PORTLAND, Ore. (KOIN) — We’re easing into the fall season this year, with our first attempt at bringing in some rain expected Wednesday.

We have a mid-latitude cyclone to the west that will toss a cold front across the Willamette Valley. You can see the cyclonic flow spiraling around the area of low pressure in the image to the right. The front edge of this disturbance will impact the morning commute Wednesday.

There will be a dry slot that will show up in the afternoon, followed by additional rain from the core of the event. We will paint that arrival in the slideshow below.

This will be Portland’s first system of the fall that will bring in measurable rain. That goes for most locations across the state as well.

TIMING AND WHEREABOUTS

Rain is expected as early as 2 to 3 a.m. on the Oregon coast. I have gone and started the slideshow below at 8 a.m. to show the morning drive in. There will be rain in the Willamette Valley and up through southwest Washington by either sunrise or shortly after. That front will not only impact the Portland metro area, but it will also reach the folks down in Corvallis or Lebanon. Expect showers to reach Corbett and locations east of Portland around this time as well. Moisture will spread into the Cascade foothills through the morning.

There will be a moment in the day when the clouds depart for a brief moment. The early afternoon is expected to be mainly dry. That decaying front will reach areas just east of the mountains. This may bring in some light showers for areas like The Dalles and Goldendale. Anywhere from around lunchtime to 4 p.m., we are likely going to see a dry slot or lull in the action over the Willamette Valley. That does not mean we are finished for the day — the second wave of moisture will start to approach the Oregon and Washington coast at this time.

The showers will return by the evening commute and they will remain scattered in nature by night. This goes for most, from Hood River, west to the Oregon coast. This is due to the area of low pressure crashing into the state of Oregon. This will help generate more showers as the lift is enhanced late Wednesday night. This may actually be when we gather the most of our rain from the event.

KEY TIMING

  • Morning commute showers for the Portland metro area.
  • Afternoon break, potential for sunshine and blue sky.
  • Dinner showers return to the Willamette Valley, with scattered showers at night.

HOW MUCH RAIN?

Weather data continues to increase the amount of rain that is expected for Portland and nearby communities. This will be a two-day system, with the brunt of the event occurring on Wednesday. There may still be some lingering showers come Thursday. This will be enough rain to get the ground wet and to slow down travel. If you have kids who started driving in the summer, they haven’t had this type of rain to drive in. Make sure they are ready for potential slick conditions. Check the windshield wipers too!

This event will likely bring closer to a quarter of an inch of rain. There will be some variety with some locations picking up less. One weather model is projecting a larger rain total of over half an inch. Based on the evolution of this system, it is more likely that we fall on the lower end.

This is indeed a little later than some of our recent measurable rains that occurred in September. Most years we tend to see that first noticeable rainfall around mid-September. The last time we did collect a quarter of an inch of rain was June 9 and then we followed it up with a massive soaking on June 10 of 1.42″.

We aren’t expecting a system that significant, but it will get the ball rolling.