April 22, 2017

A Late April Precipitation Pattern I Have Never Seen Before

The model precipitation forecasts for the next few days is extraordinarily unusual for late April, with some aspects unique for any time of the year.

We are talking about an amazingly long and wide precipitation/moisture band coming from the west that will bring record amounts to some locations from northern CA to southern WA.

Let me show you what I mean and be prepared to be impressed.   I will start with the 24h precipitation ending 4 AM Monday from the UW WRF model (relatively coarse outer domain).  I have never seen anything like this:  a very wide band of precipitation stretching thousands of miles due east into the Pacific.  The width of the precipitation band is extremely unusual (very wide).

 Next, zooming in to the higher-resolution (12-km) domain for the 24h precipitation ending 5 PM Monday, one views a very wide precipitation band that is enhanced as it is forced to rise by the terrain in western Oregon and northern CA (1.28-2.56 inches indicated by the pink colors).  I have been looking at these model runs for decades and have never seen anything like it.

Or how about the cumulative precipitation through Tuesday at 5 PM from the vaunted European Center model?  The huge precipitation band is shown, with 2-3 inches from the Olympics to northern California.   Want dry conditions?  Head to the Columbia Basin.

To get an idea of how unusual this amount is, here is the % of normal for the above precipitation totals.  Some locations are 400% of normal.  But it is the north-south extend of the precipitation that really impresses me.

The moisture coming into the Northwest is from a zonal (east-west) atmospheric river.   During the winter, the most significant atmospheric rivers come from the southwest, but they tend to become more east-west during spring.  One measure of an atmospheric river is the vertically integrated water vapor graphic, that shows the total moisture in a vertical moisture in a vertical column of air.   The WRF forecast for 11 PM Sunday shows the high values (blue and reds) heading right towards the CA/OR border.
A forecast of atmospheric water vapor for 8 AM Monday shows the extraordinary east-west extend of the the water vapor plume, which originates over the southwest North Pacific.

You can see the ejection of the moisture from the tropics into the midlatitudes in this animation, which show the distribution of water vapor during the past few days (click on image if it doesn't animate).  So the substantial rainfall we will be experiencing can be traced back, in part, from moisture starting over the Philippines.

The depressing fact:  here in the Pacific Northwest we are living through a record-breaking wet winter and spring, and the action is not over yet.   The good news:  we should transition to an El Nino next winter, which should be associated with a different, and drier, atmospheric circulation.


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  1. So, basically, I couldn't have picked a worse year to become a market gardener then? Pardon me while I hook my sump pump to drain my fields again.

    1. I am certainly missing the 6 days of heat records we posted last April.

  2. Cliff, any threat to the Oroville Spillway? Storms look to a bit north of any major impact, but this much warm rain combined with the unusual snowpack might spell problems down there.

  3. Are you sure you feel that confident about the El Nino probability at 52% by ASO? The thermocline slope is still positive or very close to zero. Temperatures in Nino 3.4, 3, and 1+2 have actually declined over the past few weeks, and there is a strong surge of colder water coming up along the South American coastline. I feel more confident that you are not using all of the available data to support your ENSO claim. And, if take into account the approaching solar minimum, your chances of any significant solar influence towards strengthening an El Nino are further diminished. Bonus gardening tip - I highly suggest that you just go and buy vegetable plant starts from the stores now rather than trying to grow plants from seed indoors for transplant. You are already at least two months late for that idea to reap any real benefit for our specific grow zone.

  4. Dr. Mass, do you see any hope for decent weather the week of 4/30 - 5/6? We booked a trip to Vancouver Island and the San Juans at that time, since early May generally has some gorgeous spring weather. With this being the winter that never ends, I'm starting to fret that we'll be washed out.

    Showers are ok as long as we have sunbreaks from time to time. What do you think?


  5. Even though this gloom and doom has over extended its welcome, I find it fascinating to hear your enthusiasm about how unusual it is, and that makes this "spring" weather fun! We've had a very interesting fall, winter and now spring to say the least. I predicted an average hi for the month of 4.4 degrees below average, and precip. as measured at the Portland weather office of 3.86". We'll see how that works out, I may have UNDER estimated the rainfall.

  6. How long will it be until someone blames it on anthropogenic global warming?

    Too hot? AGW
    Too cold? AGW
    Average? AGW
    Too wet? AGW
    Too dry? AGW
    Average? AGW

    1. Actually the large wave pattern of the jet stream is believed to be associated with global warming and shrinking polar ice, it tends to become stuck in a pattern that, depending on what part a region is in, can be either much wetter or drier than average.

  7. I find it hard to believe that this winter and spring's absurdly long and drawn-out (and might I add, long past the 'unwelcome' stage) period of wet and gloomy weather isn't due to climate change.

    I'm long past the argument that it's not, and I'm growing ever more impatient with the people who think climate change isn't causing it.

    I'd like them (Cliff Mass included) to explain to every astronomy club in the PNW that has had to cancel planned star parties and astronomy club gatherings because of incessant, drawn out periods of rain that are frankly unprecedented and never before seen in this part of the world.

    Ten years ago, I averaged 25 clear nights at the telescope from October to April. This year alone I've only managed four clear nights. It has been getting progressively worse over the last four years, and astronomers are growing tired of the 'It's not climate change!' argument. And we're growing really sick of all this constant rain and cloud cover.

  8. Is it confirmed this is the wettest Oct-April on record? Unbelievably constant rain and clouds this year, it has everyone I know going a bit crazy, or depressed.

  9. Y'all need to change hobbies. Every NW skier I know is LOVING this winter including its tenacity.

  10. My ducks and geese like it, but the chickens blame me. My dog is ready for a divorce. If we have a couple more winters like this I'm moving.

  11. The last El NiƱo coincided with a record-breaking WET winter (2015/16 water year). I hope if we get another one next winter, it's of the dry(ish) variety!

  12. Brian,

    Believe it or not some of us skiers actually ski better if we get enough sun to see the slope profile. Especially us back-country types. And with the sun out, you don't freeze when you stop for a picnic.

  13. Oh for God's sake, is there ANY weather that the cult won't hold out as "proof" of man-made global warming? Do any of you realize just how much all of your pronouncements kill your credibility?


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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