PORTLAND, Ore. (KOIN) – Summer brings the sunshine and warm temperatures, fall shows up with showers and wind, winter is known for soaking rains and snow — but spring, well those months can bring just about anything.

However, the month of May has been quite dry for most of the last decade. We have to go back to 2013 for our last wet May year (4.75 inches). We have been below average each May since then! Not only have we been quite dry, but we have also had a few top five driest Mays on record. It’s not the type of weather you want in the Pacific Northwest (PNW) leading into the dry summer months.

2021 had the driest spring on record. However, conditions have been nearly the complete opposite compared to last year. It’s been cooler, wet, and the mountain snow continues to come. Just what the doctor ordered. Hopefully, the prescription includes May. The 30-year average (1991-2020) for rain in Portland, during the month of May, is 2.51 inches.

There is some good news for us in Portland, although not necessarily the whole state, because we may be trending towards a wet forecast for the northern Willamette Valley this year. That doesn’t mean we won’t have plenty of dry time to be outdoors for yard work, but we will have a chance to reach our average rainfall and potentially a little more over the top.

Check out the May precipitation outlook for the month. This is provided by the Climate Prediction Center (CPC). The way the storm track is playing out, we may have more opportunities for wet weather from Washington south to the northern edge of Oregon. Unfortunately, areas that are already really dry in southern Oregon and northern California, may miss out on the deeper moisture. Of course, this can definitely play out to be slightly off. We will be hopeful that more of that moisture tracks south to other portions of the state.


There is one thing that is certain: we are going to have some rainy moments later this week.

We have two systems that are expected to impact the whole state on Thursday and Friday. Showers are anticipated to hold for the weekend too. I’ve gone ahead and pulled the forecast rain total from one weather model through Sunday. I’m going to go out and say that it is likely it is overplaying the rain totals across the board. The arrival of each system is favorable for rain south of Portland into areas of the state that need moisture. It’s just likely that we see a little less moisture than the weather model is expecting. I’m basing that off of ensembles, that are taking many model runs into consideration.

What we do know is that it will be wet near the end of the week. This type of moisture will really catapult our monthly total if it is to play out. Even if we see 50% of the rain that the weather model advertises, it will be more than we had all last May and it will put us in position for success. What I am most encouraged about is the rain totals for central and northeast Oregon. That type of moisture will be extremely helpful. April was crucial in the support of our mountain snow. May holds the potential to be immensely important too.


You may suspect that with May showers comes some cooler temperatures. If it’s anything like April, that will be the case. The CPC is also projecting a chance for cooler weather across the full PNW this month. That generally is the case as each short wave and trough that moves through the region is cool. That cold air supports unstable weather and rain. That keeps us cool during the day. That will also help keep the mountains cool. Preventing a quick melt for the mountain snow. Again, this is the type of weather that keeps the early approach of wildfire season at bay (if we are fortunate).

Here is a general idea of the upcoming pattern for the Portland area. We will have a warm day or two, but there is a stretch of cool days coming. Signs are pointing for a warm and dry second week of the month. You can see that trajectory in the graphic below. If we do end up with all those 50-degree afternoon temperatures, it will be something we didn’t see once last year.

Check out some of the numbers from last year and you can also see the frequency for temperatures above and below 50 degrees. May was cooking at times last year. There were more 80-degree highs than 70-degree highs. There were zero 50-degree highs. That isn’t out of the ordinary, because temperatures are at 60 degrees or more 81 percent of the time. It’s not often that the high temperature stay below 60 in the month of May. Well, we have a handful coming our way this year. Expect our May to feel a bit different this time around.

If you swipe to the next graphic, you will see when our first 80-degree day typically is. Last year it happened on April 17 (84R), which ended up being a record high for the day. We are still waiting it out this year and we do not have an 80-degree temperature in the forecast just yet. On average, it’s around the second week of May that we start to bring that type of warmth into the picture.

I would be prepared for an 80-degree day in the near future, although, there have been years it hasn’t shown up until June.