A Very Wet Weekend Ahead

October 19, 2017

7pm Thursday

It’s been a classic wet Pacific Northwest day.  It’s not like we’ve seen massive downpours, but it rained just about every hour of the day.  Expect the same tomorrow as waves of showers move inland behind today’s cold front.  One difference tomorrow is that we’ll see sunbreaks between the showers; it won’t be such a gloomy day.

But this weekend is a bit different.  All models forecast an “atmospheric river” (another name for a Pineapple Express) aimed somewhere near the Oregon/Washington border from Saturday through midday Sunday.

GFS Water Vapor

GFS Water Vapor2

I’m very confident it’ll be aimed somewhere within 100 miles north or south of that spot, but exact location of the deepest subtropical moisture is critical in determining how much rain any one part of our region gets.  As always the heaviest rain will be in the Coast Range and Cascades.  Models are in pretty good agreement that this is going to be a very wet event.  They have consistently been forecasting 8-10″ (or a little more) in the usual wettest mountain locations.  Here is the morning ECMWF rain forecast:

ECMWF Precipitation Accumulation

Once again (for maybe the 4th-5th day) it’s showing a maximum of 10″ or more in those usual extremely wet spots.  That would include a few of the western Coast Range slopes and SW Washington Cascades.

If we indeed do see 3″ of rain from Saturday morning through Sunday midday, I think we could get some urban & creek flooding.  Especially Saturday night and Sunday morning since precipitation intensity appears to be highest during that time.  So keep a close eye on the forecast this weekend!

By the way, I just noticed snow has begun sticking at 5,000′ on our Skibowl camera.  The snow level drops to Government Camp by morning and stays there through Saturday morning.  By the time the snow has changed to heavy rain late Saturday morning we will have seen another nice dumping on the mountain

Snow MtHood Outlook

Much of that will be washed away later Saturday and Sunday of course so this sure won’t mean an October start to the ski season.  But it’s always nice to see early snow.

Chief Meteorologist Mark Nelsen