What a fun weather day for June! In the Portland Metro area there were heavy thunderstorms with dime-sized hail in places, and even reports of a minor tornado in East Vancouver. Here in The Dalles though, the big change has been a sharp chill in the air. Today’s high was only 68 degrees, a full 10 degrees below normal for this time of year. By 8pm the temperature had dropped to 55; we were about as cool as the normal LOW temp and the sun hadn’t even set yet!

Today’s and yesterday’s soaking rain west of the Cascades and in the heart of the Gorge, ends what has been a historic springtime dry stretch. Portland reported only a little over a quarter-inch of rain for the entire period from April 16 through June 7, and during this seven-week stretch The Dalles saw only 0.03″ ! Yesterday was also The Dalles’ first measurable precip in exactly one month.

Of course by “springtime” I am using Pacific Northwest reckoning; where spring is taken to linger well into June most years. Meteorologists, by way of arbitrary convention, define spring as the whole of March, April and May. How did it measure up this year?

First of all….May 2018 was a new record warm month for The Dalles. We blew away the old record from 1958 by an incredible 1.7 degrees F, setting a new temp of 67.4. That’s fully 6.6 degrees above average, and every bit as warm as a normal June! The averaged high was 80.2 and the averaged low, 54.6.

The largely summer-like May means that, despite March and April being quite close to normal, the spring season as a whole will end up significantly warmer than historical norms. We can look at detailed climate history using the NCDC’s nifty “Climate At A Glance” charts. Here is what springtime has looked like over the past 120 years, in north-central Oregon:

Several things stand out here. First of all, there’s no doubt that spring has been trending warmer over the long term; averaging about 0.15 degrees F per decade. This trend is expected to accelerate in the coming decades, as accumulating carbon dioxide levels cause still more heat to become trapped in the atmosphere. That said, the long-term warming trend has come in spurts and lulls. Notice the green curve in the graph above; this measures the short-term trend by means of a 9-year binomial filter. As you can see we had warmer springs in the 1930s, cooler springs throughout the 1950s/60s/early ’70s, then warming up again beginning in the 1980s.

But the one thing that really stands out to me are the past 10 years or so. Notice how the green curve becomes extremely ‘amplified’ at the right side of the graph. This indicates a very pronounced cycle of cool springs, followed by a flip to warm springs a few years later.

Let’s review where we’ve been recently:

The springs 2008-2011 were all very cool by modern standards, and generally more wet than dry. In particular, Spring 2011 was the coldest in 36 years, with all three months way below normal in our region.

Spring 2012 was about average by long-term standards, but still somewhat cool by ‘modern’ standards.

Then 2013 & 2014 were each a little bit warmer, though still not historically warm.

Finally, in 2015-2016, I think it’s safe to say that “all hell broke loose.” In 2015 both March and May were extremely warm, while in 2016 April was record-warm while March & May were somewhat warm. That was enough to make them the 5th and 3rd warmest springs in north-central Oregon history.

While 2017 and 2018 haven’t been as warm as the two years before, we still haven’t seen a return to cool springs by either long-term or short-term standards. So to sum up, the last decade we’ve seen a major shift in the character of our spring weather – from raw and chilly to extremely warm and dry.

At the same time that it’s gotten warmer, our spring weather has also trended wetter in this region:

There have been short-term wet and dry cycles throughout. But we haven’t seen quite as pronounced a shift in moisture in recent years, as we have in temperature. Despite the 2nd half of Spring 2018 being historically dry, the first half was actually wet enough to bring seasonal totals very close to normal. Our wet start to spring is one main reason why our fire season isn’t already raging at full speed. It’s still starting very early, just not as early as it could have been…

One final point: Spring has warmed more quickly here than it has in the Willamette Valley. Check out this graph, with only 0.10 degrees of warming per decade:

Of all the places in the state, the south-central and southeastern zones have warmed the fastest, over 0.20 degrees per decade.

I’m 98% confident that our springtime temps will continue to trend warmer in the decades ahead. What is less clear is whether it will also be wetter in the future. The general idea is for Pacific Northwest winters to become warmer and wetter, but we’re not too sure whether the moisture will bleed over into spring or not. And the recent cycle of wet springs may have little to do with global warming; many of them occurred in relatively cool seasons!

In any case…enjoy the break from our unseasonable warmth…I’m sure summer weather will be back before we know it!