PORTLAND, Ore. (KOIN) – We have the most popular atmospheric river coming our direction: it’s the Pineapple Express!
It’s a plume of moisture that is coming from the Hawaii region, which is the reason for the name; however, it’s worth noting not all atmospheric rivers come directly from the Pineapple State. Rain will be in the forecast through the remainder of the week, but there will be a few windows that produce higher values. Before we get to that, you can cycle through the graphics below. That bright blue tentacle is the cue for moments of steady rain. We won’t be able to avoid the moisture, but there are going to be moments where you can expect no rain falling from the sky.
By Thursday, the atmospheric river is still trying to settle in and find a place to call home. It will be slightly farther to the north and a bit offshore. After a morning dose of rain, that river may lift and impact more of Washington. It then sinks back south on Thursday night and it will bring consistent rain with it. That is anticipated to stick around through Friday.
This is the timetable as of Wednesday afternoon. The first part of the rain forecast is expected to be light. We won’t attach to that reinforcement of moisture until Thursday. Friday may end up being the wettest day that we’ve had this fall and it should be a day that you may want to stay inside and do some work there.
Flooding near coastal rivers is possible. Usually during these events, the Wilson river out near Tillamook can push higher limits. There are additional concerns for debris flows and landslides in the areas of burn scars. Eagle Creek could be an area that will deal with some of those concerns.
A Flood Watch will be put into place Thursday at noon and it will hold until Saturday morning. You can see the extension of green in the graphic that is set below. This weather alert will impact the coast, valley, gorge, and mountains. Because of the landing spot of the atmospheric river, the forecast doesn’t appear to be as much of a concern down south to Eugene. I would still be prepared for rain on Friday as that rope of moisture settles south, but it won’t be as heavy as the northern valley and areas of Washington.
This is what the first part of the system looks like right now. Clouds are strolling in and this is going to be the disturbance that starts the party. If you focus your attention to the left of the looping graphic, you may see a swirl. That is a developing area of low pressure that is going to continue to drive a warm front to the northeast tonight. This will not be the steady atmospheric river, but it will be the appetizer to what is going to finish the week. You can see the development of a tail of showers from the cold front that is trailing the system. That is the first sign of the rain showers that are building and will be arriving later in the day Thursday.
TIMING & LOCATION
Swipe through the graphics to get a visual representation of the incoming atmospheric river. Notice the rain showers Thursday morning. That is leftover from what we have coming Wednesday night. For most of the day, the rain starts to lift to the north. If you check out the futurecast for 7:30 p.m., you can see the rain is to the north. It will hover around that section of the PNW until the overnight hours Friday. That means there may actually be dry time in the valley on Thursday afternoon. This is why the flood watch is likely not in place for those locations to the south near Eugene. The exact cutoff may change by 10 to 20 miles, but it does seem likely it should stay north of Marion county for most of the day. To reiterate, Thursday will be wetter in the morning, with a break in the afternoon.
Moving on to Friday morning, where the atmospheric river is glued in and now performing. The green stream extends from the central Oregon Coast all the way north into eastern Washington. It doesn’t plan on budging through the day. This is when rain totals will climb and this is when we may see the breaking down of some of the vulnerable terrain. You will notice in the final graphic that the rain does drop south into Benton, Linn, and Lane counties. There may be updates to the flood watch over the next two days. We will have any changes to the forecast here.
Here is a ballpark idea of the rain totals by the time we wrap up Friday. Weather models are trying to find a common ground, which seems to be in the 2- to 3-inch window. This will be the part of the forecast that will change the most over the next 48 hours. If you’re curious of some of the other rain totals, you can head to this article here.