Saturday, November 26, 2011

Why is Northwest Washington So Windy?

It seems like it occurs during nearly every storm.  Before a front or low center hits our region, one area gets winds first--and they are often very strong and from the southeast .  We are talking gusts about 50 mph and higher in the stronger events.  And then after the storm moves by, they get hit by powerful winds from west.

What is this benighted region, one in which Seattle TV stations often stage their camera crews for dramatic wind shots?

The answer:  Northwest Washington...the region extending north and west of Everett, over northern Whidbey Island, to the San Juans and down to the NE tip of the Olympic Peninsula.

Why is this region so windblown?  And why only certain directions? Why can the winds be blowing at gale force there, while Seattle is practically calm?  I will try to explain in this blog.  We have had a number of major NW Washington wind events this month and another will hit tomorrow (Sunday, 11/27).

Northwest Wind Land
I got my first personal taste of the NW Washington winds in the 80s while I spent the night at Rosario Resort  on Orcas Island.  The winds came up quickly that night and they were roaring!  Just heaven.

A mild event is going on right now (Saturday, 9 PM).   Here are the winds:

Calm in Seattle and Port Angeles.  Very light winds at Sequim and Victoria. 30 knot sustained winds at Smith Island and northern Whidbey Island. Gust over 40 mph.  These radical differences in weather over short distances are why we love Northwest weather!

Sunday morning things will really be blowing: here is the lasted WRF model forecast of sustained winds at 4 AM.  Sustained winds of 40 kts (46 mph)...with higher gusts, of course.


 So why the strong winds?  One reason is the extensive amount of water in the area and winds blow much stronger over water because it is aerodynamically smooth.  But there is something else....the OLYMPICS!.   The mountains distort the local pressure field, with pressure being increased on the windward side and decreasing on the leeward side.  The winds in these situations are almost always from the south...thus there is high pressure on the southern flanks of the Olympics (rising air causing cooling and cool air is more dense and thus results in higher pressure) and lower pressure (leeside trough) on the northern side where air sinks and warms by compression.  Here is a graphic of the situation at the same time as the previous figure...the lines are isobars (lines of constant pressure) and the wind barbs are shown too.   See the distortion of the isobars by the Olympics?  Nice lee low by Port Angeles and Sequim.  Do you see how the distortion caused the isobars to bunch up from roughly Everett to Whidbey Island?  Such a large change in pressure is called a large pressure gradient.  That causes the winds to accelerate greatly as the air moves from higher to lower pressure....and is the essential cause of the strong winds observed tonight and on Sunday....and many other times!


You need good southerly flow approaching the Olympics to get this effect...and such southerlies often precede a strong front or accompany an approaching low that is headed to the north of us.  In fact, when a low goes north there is a background south to north pressure difference that can really add to the strength of the southerlies forced by the Olympic effect noted above.  Here is a larger scale view of the pressure situation tomorrow at 4 AM... a strong front IS approaching.


Just to show how windy Smith Island (just west of Whidbey Is) can get, take a look at he recent max gusts there.  Lots of 35-40 kt gusts the last day and nearly 60 kts on the 24th.


But wait until tomorrow morning! You can check the winds yourself at this site:

http://www.ndbc.noaa.gov/maps/NW_Straits_Sound.shtml

10 comments:

erg67 said...

Rosario is still open.
http://www.rosarioresort.com/

windlover said...

Hi Cliff ~ Another place that gets hammered with SE winds is Eatonville. A good example would be Thanksgiving. We had gusty winds all morning into the mid afternoon. They were sustained at about 20 with the highest gust of 52. We went to my sisters for dinner near Kent and there wasn't even a breeze until later in the afternoon and even then it was only a breeze...maybe a gust to 20. Yesterday morning the gusts were only 36. Today the winds started around 3:30 a.m. (with a temp. of 62!) and they are still gusting to around 40. There are many times when we get hammered with gusts to 50 or 60 while the Seattle area is still waiting for the wind to arrive. When the winds die down here, they are picking up in the Seattle area. And I chuckle as I watch the news and they make a huge deal out fof the 30 mph gusts they are getting! The only exception is when the storms come in from the north and come ashore too far north. Then we don't get much. But when they come up the coast from the south we get hammered! I love a good wind storm....I hope we get more this year!

jdrlopez said...

Appreciate the explanation for the high winds. I live in the SJIs and have wondered about an associated phenomenon - can you explain why is it that when we get those very strong winds there's no rain? It's either wind OR rain but not both...we see this in the radar maps as a donut hole, more specifically weather situational than the general rainshadow climate effect. For example yesterday it was windy and dry but today it's the reverse.....it started raining early this morning when the wind dropped.

Ferdi said...

Thanks for drawing attention to our windy corner of the state Cliff. For years I've complained to the weather service that they were being too conservative in their wind speed forecasts for the San Juans. They've been right on the money this year.

Here on Sinclair Island we get blasted from every direction. Large bodies of water surround us. Toward the SE there is little topography even where there is land. Towards the north nothing but water clear to Canada. And then arctic outflow winds funnel down the Frazier River Valley occasionally basting the area with hurricane force winds. So all in all, it is a very windy place.

John Davidson said...

Living in the San Juans and being a sailor I pay a lot of attention to the wind, thanks for clearing some things up for me. Since Thanksgiving day we've had one storm after another, with one nice sunny day thrown in (Friday). We are on the NW corner of Blakely Island and are protected from the SE winds (they curl around the island and we actually have a NE wind at the house during a SE gale) but we can see the whitecaps in Eastsound as they race toward Rosario (which is open by the way) and the town of Eastsound.
The NE winter storms are the ones that hit us hard with the frigid winds from the Fraser Valley.

C&A said...

Here near the western shore of North Whidbey, it sure can be wild. Last night/this morning was a good storm.

Cliff I would love info on the westerly gales that seem to follow some storm fronts. It seems like these can be just as strong as the southerly winds, and they are often a big surprise, not really announced by the NWS forecasts.

Tony said...

Are these wind barbs off the coast really correct, so many lined up exactly south to north? I understand some deflection from the Olympics, but over such a large area?

Mark said...

Cliff - first of all, I hope your pup is in good hands and finds its way home!

Secondly, the other weather blow is the "Chinook Winds" over the I84 area of the Columbia River gorge. The pressure difference between The Dallas, Hood River and Cascade Locks sometimes is amazing. And when it's high pressure in Eastern Washington, watch out East Portland!

A good follow up article to the Olympic Mountains...

iancruickshank said...

Here in Victoria, just across the water from San Juan Island, I've noted exactly the same coincidence as "jdrlopez" mentioned: very often, during frontal systems with SW flow aloft, it will be dry here while there are strong SE surface winds, and then rain begins at the exact time that the SE wind eases off. It will often switch back again to strong SE wind as soon as an hour or two later, and far more often than not, the rain eases off exactly as the wind returns. If there's a pronounced dry "donut hole" in the lee of the Olympics, the western edge of the "donut hole" will often shift slightly eastwards and westwards across Victoria (and across the San Juans), and very often, the western edge of this dry slot seems to coincide very closely with the western edge of the plume of strong SE winds. I think that a lot of what we're seeing here might be linked to slight changes in flow direction/pressure slope, where with just a slight westwards shift in the upper level winds the western edge of the Olympic rain shadow shifts eastwards, and at the same time the surface pressure gradient shifts slightly westwards as well, shifting the eastern edge of the Olympic wind shadow eastward and shutting off the SE winds. So, the question then is, with strong SW flow aloft, strong S/SE surface flow, and a well-marked Olympic rainshadow, why does the western edge of the rainshadow donut hole often coincide so closely with the eastern edge of the Olympic wind shadow? Is it just coincidence of how the Olympic mtns topography affects both rainfall and surface winds, or is there some sort of forcing by the plume of strong SE low-level winds that effectively holds off the western edge of the well-marked dry zone at times? It's uncanny how often this either/or SE wind/dry versus rain/light wind coincidence happens; I've seen it time and again here for years. Of course as frontal systems pass, the flow aloft often shifts more westwards and the surface winds go to southwest, and here in Victoria we'll often get most of our rain in this later part of a frontal system's passage and in post-frontal showers, when there's not nearly as strong an Olympic rainshadow effect here. And with westerly flow aloft, the often rain-shadowed southern portions of the Victoria area can get very significant rain as the moisture flows down Juan de Fuca strait with little shadowing at all.

On another note, Env. Canada seems to often over-forecast strong SE winds in Victoria; I've seen many more times that a prediction of SE 50-70 kmph turns out as light winds here than the other way around; it's often blowing strong just to the east, over the San Juans/Bellingham/Whidbey Island, but Victoria sits just west of the plume with light N/NE winds or much lighter SE winds.

Fascinating stuff...I'd be interested in any comments Cliff or others might have!

-Ian C.

Sail on MIke said...

I had a memorable experience with winds in this area. It was several years ago and we were camped in the winter with a bunch of boy scouts in the state park right by the Keystone ferry on the Whidbey side. There was a wild storm that night (predicted). There is a ridge above the campground and the wind literally sounded like a jet engine blowing through those trees. It was plenty windy even in the campground but nothing compared to that ridge. What a wild and memorable night. A highlight for sure!