Conditions remain warm and dry; burn bans through Wednesday


PORTLAND, Ore. (KOIN) – No rain to speak of as we start the week and quite frankly we could use some.

We’re currently on a dry stretch here in April, where we haven’t had measurable rain in eight days. It’s not a record, but we have at least four more days before we start to increase the chance for rain in the valley, which will put us at around 12 days or so. The record is 26 and we won’t be close to that (thankfully). That does tell you that we can have some years in April where it is more famine than feast. Right now, we are currently at .09 inches of rain for the month. That is pretty much just a splash and dash type of rain event (in fact it was two short-lived rain events earlier in the month).

That being said, it’s going to continue to be dry for most of the week, since a ridge of high pressure that was around late last week and through the weekend will redevelop a bit to the west of us. Just being on the fringe of that high pressure will keep us under the spell of dry and warm weather. It will start to break down by Friday.


Unfortunately, the dry conditions and the risk for fire spread still exists for the early part of the week. Clackamas Fire decided to extend their burn ban through Wednesday, with a reevaluation coming on Thursday. Although it won’t be as warm and windy as late last week, the conditions are still holding. There have been grassfires through the weekend and even a few to start the week already. Conditions improve this weekend.

You may have seen this graphic over the weekend while watching KOIN 6 News, but it is just a quick idea of what is needed for combustion and fire spread. The three ingredients for a fire: heat, oxygen and fuel. With unseasonable temperatures well above average (10-20 degrees), we have heat around. The oxygen is going to come from the wind and the fuel is the dry vegetation (low relative humidity). This week, we bring the heat down, the wind will not be as prevalent; however, the fuel is still dry.

Over the weekend, the relative humidity was down in the teens and lower 20s. We also had temperatures into the lower 80s, but with highs topping in the 70s this week, you can expect those numbers to be a bit higher. As temperatures goes up, the relative humidity will go down. This is why it is relative and at night the humidity level goes up as temperatures drop. You can see that this afternoon, the wind is coming out of the east and the relative humidity is expected to be in the lower 30s. It’s likely that we dip to the 20s this afternoon. That is low in general, especially for April. This is why the fire concerns remain in place. If you look over to the Yakima Valley, you can see that the relative humidity is much lower in the drier areas of the state.

It’s not often that we have such a long stretch of 70-degree temperatures in Portland, but we will keep it going until probably Friday (potentially cooler Thursday). We’ve been at 70 or above since April 14, so we may go on a streak of eight days. Just a reminder that we should be down in the lower 60s, closer to 62 degrees. These lower to mid-70s is the end of Spring, late June temperatures.

Finally, when it’s dry, breezy and spring, we have pollen to worry about. This week continues the stretch of over-the-top allergens across the region.

If you’re allergic to tree pollens, this will not be your week. We had high levels all last week with the weather conditions and we do not improve this week. It’s tough to enjoy the outdoors and do the yard work but then have the allergens to battle. There should be improvements come this weekend as rain chances pick up. Good luck out there!

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