Weekend rain to help put out Oregon wildfires

Weather

PORTLAND, Ore. (KOIN) – There is no hard date for the conclusion of wildfire season, with some years continuing well through early fall, while concluding earlier if fortunate for other years.

We currently have a wildfire to-do list that is quite lengthy. There are multiple active wildfires (or complexes) through the Cascades from Marion County on south, with the closest being the Bull Complex, which is currently over 21,000 acres and is at 14% containment. The list below is some of the notable wildfires that we are monitoring as of mid-September. There are also a collection of active wildfires in Washington outside of the Schneider Springs wildfire that are burning.

What is the best way to tackle this list of wildfires? Outside of the laborious work from wildland firefighters, we wait for Mother Nature to bring in the fall rain, and that wait may be just about over.

We are expecting a moisture-heavy system to move in this weekend, providing steady rain and soaking hours for the Pacific Northwest (PNW). The heavy rain has become more and more confident since the weekend. There will only be micro-adjustments as we approach the weekend.

There will be plenty of rain for the Cascades this weekend. The combination of a strong frontal boundary, moisture, wind, and orographic lift from the mountains, should help sustain a deep rain for the mountain range and nearby foothills. If you spent time focusing on the graphic above, you likely noticed that many wildfires that are active right now happen to be in the Cascades.

How can we be for sure that this is going to squash the wildfires? John Saltenberger, NWCC Fire Weather Program Manager, explains two criteria he looks for as the wildfire season is nearing an end:

a) Fuel moisture elevates to a point where growth of new or existing fire is unlikely. This is usually after a sustained autumn rain.

b) The date is late enough in the autumn that the combination of shorter days, cooler weather, and lower sun angle limit the potential for fuel moisture to dry out sufficiently to support fire growth or new or existing fires.

We know that we may fall under the first category this weekend, as the soaking rain settles to the valley floor. This should help the fuels around the Cascades, but it doesn’t mean it will completely terminate the wildfires.

Saltenberger recalls last September, “on September 17-18th of 2020, only 10 days after the catastrophic Labor Day fire outbreak, a soaking rain hit western Oregon. After the rain stopped, little further growth and little lingering smoke was observed on the fires in the Oregon Cascades and coast range.”

FUTURECAST

A strong southwest wind will move through the valley on Friday, as the approaching frontal boundary nears the Oregon coast. It doesn’t appear that there will be a lot of rain that moves through the valley at this time. Showers will develop for the Oregon coast earlier than the valley, with just some spotty action around Cowlitz county and potentially south near Portland. It’s more likely that we refrain from much rain until late Friday night into Saturday.

If you cycle to the second graphic, you will notice that the rain has arrived with full steam by morning. It will be as far south as the wildfire complex in Marion county and south through Linn and Lane counties. If you have any plans on Saturday morning, it will be wet and it will breezy. Grab your fall rain jackets and get the rain boots ready for use. Rain totals will be approaching some impressive numbers as early as mid-day.

This is a tentative forecast as of Wednesday, for the range of rain totals around Portland. Unless the timing is forced to earlier in the day Friday, the rain total isn’t expected to be that large until Saturday. Check out the slug of moisture that is set for Saturday. It is likely that most neighborhoods are over half an inch, with nearly an inch of rain Saturday. We haven’t had a soaking like this since June 13 (0.68 inches), but more so dating back to February where we had an event that could bring upwards to an inch of rain too. I wouldn’t be surprised if we have some record-breaking rainfall this weekend. Sunday could follow up with a few isolated thunderstorms and showers. When we have the potential for thunderstorms, we have the potential for bursts of rain that can also increase rain totals. Make sure you keep up for updates the next two days.

This type of rain will definitely prevent the drought monitor from worsening, but it won’t fix our drought in just a weekend. We are still well behind this water year (-9.47 inches), and even with a gulp of fall rain, we are going to fall short.

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