Monday, December 2, 2019

The Driest November in 43 Years

November was an extraordinarily dry and sunny month over Washington State.

In Seattle, the monthly total was only 1.71 inches, 4.86 inches less than the normal 6.57 inches (26% of normal).    More like our typical rainfall in September or May.


Spokane received .68 inches, only 30% of the normal 2.30 inches.

How unusual is this?   The last time Seattle was drier  in Novmeber was in the extraordinary winter of 1976, 43 years ago.

For Spokane, you would have to go back to 1993 to tie this November and 1976 to beat it.

Yes, 1976 was a startlingly dry year with a ridge of high pressure dominating much of the winter.

To get a spatial perspective on November precipitation, here is the difference from normal for the month.  Western Washington and Oregon were quite dry, with precipitation amounts that were 4 to 16 inches below normal.

But if you want to be impressed, here is the percentage of normal for the month.  Much of the Northwest received less than 25% of normal precipitation in November.


What makes this dryness particularly notable is that this should be the wettest period of the year.

The origin of the dry conditions? 

High pressure over the northeast Pacific.  To see this, here is the different from normal (the anomaly) of 500 hPa (about 18,000 ft) heights.  Substantially HIGHER than normal heights over the northeast Pacific.  Equivalently, think of unusually high pressure to the northeast  of Washington.  Such high pressure results in a much drier than normal conditions over the Northwest.  Cooler as well.

What about the future?

Amazingly, more of the same.  Take a look at the latest European Center precipitation prediction for the next 10 days (the anomaly, or difference from normal, is shown).  Dry over the Northwest and very wet over central California, the result of the jet stream heading south into the Bay Area.


Is the new normal expected under global warming?   Probably not.  In fact, our climate models suggest the opposite:  warmer and wetter conditions in November for our region as the planet warms.

39 comments:

  1. Hi Cliff,

    Can you speak to the cause of the persistent ridge? Would you attribute it to the positive SST anomaly over the North Pacific or is the causal relationship reversed?

    Thanks!

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    1. Would like to see this question answered. Seems like persistent ridges have become the usual suspect behind Northwest weather anomalies but would be more helpful to have some explanation behind what is causing the ridges themselves. A post on what is considered "normal" Northwest ridging patterns and their "normal" frequency of occurrence would be great.

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    2. Ive been doing some reading on this and i think it has to do with the decline in solar activity. Solar cycles 21-24 have been slowly declining in activity.

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    3. I second that! I've been wondering the same thing.

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    4. Great question! Another observation; the models seems to struggle with the eventual breakdown of the ridge. Might be a few days, weeks, or months.

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  2. As a whole, 2019 has been this way for western Washington, particularly the coastal region and the northern tier of the state:

    https://hprcc.unl.edu/products/maps/acis/subrgn/WA/YearPNormWA.png

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  3. Port Orchard got 2.11 inches of rain in November. I've been keeping a November rainfall chart for the past 11 years and we've gotten on average of just over 9 inches for that month. The most was over 15 inches in both 2009 and 2012. So this was an incredibly dry month.

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  4. You state the next 10 days as dry over the PNW though the NOAA 6-10 and 8-14 day forecast suggest wetter than normal conditions?

    https://www.cpc.ncep.noaa.gov/products/predictions/610day/
    https://www.cpc.ncep.noaa.gov/products/predictions/814day/

    Any comments on the discrepancy? Though the euro model shows a split with more precip both north and south

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  5. hey cliff not sure what this winter means do we get no snow but really cold like 2015-2016 i cant remember what year but anyway do we get snow or no or will it be like last winter when we got a lot of snow at the end of winter like feb.

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  6. Climate Prediction center: 8 to 14 Day Outlooks Forecast 80% Above Normal Precipitation.(Valid: December 10 to 16, 2019
    Updated: 02 Dec 2019)

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  7. The 2018-2019 water year yielded 25.38" of precip at my location in NW Bellingham. The average annual precip at BLI is 35.83", though my location seems a bit drier as the max water-year precip that I've measured is 31.83". The 2018-2019 water-year precip total at KBLI is 31.39" - about 88% of normal.

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  8. Are there any hypotheses about climate change and the greater AO oscillations, or perhaps an eastward shift in the AO?

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  9. It would help interpretation to see error bands or at least basic variability (low, high, standard deviations etc) as well as 'average' (mean?) metrics, for as long as WA data are reliable.

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  10. Every now and than we get a year like this. 2000-2001 was also a very dry Fall/Winter. It could still change. We had a wet September and before that a normal summer. We have had dry periods turn into wet periods and vice versa. Look at 2009 one of the wettest November's was followed by a dry December and one of the driest February's on record in 2003 was followed by a wet and stormy March.

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    1. Exactly, yes - I don't remember many years (ever) being the same-same-same. And yet, many expect that kinda "normal," and point at statistical averages as-if there's some implied guarantee of x, y, or z.

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    2. Amazing...this is the 43rd weird year in a row!

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    3. Global: If variable seems "weird," so be it. There's a very (very) wide range of everything, both seasons and degree. Spring isn't "due" on March 1. Winter doesn't set-in on schedule, either. Some years we may not have much of a winter at all. In the many years I've lived here, more often than not people have wondered "whether or not there will be snow for Christmas." We're ten miles as the crow flies from the peak of Mt. Baker and there some years I didn't have my snow shovel out more than a couple of times and the ski area had a nice base; other years we had snow stacked up to the windowsills yet no records were set on-high. Normal = weird; yes.

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    4. Which was the point I was making, albeit sarcastically.

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  11. What's really interesting is how WET the 50-60 days were just before that spell, at least in the Whatcom headwaters. I documented .20" per day average.. visualize a full inch every five days during months that are typically "the seasonal summer dry period."

    A very early fall season followed, all those gorgeous colors. But that was accompanied by early frost and Nina fide cold weather setting in way ahead of what's typical - dare I say normal. It's as if the whole calendar slid...

    Now, what I've observed over a very long time is that there's a very wide range of normal. Big variations (calendar-wise) do not surprise me as such. Whatever the timing, it's far from "dry" here, and that's a fact. As for instream flows, most high tributaries have begun freezing. Four of the last five nights here were in the teens. Streamflow stats mislead when cause isn't understood Tealeaf reading - numbers alone - not enough without context. I'm very interested in knowing whats happening west of us, in the Pacific.

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    1. Yes. We did get robbed of our fall. Straight into winter. But all this seems within our 'normal' window though. But I'm not a scientist. Just an old guy that's lived in W WA his whole life. And I'm tired of this cold, gray weather.

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  12. I remember that winter of 76-77. My buddies and I climbed mt. Washington in the SE Olympic mountains in February expecting the usual deep snow and icy conditions. It was dry and mild all the way up to the last gully, which had just a short stretch of deep soft snow over the previous seasons ice in the shadier portion. I recall seeing a billy mountain goat giving us the evil eye, looking miserably warm in it’s full winter coat. It was a few years later that El Niño and La Niña became part of the public awareness.

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  13. I don't understand why there is the general assumption that global warming would lead to drier weather. Warmer air can absorb more moisture, which then brings more precipitation in the mountains. I wonder whether this would paradoxically lead to glaciers thickening at higher elevations. Also, if more moisture is absorbed by the atmosphere, this should at least in part compensate the sea level rise due to the claimed melting of the glaciers.

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    1. A warmer atmosphere will absorb more water vapor so most places on earth will get wetter but a few spots may get drier. There is more evaporation when its warm, in some spots evaporation will increase more than precipitation and even though its a little wetter it will feel drier. There are a few very high altitude glaciers that are thickening due to increased snowfall but most glaciers are at a lower warmer altitude and are melting. If the earth continues to warm even these very high altitude glaciers wills start to melt. The Taku glacier near Juneau alaska was growing until a few years ago now it is starting to shrink.

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    2. Is there any evidence for the models for Pacific NW? Have the falls and winters been any rainier in the last 10-20 years? Has there been a trend correlated to temperature increases?

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  14. Cliff, Thanks for letting us know what is expected with global warming in the future--warmer and wetter during November each year. Knowing facts expected make it seem more manageable as we make plans for addressing climate changes. It seems to potentially reduce peoples' overall fear and anxiety. Also, knowing what ways we need to adapt makes it seem realistic to develop strategies with technology, etc.

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  15. It seems like we had a wetter than normal October, too. Like they switched.

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  16. http://nwafiles.nwas.org/digest/papers/1977/Vol02No4/1977v002no04-Wagner.pdf

    That winter was considered extraordinarily harsh everywhere else, even if it was a non-event in Washington. The persistent high pressure ridge is not a new invention and we probably have not seen its full fury yet. It is highly possible we just don't get a winter this year here but everywhere else gets clobbered. The following year things did a 180, but 1977 was known for being a drought year in the West. Perhaps there is data from that era that corroborates with what we have been seeing here so far this season.

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    1. The winter of 1976/1977 was one of the warmest and driest on record in the western United States. Winter 77/78 brought above average snowfall to the great majority of the western US.

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  17. don't get me wrong, we do have those neutral winters guys this might be this time of the year or it could be a trick. Look at the weather for Williams lake BC that's are weathermaker right in that area I hope the warm weather turns to cold fast we need at least 1 good snowfall!! and Cliff you should add likes, so you can like other comments.

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  18. So, the rain missed us and hit No. California. They will be glad. And I'm glad too! Win Win!

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  19. It is important to recall the three, two and one month long range forecasts from the "state of art" weather models such as the NMME, IMME and CFSv2. Every model was for Above Average Rainfall for all of WA and Or. This begs the question (and I know you have heard it before), why believe any forecast for the next 10, 20 and 30 years if they can't get the next few months correct? The driest Nov in 43 years is a major BUST!

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    1. The short answer: Models used for shorter-term forecasts are entirely different than longer term ones. There are more expert voices than me on this, but to use an auto analogy it would be like you criticizing Uber for an occasional ride and equating that with driving your regular car around.

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  20. Today was the first day to reach 50F since 11/24 at my location in NW Bellingham. Shallow, standing water in North Whatcom County is still in the process of thawing.

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  21. Cliff, my only worry is that this droopy winter is bad so far we are near 50 degrees and its december, do you think at anytime we will eventually get cold i need a comment on this please anyone?? im only 14

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  22. Cliff, look at how much more visually effective the European Center precipitation prediction graphic is than the NOAA climate graphics. NOAA and similar agencies cling to this rainbow gradient which does a very poor job of showing high/low contrast. Does this every come up at conferences? Do the agencies that develop these graphics employ any cartographers or graphic designers? It sure doesn't seem like it.

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  23. we always get 50 degree days in December. Relax. there were just several days with lows in mid 20s across most of the region. It will get cold again, chill. stop mass hysteria.

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  24. Just curiosity. Has anyone plotted the global temperatures of the last 150 years against the atmospheric CO2 content for the same period and calculated the Pearson's linear correlation coefficient? Not trying to prove or disprove anything. I just would like to know what R is.

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  25. Hi (I think there must be several of you that go by "Unknown") Anyway, each year is different and no, I don't think this is all that unusual, though I agree it is time for the rain and (in the mountains at least) snow. Our average high in December is about 46 degrees, so this really is not that unusual. Consider our recent cold snap- it is the precipitation that we are missing. Personally, I'd like to see a Pineapple Express. Our temperature fluctuations are, in general, less than those of most of the rest of the country. Odds are, although there are exceptions, we will have our usual rainstorms in the next few weeks. I have noticed that when early winter is deficient in some way, it often makes up for it later. Same is true in summer.

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  26. http://kpudhydrodata.kpud.org/Rain_Yearly/01_YearlyRain_2020.pdf

    Gee, thanks rain shadow. Sequim is that way *points to the Northwest*. Think this is year 2 of weather mostly tracking straight from West to East. Nothing like being robbed of what little rain does fall while being in the donut hole.

    To the poster above: It was plenty cold last week. Now its time for more 50 degrees and ZZZZZzzzzZZZ. Nap time!

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