I hope your 2021 has been happy, safe and fun so far! It’s been a very tough year for all of us. The COVID-19 pandemic has claimed too many lives; and caused too much despair and loneliness to bear. But with vaccines beginning to circulate now, it won’t be many months more before something resembling normal social life resumes.

This pandemic has definitely been a deep reminder about what is really important in life. My hope is that whatever “new normal” emerges, that people will place more value on their social relationships than before, rather than allowing themselves to become alienated in a neverending rat race.

But there is another, far more dire specter that will be haunting our news and our politics, after the COVID crisis has passed: the specter of climate change. While climate change probably played only a secondary role in Oregon’s terrible September 2020 megafire outbreak, there’s no doubt that regional fires (in general) have gotten far worse in recent years.

The main reason I moved from The Dalles to Portland two years ago, was for better cultural connections and to hang with the many weather buddies I made over the years. But climate, and climate change, were also motives. The brutally hot 2014 & 2015 summers in The Dalles were nearly unbearable for me. Expecting worse in the years ahead, I knew it was time to get out of the low desert and into the lush Cascadian forest land once again.

The Method

The official “numbers” used to categorize a town or city’s climate (average temperature and precipitation), are given for a 30-year period. Once per decade, the averages are retabulated by getting rid of the oldest decade and adding the new decade just completed. But climatological decades are not defined the way most of us think. Instead of beginning the decade with a year ending in ‘0’ and finishing with a year ending in ‘9’, the decades begin with ‘1’ and end with ‘0.’

The most recent set of data has been the 1981-2010 climate normals, which have been in use since 2011. Now it is 2021, and the numbers for 2020 are in. In this blog, I am going to show you how the numbers have changed, both for Portland International Airport (PDX) and for the Columbia Gorge Regional Airport (DLS). I’m also going to take a broader look at climate zones across both sides of the Cascades, in order to show any regional differences in the long-term trends.

PDX: 1981-2010 vs 1991-2020

Before we delve into the new numbers, let us take one final look at the old numbers, 1981-2010. This corresponds to the climate regime that I knew growing up, as well as in early adulthood. Of course I was living in The Dalles and Eugene during this entire timeframe. But our TV forecast in The Dalles always had Portland numbers on it, so I was always familiar with the general seasonal temperatures in the Rose City.

(All PDX climate data courtesy of Portland NOWData, w2.weather.gov/climate/xmacis.php?wfo=pqr)

 

A few things to point out here. At least in my lifetime, Portland has never had what we might call a “cool-summer climate.” Our numbers may look pretty anemic compared to most of the country, but July and August average highs have been in the low 80s, with August averaging just marginally warmer. At least between July 4 and Labor Day, we get a lot of days in the 80s most years, and at least a couple “heat waves” with temps in the 90s for a few days. Of course there is the occasional anomalous cool summer, like 1993 or 2011. But even those years still have a decent smattering of sunny 80+ degree days, in between the summer clouds & drizzle. (I think the fact that PNW Junes are usually quite a bit cooler than the other summer months, can fool a lot of early summer tourists, though.)

September averaged slightly warmer than June over these 30 years – another sign of the West Coast’s iconic tendency to have a later peak of summer than most places east of the Rockies. Winter, on the other hand, tends to peak early here: the coldest average daily temperature for 1981-2010 was in the 2nd half of December! That wasn’t always the case at PDX; several decades ago, early/mid January was in fact colder than December.

Precipitation follows a classic ‘Mediterranean’ pattern; with July and August as the driest months and November-January as the wettest. The ramping up of rainfall in the autumn is generally much more abrupt than the gradual drying trend in the spring. In some autumns the switch from dry to wet is very abrupt: just look at what happened in 1994!

Now, let us look at the new data for 1991-2020 for the same four parameters. To save space, I’m going to use some spreadsheet images that just show the change, and then post the 2011-2020 data separately below. That will give us a picture of how much the past decade has differed from the others.

Yes, the climate of Portland has gotten warmer! But notice that the warming has not been consistent across all months. In particular: May, July, August and December have seen big increases while February and March have actually gotten slightly cooler! January is quite similar to before. The change wasn’t lopsided enough to make January the coolest month once again, at least not in the 30-year timeframe. But December and January temps are closer together than before.

Daytime high temps have not warmed as quickly as mean temps, for the most part. Meanwhile, the nights have been warming the fastest of all. The effect seems to be strongest in late summer and early fall, just about the time that longer nights & radiational cooling are normally beginning to kick in. Could the higher CO2 levels (and possibly the stronger urban heat island), have an especially strong effect on our temps at this particular time of year???

There hasn’t been enough of a change in monthly precip patterns to note here; though December has replaced November as the wettest month. Interestingly, March has been wetter than February in Portland for a while now.

If we look only at the past decade, we see a more distinct warming trend. Wow…August is really getting toasty! May has also gone way up, while February, interestingly, has been cooler than before! And that is in spite of two historically warm Februarys (2015 & 2016). That fits into the anecdotal feeling I’ve gotten the past decade, about us getting more late winter cold than we used to. We had modified arctic air of some sort after Valentine’s Day, in 2011, 2018 and 2019 – not to mention a big early February snowstorm in 2014. I think it’s important to note that the first three years of the decade were not warm; 2011, in fact, was the coldest year at PDX since 1985! It’s as if beginning in 2014, the climate of Portland fundamentally shifted more toward the kind of temps that Roseburg has traditionally enjoyed.

As for precipitation, the one thing that really stands out are drier summers than before, at least during July & August. Oh…and March has been nearly as wet as January and November. Fun times! But there hasn’t been a huge shift toward wet or dry, overall. Slightly wetter than previous decades, though.

I think the screaming message for Portland is that the last 7 years, were much warmer than anything we experienced in the previous 33 years. Is this a sign that human-caused warming is beginning to accelerate? Now bear in mind that we’ve also had an unusually warm blob of ocean water to our west, for a significant part of this 7-year period. It hasn’t been there continuously; so I doubt that ‘The Blob’ alone explains all of our warming. On the other hand, the fact that the Blob has been as persistent as it has, makes it hard to dismiss the question of whether it, itself, is part of the whole climate change equation.

While the heat island around Portland has likely continued to grow in recent years, I doubt it’s had a huge influence on the sudden warming trend of the past 7 years, at least not near the airport.

The Dalles/Dallesport (DLS)

Technically these numbers are valid for the small town of Dallesport, which lies just across the road from Columbia Gorge Municipal Airport. There are some minor differences in the weather between Dallesport and The Dalles. But I am not well-equipped to discuss them, simply because there isn’t much reliable data on the town’s local microclimatology. Both Dallesport and The Dalles get plenty of west wind in the summertime, though in Dallesport more of that wind comes directly from the main “channel” of the gorge. In The Dalles proper, the same wind tends to come down from Sevenmile Hill and Wasco Butte to the west, both of which are near 2,000’ in elevation. (Data courtesy of NWS Pendleton NOWData; https://w2.weather.gov/climate/xmacis.php?wfo=pdt)

 

It is a largely semiarid climate, or perhaps “dry Mediterranean.” Annual precip patterns still follow the Mediterranean template, it’s just that everything is much drier than Portland at a given time of year. Summers are, of course, hotter. The winters are colder than Portland, but not really that much colder if you think about it. (Certainly not compared to places further east or up in elevation – they make The Dalles look like a banana belt in the winter!)

Unlike in Portland, July is hotter than August here. June is also warmer than September. The seasonal lag is a bit less pronounced in the summer, and there’s usually a distinct shift toward cooler nights as we move into late August and early September.

I’m not going to post the entire 30-year chart for 1991-2020 this time; just the 2011-2020 decadal charts below to really drive home the point. As you can see, Dallesport is also getting warmer; though not by quite as much as Portland Airport. In the case of Portland though, the heat island effect for 2011-2020 is probably significantly greater than 1981-1990. That’s not the case for Dallesport; the town is too small to have much of an effect. (Below I will share regional trends; which is a better way to control for heat-island effects between different weather stations.)

As in the case of PDX, the first three months of the year have stayed about the same, or even gotten slightly cooler. July, August and December are once again big months for warming. But unlike PDX, the warming is more noticeable by day than by night. The nighttime warming was almost entirely limited to May-September, plus December. Precipitation has generally gone down slightly, except for the spring and mid-autumn periods.

If we look at the 2011-2020 charts, we see some interesting trends: August was hotter than July, for once. Doubly so when it comes to daytime max temps. It hasn’t been trending that way long enough to flip the 30-year averages yet; but maybe it will next decade if August continues to outperform July for heat. Like Portland, things generally got warmer after 2014, but the shift hasn’t been quite as dramatic. And there has been a fairly significant drop in precipitation over the past 10 years.

Remember back in 2014-2015, when Portland was setting new records for warm months on a recurring basis? A lot of those same months were not records for DLS; many of the time we came out in 3rd, 4th or 5th place instead. And while PDX has seen historically unprecedented numbers of 90+ degree days in some of the recent summers, I can’t say quite the same about 100+ days in The Dalles. There were a lot of triple-digit days in the 2010s, but we didn’t break any annual records. Anecdotally speaking, it seems that more of our heat waves in the past several years, have been especially “focused” west of the Cascade crest, with strong thermal troughs and offshore flow. This same synoptic pattern isn’t quite as favorable to record heat over north-central Oregon and south-central Washington.

To sum up, The Dalles is also getting warmer. But the trend isn’t quite as dramatic as Portland. I’m not sure just how much of this has to do with PDX being closer to the influence of the Blob. As I just mentioned above, the upper-level pattern during our recent warm/hot spells also seems to be favoring the immediate West Coast over the intermountain region. The Columbia Basin also seems to have gotten quite a few “off-season” pushes of cool Canadian air in the past decade (fall, late winter, early spring). Even the windstorm pattern responsible for the September 2020 megafires, was fueled by one of these off-season Canadian airmasses to our east.

Regional Climatology, 1951-2020

There are still old-time weather geeks who remember the epic winters of the 1950s and ‘60s in the Pacific Northwest. Many of today’s airport weather stations came online during the 1940s and early ‘50s as well. Let’s look at the long-term trends from 1951 to the present, for several different regions of Oregon and Washington. (This includes the most recent decade, plus the 1981-2010 period, plus 30 years before that!) First, temperature trends for the Oregon coast (courtesy of noaa.gov/cag)

One caveat here: It is possible to make the warming trend look a little faster or slower in these charts, by cherry-picking the starting year. For example there were some pretty warm years in the early 1940s, and including these in the data might make the trendline a bit less steep – but still very much uphill. Or we could start the dataset in the mid/late 1940s, to include the severe winters leading up to 1949-50. That would make the warming trend look steeper yet.

You can see a clear trend toward warming even in the coastal regions. This is interesting, because a decade ago there was considerable discussion about whether influence of the Pacific Ocean would serve to delay the warming trend in Western Oregon and Washington. But the data for the past 70 years doesn’t seem to confirm this: coastal regions have also warmed up quickly. What really stands out here is what happened after 2006: notice how the short-term “binomial” trend curve (in green) dips dramatically below the long-term blue trendline in the late 2000s/early 2010s, and then swings wildly uphill in the mid-2010s. There was a serious “cool” cycle in place one decade ago, followed by an equally dramatic shift to warm. And 2014 and 2015 were outlandishly warm for coastal regions, a clear sign that ‘The Blob’ was making its presence known.

 

Next, the Willamette Valley region #2. It encompasses everywhere between the east slopes of the coast range and the Cascade foothills. The PDX station lies at the far north end of this zone:

Once again, a very clear warming trend. And once again we see the amplified cool cycle around the late 2000s, followed by an abrupt shift to warm in 2014. Actually the warming trend is a little less dramatic over the 70 years; +2.6 degrees F per century instead of +3.2. But still…that’s a serious amount of change, and it’s beginning to push us into uncharted territory. More to the point…the coldest year of the past three decades was 2011, which came in close to 50.0F for the region. Back in the 1950s-70s, every 3rd or 4th year was as chilly as 2011, if not even colder!

Here is north-central Oregon. It includes Hood River, Wasco, Sherman, Gilliam, Morrow and part of Umatilla County. DLS airport is not inside this zone (it’s in Washington, remember?) but it does border the northwest corner.

Interesting. The past 15 years haven’t seen quite the erratic cycles that the western part of the state has. But the long-term trend is still toward warm, and at a similar pace. One thing that stands out compared to the west side, is that the warm departures have been less dramatic from 2017 to 2020. In fact 2019 was as cold as 2011. This seems indicative of more cool/dry Canadian airmasses affecting the intermountain region, in seasons other than midwinter.

Precipitation – Climatologists love to debate just how rain and snow patterns will differ on a warmer planet. The general impression I got from the discussion was that the Pacific Northwest was expected to see a more amplified wet-dry pattern between winter and summer, with total annual rainfall increasing slightly. Here is the 1951-2020 trend for just two regions in Oregon – the Willamette Valley and North Central:

Total precip over North Central Oregon has hardly changed since 1951. There has been a modest but significant drop in total precip over the Willamette Valley over the last 70 years. Looking at the chart for the Valley, I’m sure seeing a lot more dry years after 1985, than before. There were still two ‘wet’ cycles in the past four decades, one in the mid/late 1990s and another centered on the late 2000s / early 2010s.

Since our rainfall patterns are very seasonal here, let’s divide the year into its wet (October-March) and dry (April-September) halves, just for the Willamette Valley:

Surprise! While total annual rainfall has been trending modestly down, there has been a slight increase in the (normally) drier 6 months of the year. Meanwhile the October-March season has clearly gotten drier. I’m pretty sure that July and August have been trending dry in recent years, that means the “wetter dry seasons” must be due to more rain in the spring and early Fall.

Snow, PDX and Cascades

The Dalles stopped keeping official snow records, some time around the year 2000. So it’s hard to tell exactly how their 30-year climatology for snow might have changed. But anecdotally speaking, the 2016-17 winter was the snowiest winter I have ever lived through. Basically the ground out in the eastern Gorge was white from the 2nd week of December, until some point in the latter half of February. Residual patches of snow on north-facing hillsides south of town, remained into early March. There were also heavy snowstorms in February 2014 and again in February/early March 2019, even if I wasn’t there to experience the last one. I don’t think the last decade was any less snowy than the previous three, and may well have averaged more snow thanks to that one crazy winter. But I really have no clue on specifics.

But we have plenty of data from PDX. Its snow station was moved to the NWS Portland office in Parkrose, back in the mid-1990s. That’s just a couple miles to the east-southeast of PDX, so I think it is geographically close enough to serve as a fair proxy.

To save time and space, I’m going to just show averages for the seven decades, from Fall 1950 through Spring 2020. The first winter in a decade begins in a ‘0’ year and ends in a ‘1’ year.

(Data courtesy of www.wrh.noaa.gov/pqr/pdxclimate/index.php)

Portland is definitely getting less snow than it did in the “olde tyme days,” but what sticks out to me is how little things have changed since the 1980s. This data doesn’t include the 1940-50 decade, which had three very snowy winters including the record-setting January 1950 at the very end (over 40”!!!). But it’s clear that old-timers grew up in a snowier Oregon, than my generation ever knew.

Total snowfall at PDX declined from the 1950s through the ‘80s, but then increased slightly during the 1990s and 2000s. In the 2010s it started to decline again…but even then it was just barely less than the 1980s. What’s happening here? Part of it may just be luck on our local part: incoming low pressure systems in a favorable position for Portland-area snow over the last three decades, enough to “offset” the effects of an otherwise-warming climate. Or alternatively, we may have gotten “unlucky” with snowstorm position during the ‘80s, all else equal. But I have a gut feeling that jet stream amplification may be playing a role as well. We may be on the warm side of the jet the majority of the time…but when cold air does slip down from the north, it’s still highly effective at bringing snow to the lowlands. We also seem to be getting more winter action & cold airmasses late in the season. Of the four snowiest months in the past decade, three of them were Februarys (2014, 2018, 2019). The other one was January 2017.

Tracking total snowfall in the Oregon Cascades is a little tougher. Some seasonal data exists, but most of our mountain snow climatology is instead measured in terms of the “snow water equivalent” or SWE: the amount of liquid water contained in the snowpack on a given day of the year. Here, for example, is a SNOTEL climatology graph for the Mt. Hood Test site, located just below Timberline Lodge at roughly 5,400 feet elevation:

(image credit: wcc.sc.egov.usda.gov/nwcc (NRCS site))

The dark red curve is this water year’s precipitation totals, Oct. 1 – present. The light red curve is the 1981-2010 median precip total. Dark blue is current season’s water-equivalent snowpack at the Mt. Hood Test Site, and light blue is the 30-year median. As you can see, the snowpack “normally” peaks some time between April 1 and about May 10, then rapidly begins to melt off in late May and June. For the purpose of this blog, I’m going to use the SWE (or ‘WTEQ’) on April 1 and May 1, to represent the snow season as a whole. This way I can account for total snowfall during the “core” season of November-March, as well as any “bonus” snow that comes in April.

(data courtesy of: wcc.sc.egov.usda.gov/nwcc)

Here we have the April 1 and May 1 SWE averages for each of the four climatological decades, from Spring 1981 through Spring 2020. I think it’s obvious that snowfall in the High Cascades of Oregon is on the decline. On both dates, snowpack was roughly 25% less in the 2010s than it was in the 1980s.  (Had President Biden instead been an Oregon snow climatologist, he might refer to this as a ‘Big Forking Deal’ or similar.)  It’s not a matter of the snow coming earlier or later, or melting off sooner. The local mountains are just getting less snow, period. Put a FORK in it.  And with less snow comes a host of new challenges for fish, wildlife, farmers, and fire control.

Yet Portland’s snowfall has not declined significantly since the 1980s, and I don’t think Hood River and The Dalles have seen much of a drop-off either. Why might that be?

The heaviest snowstorms in the mountains are generally associated with cool upper-level troughs that bring storms in from the Gulf of Alaska. Chilly onshore flow slams the Cascade slopes head-on, which is highly effective at generating heavy snow through the “orographic effect.” In contrast, lowland and Gorge snow usually coincides with cold air and offshore flow (east wind). This would suggest that while we are still getting chilly east wind in the wintertime, we’re not getting cool North Pacific storms the way we used to.

Thinking anecdotally, it sure does seem that we’ve had a lot of winters lately, without many of these cold troughs. Think of a bitterly cold rain in the valleys and snow in the Coast Range and Cascade foothills. It’s been quite a few years since we had a winter that was dominated by such a pattern. (There’s also the question of the ‘Blob,’ and how it might have affected snow levels in some recent winters.)

Summary and Looking Ahead

I think it’s quite clear that our overall climate is warming. So far, summers have been warming faster than the other seasons, especially July and August. But that particular trend is subject to change. It’s just possible that summer temps level off over the next decade, while the other seasons see more pronounced warming instead. We will have to see with our own eyes.

Precipitation seems to be shifting in favor of wetter springs, at the expense of summer and winter. Over the last decade, July and August in Portland have become drier than ever before. Snowfall is not showing clear decline (yet) in Portland or other lowland locations, but it is in the Cascade Mountains.

The final topic to ponder is how things will change in the next few decades. Plenty of climatologists have tried to simulate the future conditions in the Pacific Northwest – and some day soon I will probably write another blog dealing with this question. But for now, here are a few questions to bear in mind:

1. Are we on the verge of a major “snowless apocalypse” in the Cascades, or will the decline in SWE levels be more gentle and subtle? Again, I think a lot of it depends on what synoptic patterns come to dominate our winter & spring seasons in the years to come. Perhaps, in spite of a general warming trend, we still manage to get a fair number of cool storms off the North Pacific. That could at least prevent the snowpack from collapsing rapidly over the next 20-30 years.
2. Will what lowland winter weather we do get in the coming years, come “later” than it used to? It sure seems like the past decade has seen a lot more action in February, and even March at times. The current winter is following a very similar script: unusually warm throughout the entire first half, then finally turning chilly in late January and early February.
3. How will overall warming differ west vs east of the Cascade crest, in the years to come? The 2010s were remarkable in terms of how much warming we saw on the west side, relatively speaking. Perhaps this is a temporary synoptic phenomenon, driven by more West Coast ridging than before. But intermountain warming could well accelerate in the future.
4. Will we continue to see fairly “normal” precipitation patterns in spite of the warming temperatures, or will the entire Pacific Northwest be thrown into a long-term drought? We’re already seeing some pretty bad drought conditions that have popped up across the state of Oregon in the past few years, and a less extreme version in Washington. I distinctly recall the drought maps from last spring, looking pretty grim for almost all of Oregon. The droughts have generally been worse to our south and our east; perhaps an ominous sign that a drier climate regime is encroaching on our region.

In any case, this has been a VERY long discussion about the “new normal” for our seasonal climate. The topic is sure to be at the front of many weather geeks’ minds in these coming years!

…As for current weather news?  Well the 18z GFS (‘drunk uncle’) today was showing THIS for early next week:

Normally I wouldn’t put much faith in the 18z due to its antics.  But it’s only 5 days away.  So go ahead and wishcast, if you wish!

-Karl