March 25, 2016

Avoiding Falling Trees During WIndstorms

During virtually every major windstorm that has hit our region, someone has died from a falling branch or trunk.    The chances of being a victim in any particular windstorm is extraordinarily low, but with millions of people in our region going about their daily lives, someone inevitably gets hit.

For the recent March 13th storm, the death was a man in Seward park.  For the November 17th windstorm, 3 people were killed by falling trees.   Today, the front page of the Seattle Times had a story criticizing the Seattle Park's Department, suggesting that they should have shut down Seward and other parks.

So lets examine this threat and what you can do to protect yourself.  First, whether trees or branches come down is more complicated than just wind.

1.  Early season storms do much more damage for the same wind speed.  Leaves on the trees dramatically increase the drag  and spring/summer growth has been untested by strong winds.   Our August windstorm was a great example of this, producing some of the worst tree damage in our region's history.

2.  Extreme dry conditions over the summer can make the trees more vulnerable.  That probably contributed to the extraordinary damage of the August storm.

3.  Very wet soils reduce the adhesion of roots to the soil and soften the soil, making tree fall more likely.  This was clearly a factor for the March 13th storm, which followed the wettest winter in Seattle history.

4.  Exposure is very important.  Winds are stronger near hill tops and downstream from water.   Wind blows more strongly over water since it is aerodynamically smooth, so being near the Sound or Lake Washington can bring increased devastation.  This certainly contributed to the tree fall in Seward Park, since it sticks out into Lake Washington.

As a general rule of thumb, falling branches can start occurring when winds start gusting above 30 mph and major tree damage occurs above 40 mph.

How to protect yourself!

Not a tree expert?  You can start by following the National Weather Service weather forecast--for the March 13 event they predicted strong winds and mentioned to keep away from tall trees.

But if you are more of a hands-on type of person, why not use the wind tool used by the professionals at Seattle City Light?   A web page they funded, created by my group (particularly Jeff Baars) at the University of Washington is available to all:  Seattle WINDWATCH?

WindWatch accesses the most skillful local weather forecast models and the latest National Weather Service forecasts, telling you whether strong winds are coming.  It plots the current wind speeds.  Check out the website and its substantial capabilities.

Have you ever noticed that Seattle City Light seems to restore power much more quickly than other local utilities?  One reason is that armed with the information form WindWatch they can stage their personnel and supplies better.

So if winds over 30 mph are being forecast and you want to minimize your risks (still very small), you would be wise to keep away from heavily wooded areas.  High on the list is the Burke Gilman trail (where I almost got killed last year!)  Tree-filled parks near the water are also dangerous in strong wind conditions (e.g., Lincoln Park, Carkeek Park, Seward Park).

Not a good idea during a windstorm

The stronger the winds and the earlier in the season and the wetter the ground, the more you should avoid trees.   Schools should keep students in the buildings when strong winds blow, even if the power fails.  Don't send them home.  A famous story is how Seattle high schools released their students during the height of the Inauguration Day Windstorm (January 20, 1993) because the schools had gone dark.    Very bad move.

If it gets windy and you have a big fir to the south of you, sleeping in a second story bedroom might not be wise.  Good time to camp downstairs.

Should Seattle close its parks during big windstorms?  Certainly, most of the commenters on the Seattle Times website were against it, suggesting it was classic nanny-state behavior. And lets be honest, the risk is very, very small, and many Seattle parks (like the Burke Gilman trail, the most dangerous in strong winds) can not be effectively closed off.

Furthermore, the great weather killer around here is not falling trees in parks, but car accidents during icy conditions or heavy rainfall.

So before closing parks, perhaps Seattle should develop a Seattle Environmental Hazard app for smartphones.  It will know exactly where you are from GPS and warn you if there is a threat from strong winds, icy conditions, flooded roadways, and much more.   And in the future, you could get earthquake warnings from the UW's earthquake warning system run by Professor John Vidale, or warning about potential landslide.

Such an app could save some lives. It could be free or could charge a minimal amount to help support Seattle's PRONTO bikeshare system, which is going to need lots of funds for a long time.

Reminder: don't forget to support KPLU!  They need to raise 7 million dollars by June 30th.  If ALL 400,000 listeners give $20, they can do it!   Contribute or get more info here.


  1. Great blog post as always. I'm opposed to Seattle closing their parks during any weather event because some parts of them can be safe and awesome places to go. A great example would be Lincoln Park during the last wind storm. Walking from the south end out to Coleman pool would be safe and spectacular. If Seattle closes the park, but then doesn't enforce the closure, they would likely be liable for not making certain people stayed out.

    Of course I did stop my son for heading out for his weekend walk during the storm as I felt it would be foolishly risky to be out walking towards Alki during that weather.

    I do like the app idea. It could be added on to on a regular basis for other information that could be useful for safety and convenience.

  2. Thanks for the earthquake early warning plug!

  3. Hey Cliff,

    Check out the UW radar loop at 10:48 AM today. It looks unusual to me. Thunderstorm? Anomaly?

    Thanks, Paul Henriksen, Lopez island.

  4. Hi Cliff. Great blog as usual. I wonder why the City Light people or whoever is responsible for dangerous trees doesn't do something about the large limbs over Ea. Madison from Lk. Washington Bl. east to McGilvra. To my untrained eye these lg. branches look like a widow-maker in waiting. Perhaps the trees are on pvt. property?

    Art Pasette

  5. How about a warning system at major park entrances that flashes red when wind gusts approach 30 mph. Similar to the 'fire danger' signs located along Vashon's main highway.

    Even after the wind stops, large branches hung up in trees can fall unexpectedly as the wind shifts or rain adds weight to the broken branches.

    Winds can gust over 100 mph in Boulder, Colorado. I had a good friend and class-mate who thought it was cool to go walking during a strong wind-storm. A tree toppled over and the large branches struck her back. She survived and mostly recovered. She was young and young people like to do dangerous things.

    After a good blow, it can take me several hours to days to clear all the large branches and trees from my drive, yard and a couple miles of wooded pathways. I'm still working on a large Arbutus (Madrone) tree that fell last December.

    I don't even let our dogs out when the wind blows. It's not ambiguous. When the wind gets going it literally rains branches and twigs with the occasional big crack and crunch as trees fall colliding into adjacent trees on their way to the ground.

    It's not safe to drive either. Cars provide little protection against large trees. Dark, hilly roads can hide fallen trees and live power wires. My neighbor was driving on the island and suddenly came across a tree fallen over the road. He swerved to avoid colliding with it and landed in the ditch with water up to his waist. Totaled his SUV.

    I love trees, got a tree-house, but like the ocean, respect it.

    I have dozens of wind stories. I grew up in the upper Midwest. Had a small border line F1 tornado run over our house when I was 10. Yes, it sounded like a freight train. Watched another one dance through a corn field east of Greeley, Colorado. Like my friend in Boulder, I stood outside and watched the darn thing, it was way cool.

    I was chasing storms on my bike then in my car long before they were professional storm chasers. Now that I'm old, I watch storms on radar and weather cams or sit on the back porch.

  6. i knew the guy who was killed. :(

    RIP, Eric

  7. Once again, the Seattle Times uses misinformation and hyperbole to try and impact policies. It's sad that's the paper that has lasted in Seattle.

    My deepest sympathy the family friends of the man who died.

  8. We lived for many year with acreage. Did not allow tall trees near the house, and we did not go where the alder section was during wind storms.

    Parks probably should just have signage that winds and heavy snows create danger near large trees. You are at risk if you enter under those conditions.

    National Parks are seldom sued successfully, wilderness dangers are assumed when you enter.

  9. Perhaps we should ask the city to cut down all the trees in every park and along every trail - you never know when one might collapse and hit someone. We could always erect new "trees" made of green styrofoam.

    And, while they're at it, perhaps they should mandate a several-foot-thick layer of foam be placed around all cars, busses and trucks - it might save lives.

    Also, we need to replace the hard pavement of all roads and trails (such as Burke Gilman) and replace it with something less likely to injure a person when they fall.

    I'm not anti-government... but I find the idea that the government can somehow protect us from any and all possible harm ludicrous.

  10. My cousin Jonny and his son died when a tree fell on their camping trailer some years ago. My kids walk a longish trail through high forest from the bus stop and during gusty conditions I am often checking your site or NOAA and debating whether to pick them up and stay downtown (Mercer Island) until it blows over, or let them walk through it. It is a tough call, winds seem to often be peaking around the afternoon. At least it feels that way to me. While no one has been hurt so far there have been many, many trees down this winter. I have been hit by a branch while waiting for them. It's one of those gray areas. It would be over-reacting to keep them home or down the trees, but it can be a dangerous situation and is a hard call.

  11. Seems like a little common sense is needed. Sad that some people seem to want to point the finger of blame Every time something bad happens. Government can't fix everything. Use common sense when the winds blow and stay away from potential hazards, keeping in mind that accidents can still happen when the greatest of care is taken.

  12. Actually, the threshold for tree damage used to be much higher - more like 60 mph winds. The real reason they are falling - and injuring people and property - so frequently now is that trees everywhere are weakened by air pollution. You can't see tropospheric ozone, but the background level is increasing as more and more precursors (NOx, methane) are released, and circumnavigate the globe. Ozone is toxic to people causing all sorts of heart and lung disease, asthma, cancer and even diabetes BUT it is even more poisonous to plants. Trees that are exposed season after season suffer cumulative damage and greater susceptibility to insects, disease and fungus - all epidemics around the world. See short film:


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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