Monday, October 12, 2020

The Moclips Tornado and the Intense Front that Spawned It

There is something about the western side of the Olympic Peninsula that brings big trees down.  

In 2018, a swath of old-growth trees fell near Lake Quinault from an intense mountain-wave rotor circulation, something described in a paper I wrote with some UW graduate students.  There were some we didn't convince, including repeated claims of UFOs and military intervention.

And on Saturday morning, around 4:45 AM, a weak tornado brought trees down along the Moclips Highway, between Moclips and Lake Quinault (see picture taken by the Quinault  Assistant Fire Chief).

This event occurred when a very strong narrow cold frontal rainband made landfall on the coast.  And we have a very good view of the action because of the National Weather Service Langley Hill radar, which was installed in 2011.

Below is radar image at 3:19 AM on October 10th.  Precipitation intensity is shown by the colors, with red indicating very, very heavy rain.  You notice the wavy line of red colors?  THAT is a narrow cold frontal rainband---where the frontal properties are super concentrated with heavy rain, high winds, sharp wind direction changes, and extreme turbulence.  Really nasty.


By 4:38 AM, this line of intense precipitation and weather contrasts has just made landfall, with heavy precipitation just inland from the coast.


The strong upward motion with the heavy convection along the line, coupled with strong wind shear, resulted in the formation of a weak tornado, probably at EF-0 or EF-1 levels (the National Weather Service will undoubtedly send out a team to determine this).

The Langley Hill radar is a Doppler radar, so it can see rotation, and in fact, there was some indication of rotating airflow with some of the convection.  Below is a image from the wonderful Radarscope app (provided by the NWS twitter feed) for 4:38 AM.

The top image shows reflectivity at the lowest radar level, which provides a measure of the precipitation intensity.  You can see an area of heavy precipitation (reds again). 

But look at the second image that shows the velocity of the airflow towards or away from the radar.  Do you see there is an area of great color contrast between white/light red and green?  Green means air is approaching and red means going away.  That contrast of colors suggests rotation.  Weak, but suggestive.


The preliminary evaluation of my NWS colleagues (see below) is that the event was an EF-1 tornado with a peak wind of 90 mph and a path even of .5 miles.


Western WA gets 1-2 weak tornadoes a year.

And as long as we are talking about winds, we should all batten down the hatches for tomorrow.  

A relatively strong Pacific cyclone will make landfall north of us, as illustrated by sea level pressure forecast for 8 AM tomorrow morning.


The latest Seattle WindWatch forecasts for tomorrow over Seattle shows strong winds tomorrow afternoon and evening, with max gusts reaching 40 mph somewhere in the city.  We had a few trees down and power outages over the weekend-- I expect more tomorrow.

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6 comments:

  1. I have come across 3 places near me on the central Oregon coast that have a large number of blown down trees in a small area from the Labor Day winds. Not sure they were from a tornado, but the effects look similar.

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    1. A few years ago in Arlington, WA on our street there was a summer wind event of some type, i dont recall if it was clear or during a t-storm. Blew down a small maple tree ~10' tall and across the street blew over 2 ~10' flowering plum trees.
      You could surely see the path, there were 4 maples in a row, east to west and it blew only one over and the plums were five in a row north to south...the wind was a SSE to NNE flow. I think I have a photo. Pretty amazing. No damage to homes or anything else.

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  2. You have to wonder what's going on with our weather. There have been more than a few severe weather incidents on that part of the coast these past several years. A micro burst on Northshore road at Lake Quinault that brought down 100 year old trees. And several years ago the storm that flooded a wide area along the coast and stripped trees from the hills around the Quinault area. Hmmm I wonder if global warming has anything to do with these severe weather events?

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    1. Why does any weather event bring out the tired canard of "hmm, wonder if it's because of AGW?" Life doesn't contain easy answers for anyone, so stop looking for them.

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  3. I was in a thunderstorm in Gig Harbor about 7 AM today. One on Saturday afternoon disabled one of the ferries.

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  4. They didn't send out a team, but they did use my drone footage and ground images to determine a rating. I'm going to go back out this week and look for other damage as well, just out of curiosity. It was raining so hard I couldn't fly for more than a few minutes at a time, but the path was obvious. It was a very fun experience.

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