Sunday, March 31, 2019

Rain Returns to a Dry Pacific Northwest

We have just experienced an extraordinarily dry second half of March, one in which weather systems and their accompanying precipitation was directed southward into California.

Well, all good things have to come to an end, and for us the spigot will be turned back on this week.

But first, let me impress you.  Here is the percent of normal precipitation for the past two weeks over Washington State.  The dark red is less than 25% of normal!    No wonder some some media outlets are throwing around the D word (drought!) or predicting a dry spring.


But percent of normal precipitation can be very deceptive, particularly in places or times that are relatively dry (like our summers or east of the Cascade crest).  Far better is to view the departure of precipitation from normal (in inches) as shown below.  Dry eastern Washington was generally less than an inch below normal.   The Puget Sound lowlands, 1-2 inches down.  More over the usually wet western slopes of the Cascades and Olympics.

But everything changes this week as the large-scale atmospheric configuration changes profoundly.  

For nearly two weeks,  there has a deep low over the eastern Pacific, with the jet stream and accompanying storms heading into California.  This is illustrated below by a weather map for 11 AM Wednesday for an upper tropospheric  level (300 hPa pressure level, about 30,000 ft).   Yellow colors indicate the strongest (jet stream) winds. Washington State gets little precipitation from such a pattern.  


But the pattern greatly changes this week, as low pressure retreats into the Gulf of Alaska (the normal position) and the jet stream moves northward right into us (see the forecast map for 8 AM next Sunday)  We get nailed and California finally dries out.


Let me show you the precipitation forecasts from the UW WRF modeling system.  Here in Seattle we have two more days of dry conditions, but Oregon gets hit earlier.   The total accumulated precipitation through 5 PM Tuesday (shown below) predicts that western Oregon will be very wet during the next two days.


One day later (5 PM Wednesday), it is clear that the hose has reached western WA, with the Olympics and north Cascades receiving several inches.


But why stop there?  Here is the accumulated precipitation through 5 PM Sunday.  Wow.  The Olympics and mountains of southwest BC get 5-10 inches, with the rest of western WA and Oregon enjoying 1-5 inches.


We had a cold/snowy February, a dry March,  and now a wet April?  We will see.

But one thing is sure....  you can not believe the long-term forecasts.  Here are the extended predictions of the NOAA/NWS CFSv2 seasonal forecast model run in late February for the precipitation anomalies (difference from normal) for the end of March.   The CFS was going for WETTER than normal conditions over our region for the period....when it was very, very dry.  And dry or normal in California, where it was very wet.

No skill.   


25 comments:

  1. Cliff,

    You have always said the level of skills drops dramatically even after a relatively short time.

    At first, I simply accepted it. However, as I've followed your blog I am starting to gain an appreciation for the atmosphere's operation. There is a real beauty in the atmosphere's many combinations of factors affecting the weather. It makes sense why you chose your career--it must be fascinating.

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  2. Or you could run a map of the whole water year since that is the key statistic in all of this, and that would show a healthy year for water not just here, but up and down the west coast. For Seattle, SPU has spent the better part of 4 weeks dumping water out of our reservoirs to make way for the snowmelt.

    Speaking of dumping water... looking more and more like the new Oroville dam spillway will be used this year, quite possibly after this next system hits N. Cal. Should I go back and find all of the predictions in the last few years that claimed CA was in a permanent drought? Because that kind of fear-mongering speculation is way more damaging to science and credibility than these long term forecast misses.

    Thanks for the great blog Cliff.

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    1. I agree with your comment. Overall water year is solid. There's no drought because the snowpack has barely even started to melt. The rain fall we get from now until the usually very dry months of July and August will be the deciding factor if we get a true drought or not but with the snowpack being decent I cannot see much of a water problem unless we have very dry conditions lasting months eventually causing water shortages but not until late summer. So in other words way too early to even mention it and it would have to be like a repeat of spring 2015 to set us up for summer drought.

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  3. Was the wetter prediction due to the near term/recent snow events, so they were building off that to predict more near-term wet weather?

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  4. Cliff, any idea why the area south of YKM airport shows so much precipitation? That dark blue circle on the map is reminiscent of the temperature issue they had with the airport sensor awhile back.

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  5. Bring it on. I think our forests and parks need a good drink before summer gets here.

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  6. 12zGFS has the heaviest rain going north of Vancouver B.C. now. What gives! In fact it has the central and north coast of BC getting walloped for basically 2 weeks in what is usually a rather dry month for that region. They need the rain too though. But CPC still looking green for the 6-10 and 8-14 day for our region.

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  7. sunsnow12:

    By your definition, what criteria must be fulfilled for the water year to be considered healthy. Here in NW Bellingham, I've measured 15.05" since 10/1/18 compared to a normal value of 24.61" for the same period. At 61% of normal, healthy would probably not be the first descriptor that came to my mind.

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  8. Interesting points Cliff.

    I personally have been frustrated with the lack of "skill" in seasonal forecasts.

    But what strikes me is your first point on precipitation. How easily the same data can come across two ways.
    (Deviation from % average precipitation verses percent average in inches.)

    Same data two different impressions!

    It is critical for lay people to understand the nuance!

    It is my opinion this is the Crux of the climate change consensus roadblock.

    Anyway,
    At my location on the Quimper Penninsula, it is bone dry and has been bone dry since the first of the year at least.

    Seasonal ponds and lakes look like July levels. Yep.. that means it's dry. Nothing quite like good old observation and awareness of your surroundings.....

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  9. But with all this spring rain the weeds will grow and give us wildfire problems in the summer.
    As far as the Columbia basin goes the soil is very wet right now and no irrigation has begun. Moses Lake water temperature is 41

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  10. @jeff But just north of the area you refer to as the Columbia basin it is dry, soils are dry and we got less snow than we normally do. Bring on the rain.

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  11. Today is a good day to download the western Snotel snowpack map. April 1 is the standard reference date for the SWE.

    https://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/west_swepctnormal_update.pdf

    As you can see, Washington, particularly the Olympics and Northern Cascades are not in great shape, averaging around 70% of normal. The Southern Oregon Cascades and Eastern Oregon are better, being somewhat above normal, but that does not mean much for Washington.

    Another good source of regular information is the monthly newsletter form the Office of the Washington State Climatologist. The April newsletter will be available in about 10 days. The Snotel maps are included as well as drought discussion. Unfortunately, we are already experiencing early drought issues in Washington.

    http://www.climate.washington.edu/newsletter/

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  12. Jonathon Doe - so you're using your own personal water measurement, instead of the official estimates? That appears to be highly subjective, don't you think?

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  13. Jonathan Doe - My definition of a healthy water supply is a combination of reservoir height and snowpack so that by July 1 (when the vast majority of snow has melted in our watersheds) reservoirs hold enough water to comfortably make it through our NW summers (ie dry).

    There are always specific areas in large geographic regions that may have significant variances (wet/dry), but since Bellingham water is supplied by Cascade runoff I would be more than confident this year. The water managers in our region are also very good at what they do... see 2015 when we had virtually zero snowpack followed by a dry summer and still had significant water in storage (20 billion gallons for Seattle left over on October 1). It is why we have reservoirs and pros to manage them.

    Pine - the Columbia Basin is currently (today) at 84-88% snowpack -- even after this March dry spell. Statistically that is not "dry".

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  14. Morning low in NW Bellingham 34F, afternoon high 69F.

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  15. sunsnow12:

    Your optimism seems somewhat misplaced given your stated definition. See MAC's post regarding Cascade snowpack.

    Also, Lake Whatcom is not exactly a typical reservoir for this region given that it's tributary streams originate in low elevation areas which typically do not receive substantial snow. The only reason the Lake is able to function as the primary drinking water supply for Bellingham is due to the diversion dam on the Middle Fork Nooksack. Given the already low snowpack in the region combined with the likelihood of continued drier and warmer than average conditions, our saving grace will be, as you mentioned, the skill and experience of our water managers.

    If only water availability was the only issue of concern for poor Lake Whatcom. Alas, the heavily developed nature of the watershed combined with continuing warmer and drier conditions will inevitably lead to increased irrigation and fertilizer application which causes harmful algal blooms along with increasing hypoxic/anoxic conditions in the lake placing excessive strain on filters as well as the capacity of the treatment plant to ensure a suitable supply of clean water for drinking and sanitation.

    In short, I stand by my original contention that "healthy" is not the adjective I would choose to describe our water situation at this time. "Adequate", "so-so", "cromulent" perhaps; certainly not catastrophic but potentially a cause for concern. "Healthy" would seem to indicate robust and without cause for apprehension which just seems to me to be a perspective viewed through rose-colored lenses.

    2 of the past 14 months in Bellingham have featured above average precipitation with all others below average - sometimes historically so. Is that healthy?

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  16. Eric,

    I don't understand your comment. How are empirical measurements constituting hard data of good quality highly subjective compared to official estimates? Are you taking issue with the accuracy or calibration of my instrumentation? Is your sarcasm lost in hyperspatial translation or am I having a dunce moment? Please elaborate.

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  17. On the news last night they presented a map of the U.S. showing the NW as among the highest risk places for wildfire this year. I really hope they're wrong because we've had enough of that.

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  18. No sarcasm intended, just an observation about measurements originating from a hyper - local perspective. Things are not always as they appear.

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  19. Jonathan - can you please provide us a link to the Lake Whatcom reservoir height as it stands today?

    I would be absolutely shocked if it was not at a level that will have it maxed out when the Mt. Baker snowpack is delivered in the next 2 months. There has been plenty of precip (rain) this winter to fill our reservoirs, in fact the majority in the western part of the state were probably close after the fall. Seattle was as much as done in December, it was only a matter of adjusting for snowpack, which is why they have dumped water multiple times in the period.

    "Robust" is exactly a word I would use for full reservoirs in June... in any year. That's the way it works in our state. "Snowpack" does not feed reservoirs in July, August, or September except at the very highest of elevations.

    And yes, I am an optimistic person. That's why I am happy to say the new Oroville dam spillway is officially in use and working great! https://www.abc10.com/video/news/local/oroville-dam/watch-oroville-dam-spillway-opened-for-first-time-in-two-years/103-a3ed81d5-96eb-4fe3-b5de-1ab5643cbf09

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  20. Cliff, in previous blogs you have explained how many runs are made using the forecast models to get a "consensus" forecast. The magazine Science in the February 22nd issue had an article that reported on a study done by Fuqing Zhang at Penn State. The conclusion of the study was that forecasts are not reliable for two weeks out. This is due to small differences in the initial conditions input to begin the forecast. This is the effect known as the "butterfly effect". I believe this is due to the models using non-linear equations that magnify the differences in outcomes as time goes on. So this raises some questions. What determines the range of differences in the initial conditions? Do the differences in initial conditions depend on the how stable the current weather is, e.g. a large high pressure system over the area as in summer or rapidly varying conditions as during winter storms? What determines the uncertainty in forecasts, is due to the variation in the model runs which is determined by the degree of variation in the initial conditions?
    Maybe you could elaborate on this sometime in a way that us lay people can understand.

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  21. Sunsnow

    The term drought is surprisingly complicated. You’re talking about hydrological drought. Reservoirs, lakes, stuff like that. Not usually a problem here in the PNW. Johnathan Doe’s comments are more about meteorological drought (a lack of normal rainfall). Farmers worry about agricultural drought. Dry fields require more irrigation.

    https://en.m.wikipedia.org/wiki/Drought

    ********

    My main concern is with forests and forest fires:

    “and Drought, especially prolonged or severe drought, can be a major stress in forest ecosystems. Drought can kill trees directly or indirectly through insect attack or wildfire. Both of which are more likely to occur during drought.

    Tree mortality impacts most of the ecosystem services provided by forests, including the amount of wood that grows, how much carbon is captured and stored, the health of critical wildlife habitat, water yield and quality, and even whether it’s safe to pursue recreational activities such as hiking or hunting.”

    https://www.fs.fed.us/blogs/managing-forests-face-drought-%E2%80%93-there-help

    The last two summers my backpacking plans were severely messed up by smoke. In past years if it was smokey in Oregon I’d just head to Washington or California, maybe east to Idaho. No escape in 2017 or 2018. I’m hoping this summer will get back to normal.

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  22. My measurements are indeed taken from a single sampling point, however, the fact that surrounding stations employing high-quality instruments where precipitation is measured comport well with the anomaly that I have observed (I make a habit of keep track of such things to ensure that I'm not experiencing calibration errors) would indicate that my measurements likely constitute a representative sample. For things to be not always as they seem, my sampling point would have to be either very poorly situated (it is not) or would need to be located within a microclimatic region which not only is subject to anomalous measured precipitation values but anomalous anomalies of precipitation and the law of parsimony along with just plain common sense makes this extremely unlikely. That is unless your definition of hyper-local is squishy enough to mean anything from a single backyard PWS all the way up to an entire WRIA.

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  23. Snape,

    Thanks for clarifying my position. Long-term meteorological drought is precisely my concern as the effect of short-term hydrological drought is much easier to manage. It's considerably more difficult to conjure precipitation than it is to move stored water around as needed. As you indicate, full reservoirs are small comfort when you're choking on air that the residents of Beijing would find appalling. I, too, am an avid outdoorsperson and the smoke indeed hampered my typical summertime backcountry adventures.

    Of course the connection between hydrological and meteorological drought should be obvious as well in that reservoirs cannot simply stay full if not enough water is coming from the sky to keep them that way. As well trained as our water managers are, eventually a day of reckoning will approach when meteorological drought can no longer be considered in isolation from hydrological drought...that is unless we (hopefully) begin to see precipitation amounts much closer to normal than have occurred in the relatively recent past.

    Western Whatcom County's average precipitation distribution is such that it's climate is traditionally classified as Marine West Coast or Oceanic while the greater Puget Sound region is considered to have a Warm Summer-type Mediterranean climate. However, during the past several years, summers have been so dry in NW Washington that we are seeing a more Mediterranean precipitation regime with summertime rainfall anomalies even more profoundly negative than those occurring to our south.

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  24. MAC in Bellingham said...

    "Another good source of regular information is the monthly newsletter form the Office of the Washington State Climatologist. The April newsletter will be available in about 10 days. The Snotel maps are included as well as drought discussion. Unfortunately, we are already experiencing early drought issues in Washington."

    The April OWSC newsletter is now avaiable. I find it interesting reading.

    http://www.climate.washington.edu/newsletter/2019Apr.pdf

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