November 13, 2009

Major Pineapple Express

5:30 PM update on Friday...its snowing in Everett...intense convergence zone convection plus cold temps aloft have brought thundersnow to the ground....

The numerical forecast models are consistently calling for a major pineapple expresss/atmospheric river event starting Sunday and extending through early Wednesday. These are amazing phenomena....I have an active project now studying them with a graduate student Michael Warner. Huge flux of moisture in what appears from satellite imagery (vertically integrated water vapor, above) as a narrow plume of moisture.

Check out the 24-h precipitation from the 12-km WRF run at the UW for the periods ending 4 PM on Monday and Tuesday (graphics). Vancouver Island and the Cascade/Coast Mountains on the mainland get hammered with a number of areas getting 5-10 inches and more. The Olympics and the northern Cascades also get large amounts..but less. The central Cascades receive far less (good for the Green River).

A major issue is that the freezing levels will move way up, with warm rain falling on some of the nice snow in the Cascades. Well, we can't escape Cascade concrete for long!


  1. on the 1st graphic, why is the plume on the bottom ( the one ppointed down) of concern to the Pac NW?

  2. It's "consolidating" and stabilizing all the new snow...

  3. MRB:
    Its not. Just an illustration that several atmospheric rivers can occur at one. That image is not for this situation..cliff

  4. I like that above map. Where would one find a precipitable water value map?

    I agree on the pineapple express is an interesting phenomena and needs to be reasearched.

    But I don't know when or where it started, but the Seattle media use that term too often and too loosely today to describe any event of it raining more than 2 hrs.

    With this storm, you can see how the upper flow is perpendicular, then diagonal, and finally parallel to the coastline. Wherever along the axis that line decides to rotate, it will rain hard for a long time. Let's hope its stays north. Express, definately, but maybe missing some pineapples.

  5. Here comes the November '09 flood!,1,1,1,1,1,1,1&toggles=10,7,8,2,9,15,6

  6. Cliff, can you please comment on the current Madden Julian event and its possible effects on our precipitation now and into the early winter? Can't find info anywhere. Thanks!!!!

  7. In the images it doesn't look like much of western washington will get hit by any of the jet stream of moisture. Am I just reading the images wrong or am I looking at the wrong images?

    It looks like it's all going north into BC.

  8. Can you cite some references (if any) in the literature to previous work on these "plumes" of moisture. Alternatively, can you post some .pdf files where this published literature can be accessed?


  9. 4:15pm Lake Stevens approx 300'

    We just had a Massive Hail storm hit us...actually it's still going. Dropped about pinball sized hail or larger and it's coming down HARD.

    Been going for a good 15 minutes. Looks like snow everywhere!

  10. Ok I saw it!...the first KIRO weather story that showed 5 pieces of slush on Snoqualmie Ridge, people buying snow shovels at Home Depot, etc. 5:05 pm November 13, 2009. The silly weather reporting season has begun!

  11. I think of a pineapple express as a series of warm, wet storms that hit our area. At this point, it doesn't look like that will occur. Instead, this will be a big, solitary event, followed by colder weather systems. For snow lovers (and folks who don't like floods) this resembles more of a coconut thrown at us (Ow!) not a pineapple express.


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

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