April 28, 2019

The Meteorology of the Seattle Crane Collapse

Important New Information:  An unofficial report from the weather station at the very close Center for Wooden Boats noted a gust to 35 mph at 3:26 PM on Saturday.

A crane collapsed in Seattle around 3:30 PM yesterday (Saturday) at the site of the new Google facility (Fairview and Mercer).  Tragically, four people lost their lives and several more were injured.

The failure was coincident with the passage of a wind shift and surge in winds associated with the southward passage of a Puget Sound convergence zone.   This wind shift/strengthining was associated with a dark cloud feature and some light rain...something that was evident from a sequence of images from the Seattle PanoCam ( a sequence from 3:10 through 3:40 PM is shown below).

The weather radar image from Camano Isl at 3:26 PM showed light to moderate precipitation associated with the convergence zone.

While the Doppler radar velocity indicted a strengthening of the wind (gray color indicates little velocity towards or away from the radar, the light yellow about 20 kt).

One of the nearest observing sites was near Eastlake Ave. (see map--the oval is the accident site)

 The observations at this site showed a gust to 25 mph just at the time of the incident.  The winds were from the north.  Look at the temperature trace (red line).  There was a large (roughly 10F) drop)in temperature with the wind event--consistent with the increase in clouds and onset of precipitation (note that the dew point (green line) rose at the same time, consistent with a moistening of the air).

Even better perhaps was a site right on the lake (see map)..

Its winds gusted to 23 mph around 3:30 PM.

Other nearby sites were consistent with this wind evolution, but slightly weaker.  The site in question could have had stronger winds (5-10 mph more) because it was upstream of the relatively smooth/low drag Lake Union.

The development of strong northerly winds on Saturday afternoon was expected, with the model and NWS forecasts clearly predicting it (see sample below).  Seattle WindWatch was sending out messages for days.
I will let others evaluate whether an increase in winds to around 30 mph should have taken down the crane.


The Northwest Weather Workshop on May 3-4

There is one local gathering each year in which regional meteorologists and interested layman get together to talk about our weather and its impacts:  the Northwest Weather Workshop.  This meeting is open to everyone.

The workshop this year will be on May 3-4 at the NOAA/NWS Sand Point facility in north Seattle.

The first day will include a session on Northwest wildfires--their prediction, the smoke, the associated meteorology and more.    That evening there will be banquet and a special speaker from Washington Department of Transportation, talking about dealing with the cold and snow in February.  Saturday will have sessions on OLYMPEX (a weather field experiment in the Olympics),  advancing weather modeling, the cold/snow of February, and much more.  Lunch Saturday is included in the modest registration fee.  There are special rates for students.

Typically, about 120-150 folks attend the meeting, which is held in Bldg. 9 of the NOAA Sand Point facility just north of Magnusson Park.  Folks often want to know where you have to be a meteorologist to come.   My answer is that 70-80% of the talks should be perfectly accessible to lay people.

You can view the detailed agenda here.  If you want to go to the meeting you must register in advance.  To register or learn more about the workshop, please go to this website: https://atmos.washington.edu/pnww/


  1. If I remember right, the design wind speed for the area starts at 85 mph, and the design must allow extra for local variables. Several witnesses have said the crane was being disassembled, though the company has declined to confirm or deny it. If that's the case, it could have been much more vulnerable at a given moment.

  2. Thank you for this post Dr. Mass. Perhaps such posts and condition evaluations will get responsible managers to check the tools we now have and take appropriate precautions.

  3. There is an eye witness report in today's Seattle Times. A 20 year old guy (Australian, in Seattle for cancer treatment) and with some background in construction cranes reporting and with a photograph of the tower leaning. It seems quite possible that a leaning crane could be more vulnerable to the wind than a correctly vertical one.

    Also, shouldn't a leaning crane be reported to authorities, and roads and sidewalks closed until it is vertical? And given what happened in Bellevue buildings evacuated as deemed necessary by the fire department?

  4. KOMO's photo gallery (https://komonews.com/news/local/gallery/crane-falls-on-multiple-cars-on-boren-and-mercer-blocking-eastbound-lanes#photo-1)

    YouTube video showing a Toronto construction crane being dismantled (https://www.youtube.com/watch?v=LUQalhFFnOE)

    A large blue mobile crane is visible in some of KOMO's pics (#7, 8, & 10), seems to be a smaller version of the one in the Toronto video. It's most likely there to dismantle the construction crane. The scattered yellow crane pieces were the tower crane itself. Risers, turntable, cab, and boom parts are visible in the photos, so the dismantling hadn't gotten very far.

    They're doing the job in light winds in the video, but even so you can see a loose piece being shoved around by the wind, about 3:00. I can only imagine what some sudden sharp gusts could do.

  5. Expanding on Richard's comments and noting that the windy conditions were in the forecast it would be reasonable to consider restricting crane disassembly if it is fore cast to be windy.

    1. Good luck getting a boss to halt work based on a forecast. Most will look outside and say, “looks fine to me”. Until it’s too late.

  6. Cliff, in Bellingham, with low humidity (<35%), dew points currently below freezing, clear skies and calm winds. Are we looking at potentially subfreezing overnight minimum temperatures? The minimum temp this morning was 34F which equalled the lowest temperature I've measured so far this month which occurred during the beginning of the first week of April.

  7. Hey Cliff -

    I work at The Center for Wooden Boats in South Lake Union and we actually have a weather station on our roof, which is probably the closest one. I looked at the data from the 27th at there was a high recorded gust at 3:26pm of 35mph. Unfortunately I didn't take a screenshot and I can't figure out how to pull reports that have more than one data point an hour, but it I can still see a record of the 35mph gust at the 4pm data point for that day. www.cwb.org/weather-station

  8. I would be focusing on the ground-based crane being used to remove the construction crane. The wind may have caused the ground-based crane to rotate, striking the vertical structure of the crane being removed. This may have resulted in the vertical structure braking and falling to the ground.

  9. You can get spot weather forecasts for these operations just like we do for controlled burns on National Forests. Posting lookouts is a good idea as well.

  10. Tower cranes when fully assembled are designed to weathervane with the slew brake off. The counterweight is head on into the wind. The entire weighted structure in compression is part of the tower's strength. So, yes when fully assembled it can survive thunderstorms etc. When coming down its vulnerable.

  11. I was driving up to the store on the King Snohomish County line on Saturday at around 3:30 when I saw an amazing formation of Mammatus clouds to my south. I pulled the truck over as had to take a photo. ( would love to send these to the blog if I can find out how). I snapped 2 more up the street. These clouds were moving and boiling to the naked eye. They were moving fast from NW to SE
    and were gone in about 7 minutes. I also was up in Edmonds from 10 to 2:20 pm and watched several cells heading from NW to SE. Around 2:15 pm, the convergence zone was definitely south down in Seattle with very dark clouds and precipitation seen and a curious phenomenon occurred where the wind died down from strong NW to weak SW and the upper level clouds moved north even as the parent cell was still moving south--on outflow so to speak. So given this and the Mammatus cloud formation I observed, there was a very strong cell/convergence with upper level pressure dynamics that was undoubtedly in my opinion, a causal factor in the horrible collapse. Also it was curious to see a picture in the Seattle Times Sunday in the Northwest Section showing a kayaker with her kayak under water. How often do you see that? There was some big waves kicked up very rapidly to cause that, and the kayaker was in south Lake Union. Coincedence?? I don't think so.

  12. A crane ought be able to take winds of at least a hundred miles per hour. As far as I'm concerned the weather was NO excuse. The crane company AND the city should pay. And in any case, Seattle allows far too many of these projects at one time.

  13. I've seen a dash cam video. The crane accident was not a wind event. There was something else going on with the foundation or a lower tower section.

  14. As a member of local 302 I can say the crane operators are responsible for it's safe operation. They are The Experts and totally committed to %100 safety, all the time. BUT, I can't understand why the tower would be leaning, even slightly. The answer probably lies there. Perhaps the disassembly of the base happened ahead of schedule. It should have been even more stable being half dissembled... Perhaps the wind kept the mobile crane from making a clean pick of the crane being removed. condolences to all affected.

  15. Amazing cumulonimbus forming right now over the north central Cascades with anvil tops. There are going to be some thunderstorms this evening...

  16. Wind shifts can of course be very dangerous for fire suppression crews, and your blog of April 2019 about the situation in Twisp was poignant. At least someone is paying attention today during another fire season July 22, 2021:



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