Pineapple Expresses affect our region several times a winter. Whether they overwhelm the benefits of the Olympic Rain Shadow is a very interesting question. I’ve seen it go either way, and my thoughts on climate when I put the site together leaned toward an answer of yes. But data from a recent storm suggests perhaps otherwise. Some background below, and a bit of analysis.
As I see it there are three broad categories of winter storms that impact the areas within the Olympic rain shadow…
Arctic Express - A great example of this was the recent mini-blizzard that hit Monday before Thanksgiving, 2010. Storm track from the NW, Cold Frazier River outflow, reverse rain shadow, snow in the Shadow, a lot of snow!
Zonal - What we back country skiers love; storms with defined cold fonts arriving from the west; sometimes stacked up, looking like “commas” on the satellite imagery.
Pineapple Express – “plume of moisture” originating from near the Hawaiian islands.
Well just today there is a very well advertised Pineapple Express bearing down on our areas Sunday. See Scott Sistek blog post from Komo, or Cliff Mass’ post today.
Will Pineapple consume the Shadow, resulting in gloomy, wet, depressing weather everywhere? You’d think it might, but my data suggests the Shadow might prevail!
For some perspective, I looked back at the last such storm, which hit from 4 am to 4 am on November 1st, reducing our gorgeous snow pack at Hurricane ridge from 20+ inches to near zero. Cliff Mass blogged extensively about this storm. I worried about it! Luckily it move through a bit quicker than originally anticipated and we didn’t get major flooding.
During the Nov 1 Pineapple Express, the Shadow Prevailed
During the Nov 1 Pineapple Express, my Sequim weather station near the center of the shadow recorded only .26 inches of rain to Seattle’s 1.16; we recorded 2.34 times the solar radiation, with 4 hours of dark skies, 2.5 of gray skies, 2.5 of bright skies, and zero hours of clear skies, qualifying for what I would would call a bright overcast day.
During the same period, Seattle’s UW station recorded 7.5 hours of dark skies, and only 1 hour of gray skies, resulting in a clearly dreary day.
Here is the radiation graph that day.
Well, it wasn’t a great day in the Rain Shadow, but it clearly was a whole lot brighter that Seattle. I remember the day well in Seattle, having walked to work, through pouring rain.
Bottom line, the Express won’t consume the Shadow
Hedge, (what weather people do!), the Nov 1 Express came through quickly; if the Dec 12th express stalls, (it isn’t supposed to), it might still consume the shadow.
Collateral benefit, it might stabilize the snow pack from future avalanches later in this season.
Wrap up December 13th; The Pineapple consumed the Shadow
While it was significantly drier than surrounding areas, it still rained .86 inches at the weather station in Sequim, pretty consistently from mid-afternoon Saturday through Sunday PM. The big wet storm from the south obscured the sky, (max solar barely breaking 100 w/m^2), and resulted in a couple of dreary days in the shadow.
Now some might argue that the shadow had a profound effect, with 12″ + precip totals over in Quinault, but from our perspective, if it “looks like a duck, it walks like a duck, it quacks like a duck, then it IS is duck”. Rain + Dark = Dreary. Strong Pineapple Expresses consume the Shadow, per our suspicion.
Also, take a look what all that precip did to the Dungeness River… in the new photo uploaded to our gallery.