Saturday, December 7, 2019

Why so Dry? Will it Continue?


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Announcement:  I will be teaching Atmospheric Sciences 101 during winter quarter

If anyone is interested, either a UW student or outside folks using the ACCESS program, I will be teaching this general introduction to weather in Kane Hall (210) at 12:30 PM.
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During the past week, there have been a number commenters asking the big W question.   Why have we been so dry?   Yes,  they understand that persistent high pressure (or ridging) over the Northwest and the northeast Pacific have been the proximate cause, but why is there such ridging?   And is it a random event or is there some underlying cause, such as global warming? 

Let's examine this issue here.


First, the proximate cause--the ridging or persistent high pressure.  Meteorologists often evaluate such ridging by looking a level in the mid-troposphere:  500 hPa--about 18,000 ft above the surface.

Below is a nice graphic produced by the NOAA Climate Prediction Center, showing heights at that level (analogous to pressure), with red/orange colors showing you anomalies (differences) from normal.  October and November is shown.   You can clearly see the wavelike nature of the flow aloft with alternating ridges and troughs (lower than normal heights).   A ridge sets up in the NE Pacific in late October and holds through November.     That is why we were dry, since ridges are associated with sinking motion and the lack of midlatitude cyclones and fronts.


During the past week, the ridge has shifted westward and an area of low pressure/heights has developed west of California.  This pattern has drenched California with the Northwest getting the meteorological "leftovers".   A bit of light rain, but not much of significance.  So far this month, Sea-Tac has only received .05 inches, over an inch below normal.


Now the first question many have is if there is a trend for such high pressure over the northeast Pacific.  If so, we would need to consider global warming as a contributor.   We can examine this issue easily by plotting the heights over a box encompassing the region for an extended period (see below)
Here are the results, plotting the 500 hPa heights over that box for November from 1948 to 2019.  Heights were record high in November, tying the extreme value observed in 1956.  But there is no clear evidence of a trend.  One way you can see this is by simply covering the last year in the plot.


Without a trend, there is little likelihood that there is a climate change origin to this feature.

So what is the cause?   First, it is possible that this persistent pattern is the result of chance, of the essentially chaotic nature of the atmosphere.  The atmosphere does not necessarily need a "cause" to produce persistent configurations.

But sometimes there is a physical origin of persistent patterns.  And one such mechanism deals with El Nino or La Nina.

El Nino is associated with persistent warm water anomalies in the central and eastern Pacific.   Such warm anomalies can shift the locations of thunderstorm areas in the tropical Pacific and in turn alter the upper level wave pattern in the Pacific.  La Nina is the opposite.

There are some interesting changes in the water temperatures and resulting thunderstorms/convection over the tropical Pacific.   But since this blog is getting long, my discussion of those anomalies will have to wait for a future blog.

But I will show you the prediction of the upper level pattern for the next week--the average 500 hPa heights and anomalies from normal over the north Pacific based on the European Center model.  Yellow/orange is above normal (ridging) and blue is below normal (troughing).  The ridging has moved back over us, which suggests below normal precipitation.   But substantial troughing is offshore--very reminiscent of a classic El Nino pattern.   But enough for now...




33 comments:

  1. At the risk of sounding opaque, does this mean possible El Nino patterns forming, or perhaps neutral conditions due to diametrically opposed conditions occurring in the same time period?

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  2. The national weather service in the extended forecast today stated we will start getting much more rain starting late next week.but Cliff is stating much drier conditions will persist.

    Which is the accurate forecast?

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    1. Accuweather has ~40% average rain chance here in SW Wa. We're usually on the drier end. Call me kooky, but it seems shorter term weather phenomena seem to be getting slightly harder to predict. I wonder if that is because there's no historical analog to model the rapid increase in CO2 and how it affects short term climate/weather events and El Niño and La Niña.

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    2. Short term weather forecasting is getting worse in the United States because our weather models are outdated and consistently under-perform compared to their foreign counterparts. Between that and a lack of funding, there has been a noticeable decrease in the accuracy and precision of forecasts issued by the NWS over the last 5-10 years.

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  3. Is it possible that warming global temperatures could result in "permanent el nino" effects in the PNW?

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    1. What do you think El Nino is? It's warming in the ocean. When the ocean is warmer then you get a 'permanent el nino" and becomes the new normal which then you will have even WARMER El Nino's spike.

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  4. The Blob is back, something Cliff forgot to mention. So even though this winter is supposed to be ENSO neutral, the Northwest is sitting in a stagnant warm pattern. Low precipitation amounts with high temperatures. If this isn't global warming and the BLOB isn't a symptom of it then why isn't the N.W. getting pounded by a parade of storms like the farmers almanac predicted? Because global warming is changing our weather patterns. This very well could be the new norm for Washington so if you like skiing it may be time to move to higher elevation states that benefit from higher elevation snow. Meanwhile Snoqualmie East is sitting at 2800' which will be well below the snowline indefinitely. Climate Change deniers I'd love to hear an explanation!

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    1. This comment has been removed by the author.

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    2. Yes, I was surprised there was no mention of The Blob

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    3. We are currently at the end of our 11 year solar cycle (24) one of the smallest ever recorded. going in to 25 which is due to start soon. There is some reading out there to support that years where sunspot production is very low leads to these very crazy weather patterns.

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    4. @Where is winter?

      First, I'm going to put more trust in someone like Cliff, who backs up what he publishes here. Second, I doubt he's hiding anything about "the Blob" as you seem to imply (a term which he coined, so I'm pretty sure he will track trends like that).

      Third, we ARE in ENSO neutral, any effects of which aren't typically felt until Winter, which we are not in yet.

      Fourth, the area of warmer water you're incorrectly calling the "blob" is moving further south of our area (or dissipating).

      You can see it here (notice also the area of cooler water developing off the coast): https://www.ospo.noaa.gov/data/sst/anomaly/2019/anomnight.12.5.2019.gif

      As for Snoqualmie East sitting below snowline "indefinitely," that is an alarmist bit of language which is almost nonsensical. The snow level was already below that THIS SEASON. Just because next week has snow levels above 3000, doesn't mean Winter will stay the same.

      Finally, almost no one is a climate change "denier" (which is another alarmist bit of name calling). Almost every person agrees the climate changes, and most can see the minor warming. But not RCP 8.5 apocalyptic climate change that you're basing your wild little diatribe on (which isn't likely to happen).

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    5. "Climate Deniers" is a deliberate conflation with
      The Holocaust. Anyone even attempting to make the analogy is only proving their utter lack of character.

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    6. Good comment Joseph. The above from "Where is Winter?" is ridiculous personal conjecture mixed with ad hominem.

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    7. No it isn't. It is you trying to link two completely unrelated events in an attempt to silence those who refer those who deny the science colloquially as 'Climate Deniers'. It is simply shorthand for a subgroup, who deny the very existence of AGW. A more apt term would be hard to come by.
      I have never ever thought of Climate Denier in the same context as denying the Holocaust. Personally, I believe you are soiling their memory making such a specious claim.

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  5. Is the warming of the Arctic and lack of sea ice in the Arctic partially to blame for the wobbly jet stream resulting in blocking patterns and "stuck" weather patterns?

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  7. Cliff, I've decided to just take the everyday weather as it comes. We really don't have any other choice. However, I do have empathy for those who want or need specific weather outcomes. Also, I enjoy knowing why the weather is behaving as it does. Thank you for sharing your knowledge with us!

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  8. I know you want to see trends to prove global warming, but all I ever see is trends of the same weather type predicted. So, if we see high pressure, we look for high pressure trends, etc.

    But have we compared the RATE of unique weather compared to previous years? We are seeing unique high pressure now, but are we also seeing a high number of other unique weather conditions (i.e. hot summers, historic low rain, etc, etc)?

    Why not look at all the types of record weather instead of comparing one to only itself?

    An example for clarity (numbers made up): Let's say in 2017 we saw 5 high temp records, 2 months with low rain records, and 1 month with high wind records. 8 extreme records broken. Then in 2018 we see 12 extreme records broken, then in 2019 we see 15 extreme records broken. Is anyone tracking this kind of stuff?

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    1. @Scott K. - Yes, Cliff and his department are. ;)

      What you mention in your hypothetical isn't enough to demonstrate a long-term trend in climate. (Typical statement is "weather isn't climate," but even that isn't entirely correct).

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  9. Cliff, I would like to know your opinion about snow next week. I saw the national weather service prediction, and for next saturday night, there will be moisture and near freezing temps.

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  10. cliff this is urgent please post. A 40 percent chance of snow after 10am. Patchy freezing fog before 11am. Cloudy, with a high near 33. Southwest wind 6 to 8 mph becoming east in the morning. New snow accumulation of 1 to 3 inches possible.
    Wednesday Night Snow. The snow could be heavy at times. Low around 30. Chance of precipitation is 100%. New snow accumulation of 9 to 13 inches possible.
    Thursday Snow. The snow could be heavy at times. High near 33. Chance of precipitation is 90%. New snow accumulation of 6 to 10 inches possible. this is for stevens pass starting season???

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  11. The snow storm that might be true?? There is an urgent discussion saying that stevens pass could get a huge dumping in 24 hours. Stevsn pass last snow storm called for 11” but they got 36 inches in 2013 but this time they call for around 23 inches my guess is 56 inches watch and see because this system will plow washington and get this season going. Posted:dec 7

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    1. Look at the revised forecast this morning, which suggests that with this storm pattern we'll get significantly less snow in the mountains than was predicted earlier. We'll see.

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  12. Even though our weather seems unpredictable, I can count on any question about the influence of climate change/warming in Cliff's posts to be answered with no.

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  13. I would so LOVE to take your class but I have to wait 10 years until I “age in” as an ACCESS student. Is there any other way to register for your course? I do have the means to pay for it.

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  14. I hiked up Mount Pilchuck yesterday- which sits in the convergence zone and should be under several feet of snow by now. Yet there was only about 4 inches on the summit.

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  15. Unrelated, but who can tell me why I experienced so much turbulence flying from Honolulu to Seattle last night between 5pm and about 8:30pm HNL time?

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  16. Unrelated, but who can tell me why I experienced so much turbulence btwn Honolulu and Seattle last night btwn 5pm-8:30pm HNL time?

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  17. I feel like this was half a blog. Looking forward to finishing the thought in the next installment!

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  18. Chilly, foggy day in NW Bellingham today. Max temp: 41.5F, min temp: 30.4F.

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  19. I would love to be able to take that class, but I am not a UW student and I am not over 60, is there any other way?

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  20. I have been doing ALOT of reading and I mean ALOT of reading on this matter. Because i've been terrified.

    I think it's not only the PDO that's causing our troubles. but the +AMO as well. The AMO and and the NAO are intertwined. I THINK the +AMO is the problem. When the PDO switched back to negative briefly our blocking problems did not decrease EXCEPT for those two double dip el nino years they pretty much remained the same.A persistent thorn in our sides.

    There are those who are going to disagree with this and say that the AMO does NOT have a strong enough correlation to effect us here.

    I would really like to hear cliff's thoughts on this matter. even though he says the atmosphere doesn't need causality to set up stubborn patterns such as this one.

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