1st East Wind “Event” Of the Season This Weekend

October 11, 2018

9pm Thursday…

You’ve probably noticed; we have entered a remarkable period of mid-October sunshine!  Today was totally sunny except for some spots of brief low clouds and/or fog.  The next 6 days should be mainly cloud-free, or just plain sunny as you can see in our 7 Day Forecast (which you can always find here)

7 Day Forecast Graphic 2017

The reason is a strong upper-level ridge shifting from the eastern Pacific directly over the Pacific Northwest.  It’s going to stick around for quite a long time.  Here’s the forecast from GEFS (GFS ensemble system) for Monday.  Lines are upper-level heights, colors are the anomaly (red = above normal, blue = below).

gefs_mon_am

Then next Wednesday from the EPS (ECMWF ensemble prediction system)

eps_wed_am

The ridge appears to be strongest at that time.  Looking farther ahead is stretching the limits of weather forecast models, but most interesting is that they all show a similar setup through Day 10…NEXT weekend from the EPS.  Not quite as extreme, but warmer and drier than normal.

eps_sun_21st_10days

So it appears that we are in a long (7-10 day) stretch of unusually dry and warm weather in the Pacific Northwest.

But there is a wrinkle to this forecast…not all of you will be able to enjoy the sunny & warm weather as much because of…the wind.

We’re quickly approaching the cool season (November-March) and that means “East Wind Season” too.  Fall and Spring feature the seasonal oscillation from westerly Gorge wind to easterly wind.  In this case surface high pressure drops down the back side of the upper-level high Saturday through the middle of next week.  Strong high pressure east of the Cascades will give us quite a strong pressure difference across the Cascades.  You can see it on the WRF-GFS surface map for Sunday morning.

wrf_sundayam

That’s 7 millibars easterly gradient from the lower Columbia Basin (near The Dalles) to Portland both Sunday and Monday mornings.  That’s a very strong east wind for October.   Plus, from Saturday afternoon through early Monday it will also be a “downslope” wind.  The layer of easterly flow is deep enough to move right over the Cascades and down into the valleys.

What does that mean for us?

Much of the metro area will be very windy Saturday afternoon through early Monday.  Expect gusts 20-35 mph in the windier spots with gusts at the west end of the Gorge in the 40-55 mph range.  Probably a few scattered power outages as well…under sunny & blue skies.

Of course Crown Point will be a bit stronger…maybe gusts 60-65 mph for the first time this season.  Those highs in the upper 60s will feel quite a bit cooler out there in that wind!

You can see this on the WRF-GFS time/height cross-section over Portland.  Time goes from right to left.  Starting at 5am today (right side) and ending 5pm Sunday on the left.  You see a few 50 kt speeds around 2,500′ over Portland Saturday night and Sunday AM.  That’s impressive even for winter!

kpdx.th

The pressure gradient will drop off a bit Tuesday & Wednesday confining wind to the Gorge.  At that point temperatures will likely peak here in Portland as the wind backs off.  We should reach mid-upper 70s on those days.

Enjoy the sunshine Friday and into the weekend, but be ready for things to blow around a bit too!

Chief Meteorologist Mark Nelsen