Wednesday, January 1, 2020

The Space Needle Fireworks Dilemma

A wonderful Seattle holiday tradition was cancelled last night:  fireworks launched from the Space Needle.  The reason?  Strong winds.

Picture by Wonderlane

According to the rules established by the Seattle Fire Department, Space Needle fireworks are considered too dangerous if the sustained winds are greater than 25 mph or maximum gusts exceed 30 mph.

The Space Needle folks have a Davis weather station mounted right below the upper deck, which reported sustained winds of 34 mph with gusts to 45 mph at midnight.  Thus, no show.

But now we get to the dilemma part of the blog:  folks in the crowd reported weak winds at the surface, something confirmed by Space Needle personnel, who had a hand-held anemometer (which measures wind speed) at the ground.

Local observations near the surface showed wind gusts ranging from 10-15 mph away from the water, to immediately 20-25 mph downwind of water. The hand-held anemometer reported about 10 mph (roughly 5 meters per second)



So why were the winds so strong at the Space Needle observation deck (around 600 ft above the surface)? 

 It is all about height and exposure.    Winds tend to increase with height.  Why?  Because the Earth's surface is rough, with trees, buildings and other obstructions that tend to cause drag or friction, and thus slow down he wind.  That is why winds are generally stronger over the water....less "stuff" too slow the wind.

As one gains elevation and gets above these features, the drag declines and the wind speed increases--often substantially.   Meteorologists have various tools to extrapolate winds in the vertical, finding that in well-mixed situations like New Year's Eve, a log or power law fits observations quite well.  Doing such a calculation, I found the winds could have quadrupled between the ground and the Space Needle observation level.  Seems quite reasonable

If you like to play with this yourself, there is an online calculator here. (you can see my choices at the end of the blog).  And there is one other factor to consider:  for southwesterly winds (as were blowing above the surface last night, winds reaching the Space Needle were off the Sound, where there is less drag and winds are generally stronger  (see view from the Space Needle below).


So the bottom line of all this, is that in an urban setting with lots of blocking buildings and trees, the wind can increase very rapidly with height as you rise above the blocking features.  So it is not surprising, that the crowd at ground level did not experience strong winds while the winds were howling 600 feet above.

I was as disappointed as anyone that this tradition was cancelled (the first time in 30 years), but the winds greatly exceeded the Seattle Fire Department's criterion, and they are responsible for keeping everyone safe.
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23 comments:

  1. Fire works look nice, however perhaps we need to reconsider their enviormental impact and carbon footprint. That money could be allocated for more practical and beneficial use such as homeless shelters.

    Laser and drone light shows could become the new tradition.

    Out with the old and in with the new (paradigm).

    https://www.terrapass.com/fireworks-impact-environment

    Chris H.
    Heli-free North Cascades

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    1. Hmmm I don't know.. could it be possible that the laser lights cost more than the fireworks, not less? If that were true, then what would we do? Maybe the city can assign someone to check into this.

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    2. Drones wouldn't be able to fly in winds of more than 1/3 their top speed. For lighting shows this would only be 10mph.

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    3. I'm just very happy we have an en pointe fire department who won't endanger the Emerald City over some fireworks. They're great, but we liked the light show just the same.

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  2. The surface was also sodden after several days of rain, which lowered fire risk substantially. Blind adherence to a rule lacking nuance seldom produces optimal results.

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    1. It was people's safety not the risk of a brush fire. It's always damp in January in Seattle. Not sure what you're assuming but keep it to yourself. Simple man simple Dan

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    2. I would imagine the issue is not fire risk in a downtown setting, but embers landing on people far from the launch point.

      They are hot.

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    3. Thanks, Anonymous. In the future, I'll make sure to check in with you first before daring to voice an opinion.

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    4. Dan,

      I work with professional fireworks. There's two reasons why wind is a factor in shutting down shows, regardless of whether the ground is dry or wet.
      1) The "fallout" area (where debris from exploded shells could land) becomes huge and unmanageable. With 40 mph gusts, you'd have a fallout area stretching across North Seattle.
      2) The wind deflects the fireworks as they are flying through the air and it reduces the altitude above the ground they are able to achieve. In strong winds, that makes pretty much all your shots "lowbreaks" or fireworks that go off close enough to the ground that their embers haven't even gone out before hitting the ground. And in the particular case of the Space Needle, this means that fireworks fired into the wind will blow back and explode on the Space Needle itself.

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    5. How you gonna attack someone and be anonymous..you are a dou@$%bag for sure

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  3. I was hoping to see the fireworks from the 41st floor roof deck of the apartment tower just east of the Space Needle (at Denny and Terry), and the wind definitely started gusting around 11:50pm. (Most people who were waiting outside went inside until 11:55pm.) The few clouds that were still over downtown were moving very fast, providing a good visual indication of the wind speed. On the video I took around midnight, the wind noise is very noticeable. While I was disappointed that the fireworks were canceled, it is understandable given the wind gusts around midnight.

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  4. Perfectly understandable why they did what they did. That said... the light show was rather underwhelming. Guess it's the best they could come up with on such short notice.

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  5. This explains why my previous 58th floor workspace swayed so much. My pens would end up on the floor.

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  6. I didn't miss the fireworks. Also, heard far fewer around my neighborhood than in years past, despite dry conditions and calmer winds here. Maybe a sign of things to come.

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  7. The former World Trade Center twin towers used to sway quite a bit. Eventually on a particularly gusty day the two would get out of rhythm with each other which gave a very disturbing illusion of extreme sway if looking out the window from one tower to the other. At 1300+ feet, the wind could be very strong with no other buildings to mitigate it.

    Its a bummer about the fireworks but its better to have some sour grapes about the let down than an incident where injury or property damage occur.

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  8. Thank you for the post. Still makes me laugh that people couldn't naturally draw this conclusion on their own. It's never going to be windy below when surrounded by a mass of people and buildings. Critical thinking needs to be amplified in elementary school

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  9. Burj Khalifa never has problems with wind and fireworks at new year... "Safty frist" now is beaceam as perfect excuse if do not know what you are doing but still whant to bee coled "professional" or "expert"

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  10. 38 m/s is equal to 85 mph. It's looks like this theory is not working...

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    1. Baubus...the ratio is right. I redid it changing the surface speed to something more reasonable...get a very realistic wind speed. So I think we are good...cliff

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  11. Cliff, Thanks for the explanation! Let's see what happens next year. I am open to drone light shows if feasible. However, Skunk Bay weather videos of nature's show are my favorite. It's encouraged me to look to the sky more often to take in its dynamic beauty.

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  12. "That is why winds are generally stronger over the water....less "stuff" too slow the wind."

    For my local situation, that would read, "That is why winds are generally stronger over Moriarty, New Mexico ... less "stuff" to slow the wind."

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