Soaking rains, mountain snowstorm, and a “Pineapple Specific” as December arrives

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  • Mild rain arrives Thursday, then extra typical wet/windy climate Friday. Then again to off/on showery climate Saturday
  • Precipitation Thursday will seemingly fall as snow east of Bonneville Dam within the Gorge. Anticipate little or no accumulation at river degree however a pair inches might accumulate up round 1,000′ on the market for the primary time this season. I doubt pavement on I-84 will flip snowy…simply not that a lot precipitation and barely chilly sufficient this time round.
  • Mild snow begins falling within the Cascades Thursday, then ramps up into Friday. Most fashions are producing a really heavy snowfall Friday night into Saturday morning. For that reason we’re calling that interval a potential FIRST ALERT WEATHER DAY within the Cascades for heavy snow and blowing/drifting too. A Winter Storm Watch is up throughout this time in fact. Pay very shut consideration if you happen to plan to journey by means of the Cascades Friday evening.
  • Lastly, a “Pineapple Specific” will probably be aimed toward Cascadia Sunday by means of not less than Tuesday. Consider it as a “subtropical firehose of rain” that soaks varied components of southern British Columbia right down to southwest Oregon at completely different instances throughout that interval. This will probably be a heat and moist interval with solely rain falling even within the excessive Cascades. At this level it doesn’t seem anybody a part of the area will get sufficient rain for widespread flooding, however we’ll be watching carefully! By the best way, a Pineapple Specific is identical as an atmospheric river, however the heat model. We began utilizing the time period atmospheric river prior to now 20 years or in order understanding has progressed.
  • Gusty southerly wind is probably going on the shoreline and western valleys, primarily Friday and Sunday. At this level we don’t see a windstorm, simply typical gusty south wind.


First, some gentle snow within the central/japanese Gorge Thursday. The low degree airmass within the Columbia Basin of Oregon and Washington has cooled beneath a heat upper-level ridge. This “chilly pool” has turned colder the final two days and isn’t going anyplace till a westerly wind arrives Friday. Right this moment Hood River and The Dalles solely made it to the mid-30s. When (very gentle) precipitation arrives noon/pm Thursday, this tells me it’ll be within the type of snow. In reality the WRF-GFS forecast sounding for 1pm Thursday is a snow sounding; something to the left of the yellow line is beneath freezing. Solely alongside the river will it’s above freezing when the snow arrives

Increased up within the White Salmon, Hood River, and Wind River valleys I might see as much as 2″ falling by Thursday evening. However moisture is restricted; one more reason I believe it’s unlikely I-84 turns icy and snowy.

Wx Weblog(Mark Nelsen | kptv)

850mb temps are proper round zero Thursday by means of Saturday, so anticipate a 3,000′-4,500′ snow degree throughout this occasion. A moist snow at/beneath passes. How a lot snow by means of early Saturday? Our GRAF mannequin doesn’t exit that far, however the Euro and WRF-GFS look about like this…not less than 15-30″. Discover the Blue and Wallowa mountains get nailed over in northeast Oregon too!

(Mark Nelsen | kptv)

A greater breakdown of driving situations within the Cascades…Friday evening certain appears to be like just like the worst of the occasion


The ECMWF ensemble system was upgraded to the next horizontal decision final spring which handles terrain significantly better. You possibly can see extra element right here, however the identical common thought, possibly 2-3″ throughout these three days.

For that reason, I don’t see a setup but for vital flooding or damaging wind within the western valleys this weekend by means of early subsequent week. BUT, if the atmospheric river sits over one location for 2 days as a substitute of transferring north and south? That might produce flooding. We will probably be watching carefully!

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