Soaking ahead this weekend in Pacific Northwest, but dry in some unexpected places

It’s raining again...

After 3 mainly (or all) dry days, the rain is back this evening. I had just transplanted a bunch of veggies and flowers today hoping for some gentle evening rains. Now I see I’ve picked up over .75″ in less than two hours at home! That’s a big excessive... PDX has already seen another 1/3″.

Somehow we still can’t get 4 consecutive dry days. In fact only once since early April have we seen 4 of those days. Yet in January & February we had some nice week-plus stretches!

Since April 1st, Portland has seen 48 days with some sort of measurable rain, that’s about 2/3 of the days, only topped by the very wet spring of 2010

WHAT’S AHEAD?

We’ve got a relatively strong (for June) atmospheric river aimed right at Oregon and SW Washington this evening. An atmospheric river just means a “river of moisture” that flows along in the low-mid atmosphere. It’s not a “storm” or “event”. In general it means significant rain is more likely than elsewhere. If everything works out just right (or wrong?) heavy or flooding rain can be squeezed out of that atmosphere. That can include the “river of moisture” running into mountains. That will be the case the next 2-3 days in our region. One way to measure the strength of the moisture transport is IVT or Integrated Vapor Transport. You can see we are right under the bullseye this evening

It’s weaker, but still aimed at Oregon tomorrow at 8pm.

Then notice it really falls apart Saturday afternoon for more typical showers across northern Oregon and southern Washington. More solid rain is likely across the central/southern half of Oregon

How much rain might we see between now and Sunday afternoon? The past two weekends models have generally overproduced rainfall for the valleys, but were okay in the mountains. Our fresh GRAF model shows 1-2″ in the valleys and 3-5″ in the Cascades. Seems like around 1″ would be most likely in the valleys based on recent experience.

You may notice two other items. The northern Oregon Coast will likely be the driest spot this weekend! Same with SW Washington and up toward Seattle. The other is a very wet northeast Oregon again! Pendleton, La Grande, Joseph, and John Day will all see plenty of rain through Sunday. So wet...

GRAND FLORAL PARADE

It’s not looking so bad Saturday morning/midday in Portland. Just a few scattered showers here and there, definitely not a soaking.

ANY SIGN OF A CHANGE?

Here’s the biggie: There’s no sign of a change into “normal” warm & dry summer weather through at least the 20th. It’s obvious this wet late spring is morphing into a wet early summer. Temperatures have been about normal so far this month which has been nice. But we’ll turn cooler Sunday through Tuesday. Why does this continue? Because we’re not seeing a typical area of high pressure push the (weak) June jet stream north into Canada and SE Alaska. That’s what often happens in June; fewer weather systems moving through = drier and warmer. What we’re seeing right now is more like April or early May, although warmer since it’s June. A great animation here shows the “dip” in the upper-level flow through the next 15 days. This is from the ECMWF (Euro) model. Note the anomaly does weaken a bit in the 2nd week...we’ll see.

Until I see a warm anomaly over us, it’s fair to say the occasionally wet weather will continue. Temperatures will likely turn a bit cooler than normal as this pattern continues. That’s because “normal” temperatures rise quite a bit the 2nd half of June. Add about 5 degrees to all the numbers below. That gives you lots of days between 68-78 degrees, just like what we’ve been seeing lately.