the patchy drizzle or rain that falls Tuesday morning. The National Weather Service in Portland was timing out that front with a lot of anticipation and excitement for this cooler air to move in. I wanted to bring that up because it is that cold front that is going to offer up scant amounts of moisture Tuesday morning.


We aren’t expecting much rain in the forecast Tuesday, but it is potentially one of our only chances for rain this week (and this summer). It is hard to believe that this front is one of the few that have passed through this summer, bringing in a chance for measurable rain for a handful of locations. Most of the shower activity should stay to the north, but we can’t rule out about a 10% chance for a shower around Portland in the morning.

I would expect a few showers for the coast and Cascade foothills Tuesday morning, maybe during the commute. It shouldn’t slow anything down. I believe at best, we may have about a trace out there in the valley, in those spots that I mentioned closer to the foothills. If we happen to have some measurable rain, we will count it our day.

I must show you the 48-hour quantitative precipitation forecast for the United States. There are some locations not too far that are going to get the full force of this area of low pressure that is moving through.

Check out some of the rain totals for the Montana region. Notice there are some patchy green areas, representing 0.01 inches of rain around the coast and Cascades in this stretch of time. The real story is actually the moisture from Tropical Storm Fred. As it moves to the north, the states in the path will see moments of heavy rainfall and structural issues for vulnerable slopes through the mountains there. They have some areas forecasting 5 to nearly 10 inches of rain. Talk about a deluge!

PODCAST 8.16-22.21

We talk about the rain chances in the podcast too! Feel free to give it a listen if you want to hear a little more about how the weather has been driving our weekend activities and what we have coming up.

As far as temperatures this week? Well weather models are actually trending our temperatures down later in the week.

It looks like the massive ridge offshore that was originally expected to travel east this week, will stay offshore. We may have another round of 70 degree temperatures later in the week, too. This is the type of forecast that can really help us cool down this week. The confidence level is starting to increase for that wave of cooler air. If you were hoping for a pattern shift, this may be our time for that. In the meantime, enjoy what is going to be our first 70 degree days this week.

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