PORTLAND, Ore. (KOIN) – One of the perks of the PNW is being able to enjoy the summer without much rain to hold you back. As summer starts to wrap up, then we start to see the rain picking back up.
The average rain amount for Portland in September is triple the amount of August. The stubborn high pressure of summer is slowly pushed south and the wavy jet starts showing more signs of cooler air and more rain. We will be more than halfway through the month by the time we reach the end of the week. Temperatures are going to start to feel more like fall, but the rain hasn’t shown up yet. Scant amounts have reached the valley floor in the last few days, which concluded our 67-day stretch of no rain in Portland.
When is the rest to follow?
On average from 1991 to 2020, Portland picks up around 1.5 inches of rain. That usually comes in the form of a handful of light rain events, and then an additional hand of moderate to even at times heavy showers. You can see how that breaks down in the graphic below. On average we usually have at least one day that picks up a half an inch of rain or more.
Last September we finished the month with nearly 4 inches of rain. You may be thinking, there is no chance that we end up with anything close to that based off our current situation. Well, we actually have more rain at this time than we did last year. September 2021 had nothing but a trace of rain until September 17. We then had two events that brought in over an inch of rain, and the rest is history. That means we can’t rule out a soggy finish this month. We have had an above-average rainfall in September going back to 2016.
Will we do it again? Right now, there are no signs of any major moisture coming through our neck of the woods. If you watch the precipitable water motion graphic below, you will see some light blue try to penetrate the region closer to Saturday, but it’s not going to be enough to produce a rain event worth talking about. We may not see anything significant through the weekend. That would put us closer to the week of September 19, which would leave us 11 days to snag upwards of 1.50 inches of rain to reach the 30-year average.
ALTHOUGH NO RAIN, STILL SOME BENEFIT
There is definitely some good news to our cooler air mass, regardless of the lack of rain. We are seeing lower temperatures and higher relative humidity, which allows for major progress for the wildfires in the overnight hours. It at least helps prevent a scenario where growth will get substantially worse. The overnight hours have allowed for relative humidity around the central Cascades to jump to at least 80% and then in the afternoon it drops but not to the levels that require any alerts. The higher the relative humidity, the better for transporting moisture to fuels.
Here is an image of what could be calculated as hotspots from the Cedar Creek Fire. Progress has been made since the east wind helped bloom the wildfires on Friday and Saturday of the weekend. Currently, the Cedar Creek Fire is at 92,548 acres, creeping up to what would be the second 100,000-acre “mega ” wildfire of the season.
However, with the type of conditions out there now, this should help momentum swing in the other direction as conditions help moderate fire activity.
