September 20, 2017

The Driest Summer in Seattle's History

I am now entirely confident in this. We are going to break a major record in two days:

The driest summer in the history of observations at Seattle-Tacoma Airport.

And we are not simply going to beat the record, we are going to smash it.

Let me give you the numbers.   Logan Johnson, head of the NWS forecast office in Seattle, provided these number for the driest calendar summers (roughly June 21st-Sept 21st) at Seattle-Tacoma Airport:

1988 1.28"
1987 1.33"
2000 1.36"
1990 1.39"

Seattle-Tacoma Airport records go back to 1945-- so over 70 years!

As of noon today (Wednesday June 20th), Seattle-Tacoma Airport has received only .50 inches of rain. LESS THAN HALF of the previous summer record.  And most of the rain is over for a while.

According to the latest forecast model runs, it is possible that we could get a few sprinkles today, but nothing of any significance.   Here is the latest NWS SREF (short-range ensemble forecast) that show the cumulative precipitation prediction at Sea-Tac for a number of model runs starting 5 AM this morning.  No model run provides enough to threaten our record (most produce a few hundredths of an inch).

Folks--we have this in the bag....the driest calendar summer in Sea-Tac Airport history.  

Here is a plot of the observed (purple) and normal (blue line) precipitation at Sea-Tac.  We are about 3 inches behind for the summer!
Another way of appreciating our dry conditions is the following figure, showing the percent of average precipitation since June 21st.  Most of Washington State is below 25%, with some below 5% of normal.

Why have we have been so warm and dry this summer?  The same reason the eastern U.S. has been cool and wet:  an anomalous upper level wave pattern, with high pressure over the west and low pressure over the east.   This is illustrated by the upper level height anomalies (difference from normal) for 500 hPa (about 18,000 ft) for the past 90 days.
The yellow/orange colors indicate higher than normal pressures/heights. Blue the opposite.

Some folks will get upset with me for saying this, but there is no reason to believe that such a pattern has anything to do with global warming.


  1. Cliff, I love your site and recommend it to all my weather-interested friends. Sane science and weather. What's not to love? I just wish you spent a bit more time on us folks down in Portland, where it's also been a very dry summer (as you know). Sounds, however, like we've had a bit more rain the past several days than you've had in Seattle. (We're enjoying thunder and a massive cloud burst right now as I type.) Given the rain this past week, I'm not sure Stumptown is breaking any records for a dry summer after all. But perhaps I'm wrong?

  2. Not upset, but a question: could this be due to changes in the Arctic oscillation from human-induced climate change?

  3. I also wish Dr. Mass would talk a bit more about us down here in the Willamette Valley as well. He did a good job last winter when the Oregon lowlands had several snowfalls and prolonged arctic events.

  4. Cliff, what to you would amount to evidence that any weather changes at all are related to global warming? I suspect that the answer is that you don't believe that anything at all would be conclusive but I'd love to hear from you.

    Show me your goal posts.

  5. Beginning to have doubts about SEA being the official Seattle reporting station (not the least of which is that it is not in Seattle) but having read past articles about questionable accuracy of their equipment, and its location smack in the middle of acres of concrete and the exhaust of hundreds of jet engines every day. Add to that the presence or absence of a single heavy rain shower compared to the city can make a complete difference in a record such as the one you discuss, especially this year.

    Not sure how accurate the downtown records are, but they cover a much longer period. Seems like between the NWS office at Sand Point and previous records from the Naval Air Station there, a history at least as long as SEA would exist? How about UW records?

    Yeah, I need a hobby...

    1. Good points, but they are still comparing the same location year over year.

  6. Hi Cliff,

    You stated: "As of noon today (Wednesday June 20th), Seattle-Tacoma Airport has received only .50 inches of rain. LESS THAN HALF of the previous summer record."

    Did you mean: "As of noon today (Wednesday September 20th), ..." ?

  7. Cliff, I'm a recent follower on your blog and still rather green in the area... so I'm curious: Have the number of records broken this year (for Seattle) been exceptional?

  8. John Bennett,
    Well, this is not a football game....but local evidence would include a coherent long-term (decades) of significant warming and loss of snowpack, or of such a trend in precipitation intensity. Such trends don't exist right now. ..cliff

  9. Along with Climate Deniers we have Climate Believers. I know their hearts are in the right place but again we need to make decisions based on facts and not belief systems - or we fall into the same traps as the Climate Deniers who claim that Science is just another Religion. I'm with you Cliff!

  10. It is important to remember that this record is for the Seattle Airport only -- it is a sample and subject to all we learned in statistics class about sampling error. As I was reading this post my rain gage in Kirkland read 1.56 inches for the previous 24 hours. That was after several days of one tenth inch (+/-) readings.

    In the Midwest it is not uncommon to have corn and soybeans killed by drought while less than a mile away the fields are green and lush.

    It has been a dry summer and lawns are brown. Is it the driest ever? For some, yes. For others, maybe.

  11. @ Jon Bennett - a long term pattern that is statistically distinct from the historical patterns (which will take a couple decades to verify). Alternatively, a lesser degree of indication this year's drought is climate related would be well-verified models indicating this sort of change should occur.

    Regarding the latter, research by University of Washington suggests climate change will not significantly affect precipitation volumes, although obviously, it would affect type: more rain, less snow.

  12. As for Stumptown precip. this summer, KPDX recorded just over an inch of rain on Wednesday and nearly 2 inches since Sunday. No record dry summer here, although only 0.21 inches were measured before this week's rains.

    Moving to the opposite extreme, on Wednesday during passage of hurricane Maria, a station in Puerto Rico saw 12.37 inches of rain fall in 44 minutes and 39.67 inches for the day. I wonder how long the validity of that will hold up. Absolutely incredible.

  13. As is the norm, the PWS near my house in Sequim shows less than half the rainfall of SeaTac. In my case, 0.24" from mid-June to today.

    I'm betting we'll be seeing a lot of damaged or dying trees over the next weeks or months, especially if significant rains don't return for a while. Sept and Oct can be the hardest months for trees if it stays dry. Soils are bone dry.

    If you love a tree, give it a good soaking now.

  14. Cliff, let me ask you, do you agree, in general, with conclusions from the latest IPCC assessment report?
    Do you think extreme weather events are increasing?
    Do you think there is any link of any of these events to climate change?

    Do you agree with this statement from the 5th assessment synthesis report?

    "Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse
    gases are the highest in history. Recent climate changes have had widespread impacts
    on human and natural systems."

    Do you agree that the planet is warming, if so, you just don't think this is having any impact apparently? How do you think it is impacting "human and natural systems" Every single major extreme weather event (Harvey, Irma, Alberta wildfires, etc,) it seems you always deny a connection to climate change.
    Do you believe wildfires are increasing due to climate change?

    If you don't why not , when all the data (and what would seem to be a majority of climatologists) say so?

    I think your approach is to separate out particular phenomena from the overall picture and not grasp any of the intereactions or links in climate. You continually miss the forest for the trees. I think you approach it as a metereologist but maybe don't really understand, or choose to investigate climatology And I believe you are just plain wrong.

    And in this , you do an extreme disservice to the community you are supposed to serve. Because they think you're an expert on this and they believe you. What it leads to is making the people who just don't want to believe climate change is too bad, that it's a problem for the future, so they don't have to do anything about it, just go back to sleep. And it's actually a tremendous present danger.

    Your positions I think are objectively at least, part of the 3% of scientists who don't really think clinate change is real. You seem to believe it's real, but just that it isn't really having any impact now and is a problem for the future. You're a climate contrarian-at least objectively And you also, in my opinion, approach weather events in the Northwest as disconnected from everything else.

    There are actual theories and some evidence for wavier jet stream occurring and impacting more presistent weather patterns in the mid-latitudes, particularly in certain season. This is linked possibly to artic amplification-warming of the arctic at a rate much higher than the mid-latitutes

    . People should check out this work from Jennifer Francis on this. Not proven yet, but very intriguing and worth pursuing.

  15. Maybe there is evidence of human contributions to recent heat records

    Mann, Michael E., et al. "Record temperature streak bears anthropogenic fingerprint." Geophysical Research Letters (2017).

  16. nice post carl!

    Blogger Cliff Mass said...
    John Bennett,
    Well, this is not a football game....but local evidence would include a coherent long-term (decades) of significant warming and loss of snowpack, or of such a trend in precipitation intensity. Such trends don't exist right now. ..cliff

    ^ does loss of nearly every "permanent snowfield" in the mountains count? or the fact that there is seldom a summer where there's still the preceding winter's snowpack sitting atop the glaciers?

    do you think loss of glaciers might have an impact to, oh i don't know, water supplies, electricity, fish, people?

  17. Hello all,
    Uh, I am not the sharpest arrow in the quiver, but if I am not being too blunt,
    Dr. Mass doesn't seem to respond to any of your questions or comments. Just sayin'
    I'd personally like to understand to what Dr. Mass attributes this record breaking
    driest summer. I mean we are talking about 70 or more years. I can't imagine
    that it's cyclical. Let's face it, we've really messed up the environment for
    certainly more than 70 years, and if anyone can prove otherwise, I'd sure like
    be enlightened.
    We in the Pac NW need to be more proactive--especially when it comes to lack of
    water (aka drought). Money should be used to be able to tap into the sound and
    even the coast (desalination) to provide alternate sources of water. Also, as
    the sun seems to be more in evidence, set up solar power, and certainly wind power
    in the Olympics and the Cascades. It's not rocket science, right? Just sayin.;-)
    Enjoy the blog, even without author responses.

  18. Oh great, here come the 'true believers' who worship at the alter of Bill Nye, Michael Mann, Al Gore and James Hansen. These guys are clowns, and only want your money and blind allegiance.
    To the true believer, everything is caused by AGW or climate change. It its wet, its climate change. If its dry, its climate change. If there's an earthquake or volcanic event, or if something seems out of place, (try putting your wallet and keys in the same place every night) or if there's any hurricane or typhoon anywhere its climate change. (Do some historical research like the 1938 hurricane, and you'll find that the resent hurricanes are not unprecedented.) Was the eleven year hurricane drought here in the SE US caused by AGW too? You can't have it both ways. This is a prime example as to why I've become a AGW skeptic in recent years. Want me to change my mind? Be consistent, stop the alarmism, and stop making this into a religion, and stop making this a political movement. Science and politics should not mix anymore than religion and politics should not mix. Oh, but its to late, you've already made AGW a religion.

  19. What is up with the PNA forecast for the Oct 7th timeframe?
    Does the mean with can expect another trough of low pressure?

  20. I'll bet I'm not the only one who misses the sun.

  21. What if climate change is all wrong and we create a cleaner, more sustainable, healthy environment for nothing? Whatever your position on global warming/climate change, why would you oppose clean air and water? While many of us wont' be around to see if the science was right about climate change, we could all immediately benefit from less pollution in the systems that are critical to our immediate survival. We are fully capable of doing this. We've come from living in caves to sending probes to Saturn, why we suddenly don't have the will to improve our situation is more concerning than anything.

  22. Carl,

    Cliff's not a "climate change denier" He always emphasizes that late this century it will change a lot more than it has. I do think he sometimes downplays the subtle changes we have seen so far such as retreating glaciers. My gut feeling is that we are seeing the beginning of climate change. But it is true that a year or even a few years of warmer or drier than average summers doesn't prove much. Cliff is just very cautious and avoids hype, likes to stick to hard numbers.

  23. I do think that the trees are suffering from drought even more than in 2015, and I am looking forward to the next "Pineapple Express. I hope it comes soon.

  24. Carl Barker - In my experience, Prof. Mass doesn't always RE-explain his scientific opinion in the comments section. After all, Prof. Mass has a life. He has however, answered all of your questions before in detail in previous blogs. I'm sorry that many of you dont like his answerers but his answers are all grounded in science and not hype.

    To Prof. Mass - My guess is all of these questions will go away soon. Maybe by 2022. I'm sorry that you may have to wait that long for all of these AGW believers to figure out that they have been misinformed and that the real driver of the earth's climate, the sun, has gone into it's grand minimum.

    Stay warm folks, Winter is coming.

  25. Weather Geek -

    You are a skeptic because you hear unskilled people hyperbolize weather events into sure fire signs of climate change?

    Thats a bit dumb isn't it? Try listening to what the skilled people say. That will knock the wind out of any skeptics sails.

    Well, ethical ones anyway.

  26. From NWS.

    Several people have gotten all excited about a dry summer. On the other hand it's been wet since last October 1 and since last January 1. Life goes on.

    156 AM PDT FRI SEP 22 2017


    YESTERDAY 0.02 0.94 1981 0.05 -0.03 0.00
    MONTH TO DATE 0.50 0.94 -0.44 1.02
    SINCE OCT 1 49.32 36.93 12.39 49.14
    SINCE JAN 1 28.92 21.53 7.39 24.75

  27. Weather Geek.
    Not believing climate change is happening isn't a religion-it's fact. Every weather event or even every extreme weather event is not due to global warming. Some are and some are not and climatologists are looking deeply into these events and trying to tease out what is what on this.

    Global warming/climate change though is contributing to a trend of increasing extreme weather events, which are yes, happening. You are a "skeptic". Do you believe the earth's average temperatures are rising? Do you believe arctic ice and Greenland are melting at accelerated rates? Do you believe sea level is rising? If you don't believe these things, you are just denying facts proven by careful study, repeatedly and over decades. So you're the one relying on religion and denial of reality.

    If you do believe these phenomena are happening, (and I've touched on only a few of the demonstrations of how the climate is changing), then what is your explanation? If you say, "oh climate always just changes", you haven't really looked at or at least absorbed how these trends are changing over time and are rising above natural variability statistically. If you think Michael Mann and James Hansen are doing this "for the money and blind allegiance", your head is not only in the sand-you're just buying right wing climate deniers bs which is only to keep going massive profitmaking by fossil fuel interests, and you're a poor judge of character to boot. You're the one relying on religion- blind denial of demonstrated reality. So save your outrage.

  28. To those trolls who are forever coming on to this blog to harangue and intimidate the proprietor into making far - reaching and conclusive statements pertaining to AGW and how it's going to kill all of us in a few years unless we DO SOMETHING NOW, I offer you the following news from the world of climatology:

    This kind of "oops, we were wrong again" has been going on for over two decades now, and yet believers in the cult will not listen to any objective analysis or reason to the contrary. They should just admit that they're only interested in controlling everyone else's behavior (other than their own, of course), and are in essence the very definition of "Science - Deniers."

    Either admit that you've been worshiping at a false God or go screech elsewhere.

  29. Eric Blair - Your phrasing of "screeching" and "worshiping" is to be conservative, a bit over the top so it is perhaps not surprising that you provide as evidence not the actual paper or even some peer review but The Australian and The Telegraph spin on it.

    Thus you perhaps were led astray by "Experts now say there is a two-in-three chance....." when they should have said these particular couple of experts say, not "the experts" in any sense of a global consensus. As you note, if you are going to triumphal pin your happiness on this, you may yet wind up disappointed as soon as next year. Who knows.... maybe even Cliff Mass will tear it to pieces.

    Nor was there any "condemnation" of the "over reaction" to Trumps pullout. I believe The Telegraph may have played you like a fiddle again, as they so often do.

    Either way you would also note this, if you instead read the authors press release:

    "Co-author Professor Michael Grubb of University College London, concludes: 'This paper shows that the Paris goals are within reach, but clarifies what the commitment to 'pursue efforts to limit the temperature increase to 1.5°C' really implies.

    'Starting with the global review due next year, countries have to get out of coal and strengthen their existing targets so as to keep open the window to the Paris goals. The sooner global emissions start to fall, the lower the risk not only of major climatic disruption, but also of the economic disruption that could otherwise arise from the need for subsequent reductions at historically unprecedented rates, should near-term action remain inadequate.'"

    Thats right - they are suggesting that we still need to do the work of transitioning away from fossil fuels and just possibly, we haven't blown it yet.

    Sorry to pop your bubble old sport. Better luck (you'll need it obviously) next time.

  30. Instead, they have pushed an ineffective agenda regarding global warming. And little has been done to discourage building at the urban/forest interface.

    Exactly what do you mean by this? Or would it by chance be some quarter-baked throwaway line, wholly unstudied, that you heard somewhere and decided to toss in there to curry favor with the usual academic suspects?

  31. "And little has been done to discourage building...:
    Higher fire insurance premiums on development so located? If not, why not?


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