September 26, 2022

Was This the Driest Summer in Northwest History?

A dry Pacific Northwest in July and August is the normal state of affairs, but this year was particularly arid.

Some media outlets have claimed this is Seattle's or the region's driest summer on record.  Is that true?

Let's find out.  

At Seattle's SeaTac Airport, this summer (June 21-September 21) was the driest in a record doing back to the late 1940s (.50 inches).  2017 was right behind (.52 inches).  

What about a nearby station with a longer record (Kent), going back to 1912?  That is shown below with a trend line.  2022 was the driest summer on record but some came close in the 1925-1945 period.  The trend shows a slight decline (maybe a half-inch) over 110 years.  The very small long-term trend will turn out to be important.

What about east of the Cascades?   This is important because of the agriculture there and the frequent wildfires.   A different story from the west.  

Spokane (going back into the late 1800s) was dry but six other years were drier.

And Kennewick, also with a record going back into the late 1800s, was not exceptionally dry at all, with 29 years more arid.

So what can we conclude?  Western Washington was exceptionally dry this summer. The driest on record for many stations.  But there is only a minimal trend toward more dryness west of the Cascade crest.   Eastern Washington had a dry year, but it wasn't exceptional.

Let me stress, there is only a slight trend toward drier summers in our region.  

That is important, because if climate change is the cause of the dry conditions you would expect to see a long-term trend.  If a very dry summer like this year was caused by climate change, there would be a long-term trend towards much drier summers.  There isn't.  

What do climate models suggest?   Here at the UW we are running high-resolution regional climate models driven by a collection of global climate models.  This is the gold standard of such work.

Here is the prediction for summer precipitation (in this case June-July-August) for Seattle and Pasco driven by a VERY aggressive increase of greenhouse gases (the RCP 8.5 scenario) for 1970-2100.  Climate models suggest VERY little change in summer precipitation through 2022 for either station.  For Seattle, there is a slight decline in precipitation by 2100.  Virtually no change in the Columbia Basin.

So what should you conclude from all this?  

We had a very dry summer in western Washington.  But there is little overall extended trend, but plenty of variability that is probably natural in origin.   This is supported by climate model simulations that show little change in summer precipitation even with large increases in greenhouse gases.


Atmospheric Sciences 101

Like last year, I am teaching atmospheric sciences 101:  a general introduction to weather and climate, this fall.  You can learn more about the class on the class website.  I talk about everything from the basics of the atmosphere to weather prediction, thunderstorms, hurricanes, and local weather to global warming and climate.

I will be teaching the class in person at the UW, but will also make it available over zoom.  Thus, folks can take it remotely.

If you are over 60, you can take the class through the ACCESS program for a very nominal charge (something like $15).   Last year I had over 125 folks do so.

So if you are a UW student looking to learn about weather or a non-student interested in the topic, I welcome you to join me this fall.  My first class is on September 29th.


  1. Have your climate models been validated? Do they match the 40-ish years of satellite data? Unless they've been validated against data, they're useless for predictions.

    Boeing's flight models are always validated against flight test data. Unvalidated models are used only for predicting safe-to-fly predictions and predicting what to expect when executing flight test conditions. No one would ever rely upon them for in-service flights.

  2. I'm so glad that climate change is a hoax with no need for populations to change habits or consumption of fossil fuels. Was kinda scared there for a while.

    1. Stani. You are wrong about this. We need to work to reduce greenhouse gas emissions and move towards renewable energy sources.

    2. I think Stani was being facetious. Just a feeling I get.

      But I hope that that first storm isn't going to be rain-shadowed here in the North End. That first map in the last blog shows a rainshadow, and my other sources are backing off on the promise of rain. It's tough to flip that switch! We need a soaking...

    3. The so-called renewable energy sources can't be created without using copper wire. The Copper wire used must be virgin wire, not recycled, and requires the mining and refining of copper ore using gigantic trucks (diesel), explosives (diesel/ammonia), smelting (coal), sulfuric acid and electrolysis.

      As for the CO2 global warming hypothesis: FAIL. There's poor correlation between CO2 concentration and temperature. It's been warmer in the past then it is now. During the Medieval Warm Period, the Vikings were settling Greenland, they left after the end of the MWP when it became to cold to farm and the glaciers started advancing.

      The Roman Warm Period was warmer than the MWP. Civilization flourished until it grew cold and the barbarians came down from northern Europe. The Minoan Warm Period was warmer the the RWP. The civilizations fell after it grew cold again and the Sea Peoples invaded the Mediterranean.

      The absorption physics of CO2 show that CO2 is absorbing 87% of the available radiation. Doubling CO2 concentration to 800ppm will have little effect on temperature.

      The Earth's climate responds to ocean energy transport and to the effect of the Sun on the stratosphere. When the Sun is active, Ozone in the stratosphere energizes the jet stream and restricts heat transport to the poles, causing the Earth to warm. When the Sun is inactive, the jet stream is weak and is wavy, rather than straight. Heat transport to the poles is enhanced and the Earth cools.

    4. Mike, copper, like any other element, can be recycled indefinitely, without loss of quality as long as the chemistry is done properly. I spent the beginning of my career in electrochemistry.

  3. It looks to me like this dry spell is far from over, this 1/4 inch of potential rain coming is not enough to even penetrate 1inch in the ground and if you were to dig under tree canopy it would be zero, calling for 80's and high to mid 70's as far as the eye can later this week

  4. In some of these time series, there are a considerably large number of missing days. For instance, at Kent, there are 48 missing days in the summer of 1918 , 17 in 1920, 59 in 1920, 4and 7 in 1922. In the 1920s, 1938 is missing 10 days, 1939, 35 days, and 1940 61 days. I haven't bothered to look at the other sites.

  5. Obviously the very dry summer was mostly natural variability. However it is worth noting that measured as a percentage Kent summer precipitation has decreased by about 15 percent over the past 110 years. I think that is a significant trend.


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