Saturday, April 6, 2019

What Knocked Down 24 City Light Power Poles Near Boeing Field?

Something extraordinary happened Friday night just before 4 PM in south Seattle near  the Museum of Flight at Boeing Field.

A line of TWENTY FOUR power poles fell on East Marginal Way near the museum, closing the road, taking out power to tens of thousands of people, and striking a car (miraculously no one was killed).  Initial reports were that a tree had hit a power pole--in fact, the opposite occurred.


The map below shows the location of the museum and fallen power poles----keep the exact location in mind.

So what happened yesterday afternoon--why a catastrophic failures of two dozen poles in a row?  

Let's do the meteorological detective work.   

A well-defined front was moving through the region at the time, which is clear from a weather satellite image at 2 PM (see below).  Rain and blustery winds were in the forecast.

2 PM Satellite Image

Embedded within the front there was a narrow band of convection--a line of cumulonimbus clouds with heavier rain in which the winds were accelerated.  

To illustrate this, here are two radar images form the National Weather Service Camano Island radar at 3:45 PM and 3:54 PM on Friday afternoon.  The oranges and reds indicate heavier precipitation.  This line went through exactly when the power poles started to fall.  I suspect this is not a coincidence.



There is an extremely good weather observation location at the north side of Boeing Field, about 1.5 miles from the incident site.  The observations there indicate the heavy rain from the line and wind gusts to 29 knots---which is 33 mph.   Winds were southerly.



There are no weather observing sites immediately near the Museum of Flight, but there are some amateur sites with a few miles.  They also show winds gusts to around the same level as this line went through.  They also show sudden temperature declines and a sharp spikes in pressure (see below--look around 4 pm), consistent with a narrow cold frontal band in which frontal characteristics are concentrated.



The coincidence of the passage of this band with the failure of the power poles can hardly be an accident.   But the winds at nearby sites don't seem strong enough to take down properly maintained poles.   To me there are two possibilities:

1.   There was one pole (or several) that were rotted or weakened.  It failed in the moderate winds and took down the adjacent lines though the interconnected power lines.

2.   That the winds were stronger in the location of the Museum of Flight.

How could (2) happen? 

 On possibility is some kind of localized microburst, but that does not seem probable considering the modest heights of the convection and lack of dry air near the surface (which helps rev up the descending air from evaporative cooling).

Perhaps a more promising mechanism would be interaction with terrain. Boeing Field is in a valley with a sharp rise up to West Seattle to the south-southwest of East Marginal Way (see below).   Could the interaction of the strong outflow winds from the convective line with the topographic feature accelerated the winds?  It would take some serious numerical simulation to test this hypothesis.



___________________________________________________
NORTHWEST WEATHER WORKSHOP COMING SOON

Reminder:  The big local meeting for those interested in Northwest Weather is coming up:  the Northwest Weather Workshop will take place in Seattle on May 3-4th.   Everyone is invited but you have to register.   More information, registration details, and the draft agenda are found at https://atmos.washington.edu/pnww/.  A few presentation slots are open, so if anyone in the meteorological, fire weather, or associated communities would like to give a talk, let me know immediately.

23 comments:

Beeline said...

The key is "winds at nearby sites don't seem strong enough to take down **properly maintained poles**...". I have lived in Seattle for 35 years and have never seen so many downed electrical poles as I have in the last 12 months. Many sudden and catastrophic failures resulting in electrical explosions, power outages (of course), closed arterial roads, and danger to the community. My daughter's preschool was evacuated out an emergency rear exit after a wooden electrical poles snapped in half (in light winds) and closed all four lanes of Leary Way NW for several hours. Ten days later I saw two more downed electrical poles. All were unconscionably rotten throughout. I have since seen still more downed poles AND piles of brand-new poles in certain neighborhoods. This is another example of widespread infrastructure crumbling due to way overdue planning and maintenance. I am fearful that we will not continue to be so lucky with the results of such incidents.

Ansel said...

A small tornado perhaps, like the one that hit Port Orchard a few months ago?

c180tom said...

Cliff, ever since the Camp fire, I've been thinking about Quinault modelling done by UW Mets https://cliffmass.blogspot.com/2018/02/the-mystery-tree-fall-near-lake.html
This came to mind again on seeing the photo in your blog and the Seattle Times. I see it was the taller row of poles which were downed. (The shorter row had been previously “tested” http://www.ladder54.com/photos/plane2.jpg) by an insignificant Cessna…) (C: |
Where did the “domino” start? The south end of the tall poles is adjacent to the large Boeing 9-101 building so I’m curious about orographic effects of that. There are a number of other large buildings north of there. What might it take to get Seattle City Light to sponsor “some serious numerical simulation”? This might be provide useful guidance for ongoing pole condition monitoring and could provide some liability protection. PG&E might consider the same.

Kate Higgins said...

What about a Von Kármán vortex street wind effect on the blunt wooden poles with that front? I've seen a metal flag pole bend and break in a steady wind.

Jen said...

There was a burst of very strong wind on Mercer island at around 3:58pm. Strong enough that I called my kid who was coming out to the car and told her to stay in the building. A minute later it died down to nothing, never changed direction.

Westside guy said...

There’s another possible contributing factor... someone could’ve sabotaged the poles at some point with the goal of this happening during some future windstorm.

MAC in Bellingham said...

No idea what caused the utility poles to topple, but it looks like a big miss by the NWS on its 4-6-19 wind forecast (as well as the UW wind model that at least one local TV station uses). The NWS canceled the wind advisory after it become clear not much was happening. A few of the usual exposed areas on the coast and in the straits got some gusts, but that was about it as far as I can tell.

DMcL said...

Perhaps a harmonic effect induced onto the wires by the wind that amplified the stresses on the poles?

Carl Costenbader said...

I was noticing in one pic a wood pole was splintered like it had been hit by lightning. That could have started the domino effect.

Jonathan Doe said...

Cliff, you surprise me! Data? Simulations? SCIENCE?? Preposterous! All we need to solve this weather mystery is passionately ill-informed assertions and without doubt the culprit in this (and every) case is GLOBAL WARMING! I'm shocked that the obviousness of this conclusion seems to elude you. For shame.

Jonathan Doe said...

Power pole: "I've got a fever! And the only cure...is more creosote!"

Anthony said...

I work at Boeing directly in front of where the power lines went down. The rain came out of nowhere coming down really hard and the wind picked up sending the rain sideways. Boeing security all said lightning hit the pole and it came down bringing the other poles down long with it.

JordanP said...

Remember that these are 90’ tall poles as well, not the 40’ poles we have in the neighborhoods. A strong gut that far up is going to have significantly more leverage than on a normal pole.

c180tom said...

-Anthony notes that Boeing Security reported lightning.
-The Weather service (per Seattle Times) said there "were no lightning strikes."
-The Cooks (in car hit by pole)"..heard a boom and saw a flash."

How accurate is whatever NWS uses for reporting lightning strikes? It would be nice to rule out lightning before encouraging "some serious numerical simulation", but I'd love to see that anyway.

Sharon said...

Cliff,

Very interesting! I like your weather related event deductions and most of the comments. Keep doing them!

You should be proud of your good work, in general, not to mention on your own private blog.














SAR said...

I drove past the site tonight, saw at least 6 of the power poles where they broke, some at about 12 feet from the ground, a couple at about 6-9 feet and one just 3 feet from the sidewalk level. Very strange to see, but there is a sort of channel between Boeing buildings where a gust could pick up velocity as it travels to the east. The fact that some Boeing employees and security personnel said they saw a lighting strike is pretty much the smoking gun here, though, if you will.

Those poles did not look rotten to me, in fact appeared to be in decent condition. Maybe it was some sort of secret Manhatten Project deal Boeing Defense allowed to get out of control? Lol..

Quixotix said...

High wind gusts seemed like a good explanation to me, but these videos don't seem to show them:

https://www.king5.com/video/news/local/power-pole-falls-on-car-near-tukwila/281-b5e118f8-486a-4904-b51a-de736f651afb

Neither the tree in the first clip or the bicyclist in the second show signs of high wind gusts. Of course, with 26 poles down, a wind gust could have hit the poles further away.

waded said...

March 1, 2015 lightning strike took out tallest tree in uw arboretum:
https://botanicgardens.uw.edu/about/blog/2015/04/01/exploding-trees-now-showing-at-your-local-
arboretum/
Simplest explanation of the epic E. Marginal fail: lightning strike vs big possibility compromised poles

williwaw said...

Looking at the king5 videos I agree with Quixotix... it looks like a surprising lack of wind in these two scenes. However, at the 25 second mark (clock time 3:50:08 and in the 2nd location) there appears to be a flash. It occurs after the pole starts moving but before it falls. Maybe lighting, maybe arcing from wires or transformers? The first scene in the clip starts at about 3:50:10, ie., after the time of the flash in the 2nd.

Unknown said...

The timing and location of this event, in regard to Boeing and the recent developments of their Max 8 mishaps, makes this incident all the more suspicious and interesting, to me at least.

AndrewM said...

Tukwila police released video from 2 different angles & locations. There's clearly a lightning flash in both just a second before the poles fall.

https://www.seattletimes.com/seattle-news/third-party-will-investigate-sudden-collapse-of-wooden-seattle-city-light-power-poles/

JCalvertN(UK) said...

The poles are 90 feet high - not the usual 60 feet high. Yet the thickness is the same as your basic neighbourhood power pole.

They appear to be spaced further apart as well. So they were probably seriously overloaded to begin with.

Then, if you look at this Streetview very carefully, you will see that they were already leaning quite badly whenever the Google Streetview camera last passed down that road.

https://www.google.co.uk/maps/@47.5201144,-122.2990253,3a,75y,346.27h,91.48t/data=!3m6!1e1!3m4!1sRF2kyOgYJ490CuRUlaBXVw!2e0!7i13312!8i6656

SAR said...

Good work spotting those poles that were leaning. It looks like there were guy wires on only a couple of the 26 that broke. It's makes more sense now to consider that a combination of an abundance of pre-tension along with a micro-burst might create enough force to cause the domino effect here. Now we have to decide if a wind gust alone is responsible for the Crane collapse (and tragic loss of life) on Mercer this afternoon. How strange!