Saturday, December 15, 2018

Heat Wave Hits Port Angeles While Strong Winds Battered the Region

The first good blow went through the region on Friday, bringing localized gusts of 40-50 mph and the loss of power to around 100,000 customers in western Washington.

Branches always fly during the first storm of the winter and even a few trees were lost.  Forecasts were decent.

But the most interesting aspect of the storm was not the general power outages and wind gusts, but the strong downslope winds and AMAZING  and sudden jump of approximately 20F around Port Angeles, on the northern Olympic Peninsula. 
Lots of power outages occurred in Seattle yesterday with the strong winds.

Here is the  observed temperature plot at Port Angeles during the past few days (time in  UTC/GMT and increases to the right).  Yesterday, the temperatures surged by 20F over roughly 2 hours, from around 46F to 65F, stayed there a few hours and then dropped to around 40 F over a few-hour period.   Talk about extreme temperature changes!


Mama MIA!  What was happening there?

The answer:  a strong mountain wave circulation forced by the interaction of increasing southerly (from the south) flow and the Olympic Mountain range.  This resulted in strong downslope flow descending into the Port Angeles area.  The air  warms rapidly as it sinks due to something known as "adiabatic compression" resulting in the brief heat wave.

Let's take a closer look at the conditions at Port Angeles during the crazy heat wave.  The plot below
shows the sustained winds (blue lines), gusts (red lines) and sea level pressure (green lines) over the same period.  There were two events (low centers) that occurred during the period shown, with the second (Friday's) being the stronger one.   Winds surged to around 40-45 kts, just as the temperatures surge.   A separate plot (now shown) indicates that the strong winds were from the south, thus descending down the steep northern slopes of the Olympic mountains. 


And look at pressure (green line)--a period of very low pressure occurred when the temperatures surged....keep this in mind, it will be important.

A plot of the temperature, wind gusts (red numbers), wind barbs, and dew point (blue numbers) show the conditions around 2 PM Friday.  Strong southerly winds reached Port Angeles (gusts to 45 knots) and you can see the localized warm temperatures (click on plot to expand).


The winds were strong enough to down trees and cause extensive power outages on the north side of the Olympic Peninsula.

So why was there strong northerly winds descending down the Olympics into the Port Angeles area?

A large-scale low pressure trough was approaching the Washington coast, increasingly southerly winds reaching the Olympic mountains.  The air pushed against mountains and a mountain wave developed over and downstream of the mountain crest.   As the air rose, it cooled as it expanded, with the cooling causing the air to become more dense, resulting high pressure on the windward (southern) side of the Olympics

Subsequently, as the air sank on the northern side of the Olympics, it was compressed and warmed.  Since warm air is less dense, an area of low pressure (or a pressure trough) developed over the northern slopes of the Olympics.  To illustrate this situation , here is a simulation of the sea level pressure (solid lines) and wind speed (shading) for 10 AM on Friday.  You  can see the high pressure/low pressure couplet and the large pressure difference between them.  That pressure difference accelerated winds to the north and down into Port Angeles.


The flow configuration is called a mountain wave, because of the wave-like up and down of the airflow, something illustrated by a SW-NE vertical cross section across the Olympics at 10 AM Friday.  The air flow is roughly parallel to the solid lines (potential temperature) ....you see the wave-like structure?  The shading show clouds-- plenty of them on the SW side of the mountain, but none in the descending air to the NE.



And as noted above, the descending air rapidly warms, creating the warmth on the north side of the Olympics.    The high temperatures recorded in the region yesterday show the extent of the warmth, with the highest temps around Port Angeles (click to enlarge).


Clearly, the incoming flow was just right for the development of strong northerly flow  and warmth on the north side of Olympics.  But unfortunately, our friends  around Port Angeles will have to  accept  the fact that they won''t always have Los Angeles weather in December.

10 comments:

MAC in Bellingham said...

Thank you for the post-mortem. Waiting this morning to see if today's wind advisory will materialize. Nothing much so far. A few comments:

1. You indicate this was a decent forecast. What constitutes a good public weather forecast seems like a somewhat complicated question as it involves a number of factors, like risk of harm. But it seems it missed quite a bit in terms of where the most damaging winds occurred. I would be interested in knowing how closely your forecast models predicated the actual path, intensity, and timing of the event.

2. In terms of what happened in Port Angeles, that really was not part of the forecast at all. It seems like it was a very local event. At first glance, it is a little to understand why it had so much impact. The winds were pretty short duration and not all that strong. A few gusts of 45 mph and relatively low continuous winds is not at all uncommon in that area. You could argue that the winds they had a few days earlier on December 11 and 12 were more substantial even if the few gusts were not as strong. My best guess is the area usually receives strong winds from the west and sometimes from the east, but not usually from the south. So, perhaps, a lot of trees and limbs were more vulnerable to winds from a southerly direction. In addition, I do not know if trees still had an unusually large number of leaves for this time of year.

3. We had a similar temperature change in Bellingham as Port Angeles (63F @ 7:35am, 49F @ 8:53am), but not as dramatic. But it was definitely strangely balmy in early morning. I incorrectly thought the drop was caused by the passage of a front, but that did not square with barometric changes or satellite pictures. So, I have been puzzled what caused it here. After reading your analysis, I thought perhaps it was caused by winds from the Port Angeles area bringing warm air to Bellingham or maybe downslope winds from cascades.

MAC in Bellingham said...

It looks like the worst of the Clallum county outages were caused by issues with BPA transmission line and open breaker problems, which resulted in the entire county to be down at 2:36pm on the day of the storm:

https://www.clallampud.net/weather-related-outages-occurring-county-wide/



gnolan said...

Classical thermodynamics was one of my favorite topics in physical chemistry (later in geology as well) so I find it cool to see the application here. Will need to re-read to absorb details.

Chris H. said...

Just read an article by Alex Lenferna, an educated fellow who deals in ethics as a student philospher. He also was highly involved in promoting I-1631.

Mr. Lenferna's article was focused on Cliff Mass's opposition to I-1631.


AlexLenferna/if-you-care-about-climate-change-dont-listen-to-cliff-mass-vote-yes-on-1631-d61b2631226b


What struck me as odd was this highly educated man reverted to the worst kind of ad hominem attacks on Cliff to make his point on why Cliff was wrong and should not be listened to.

"Cliff’s theory of change is like that of a spoiled toddler."

This ethical teacher also built several straw man versions of Cliff and argued against those, going so far as to imply Cliff is a racist because of a picture Cliff posted of pigs feeding at a trough.

Instead of interpreting this Photograph as an example of I 1631 being pork barrel politics, the ethics teacher chose to interpret the photo to better serve his Personal Agenda.

"Cliff compares tribal nations, communities of color, and laborers to pigs for asking for investments in their communities. It’s a disturbing, callous and arguably racist analogy"

I have to ask, should a man of Ethical study engage in personal attacks and logical fallacies as a foundation for debate?

Mr. Lenferna, you seem like a well-traveled fella who accuses others of being in bed with big oil.

You also seem like a world Traveler, you know cause you most likely flew here from your home land and I'm guessing you visit there on occasion.

How often do you fly by the way? How large is your own personal carbon footprint?

You do realize that by getting on a jet aircraft that immediately and completely places you in bed with big oil?

Think a carbon tax or carbon offsets are going to reduce the carbon footprints of the wealthy?

An educated man should recognize his own biassed arguments for what they are, an irrational attempt to justify a healthy serving of pork.


We are a rich Nation that can use our current monetary resources to move towards a renewable energy and conservation strategy. We don't need to tax the poor and then hand them weatherstripping to get there.

Forecast high for this Wednesday is 41° in Twisp Washington.

Chris H
Heli-free North Cascades







meetsy said...

MAC in Bellingham... we didn't have a short blast of wind, as you assumed. The wind started about 4-5am, and blew continuously, in huge waves, and in long and short bursts for almost 12 hours. I've lived here for 20+ years, and the wind storm 12 years ago (similar in the making) only lasted for a couple of hours.

This wind storm wouldn't have been as bad IF it had been shorter in duration, or if it wasn't swirling. There were clearly "mini-tornado" winds that whipped around the trees. You could see them...where winds were blowing some trees in a stand in one direction, while the others were whipping in the other direction, which is how we lost a lot of branches, and tops of trees.

Nearly 12 hours was insane.

Gregulator said...

Yes Mac, we do usually get our big winds from the west (and occasionally east). However it's usually strongest near the water and getting weaker as you go inland. On days it might be blowing 20 knots near the shoreline it will be much calmer only a few blocks inland, between the bluffs and all the trees. Even big storms with 25 knot sustained gusting over 30 knots at the airport or coast guard station don't see anything in town like we saw on Friday. The big winds were right where all the houses are, in addition to being from an unusual direction. The wind was incredible, with quite a bit of damage to fences and shingled rooves.

And it wasn't forecast - I regularly read the civilian and aviation forecasts as well as the NWS discussion. There was a lot of talk about the big wind coming in the afternoon with the cold front passage, but no real warning of those downslope winds in the morning, from the south. (Not that there's anything you can really do to prepare your roof, anyway)

MAC in Bellingham said...

meetsy said...

"MAC in Bellingham... we didn't have a short blast of wind, as you assumed * * * Nearly 12 hours was insane."

Sounds terrible and you have provided a good description of why there was this much damage. The PA weather stations don't really capture this, but I see that the airport data stops at around 8 am, which I guess is when the power went out:

https://www.wrh.noaa.gov/mesowest/timeseries.php?sid=KCLM&num=168&banner=gmap&raw=0&w=325

I have been through about 8 pretty good wind events, the worst of which was the 1962 Columbus Day storm in Portland when I was a teenager. Windstorms have a way of creating a strong feeling of helplessness, particular if it is night and the power has gone out.

Subjectively, it feels like we are getting November weather about 6 weeks late this year. After nothing much happened in November this year, I wrongly thought we were home free. The NWS did a better job of yesterday's wind prediction in Bellingham. Winds were stronger and more sustained compared to December 14 as reported at the airport. NWS missed somewhat on timing, however.

MikeH said...

I suppose it all depended on where you were. I just got power (and news) back after losing it last Friday. The winds here- 10 miles west of PA and at about 1000 ft elevation - were chaotic. A lot of timber went down just uphill of me and utility poles broke in many places. This was not a 45 mph event. As an old timber cruiser- I'm quite familiar with the usual lee slope effects of high winds on forest stands and this was not that. It was patchy, you got both east and west winds within moments and much of it was swirling. Sort of like what happens when you pour water straight down and it hits the ground. Lots of radial splash.

So glad we didn't get snow as well.
Love the blog and keep it up!

Ian Barclay said...

I have lived in Sequim over 10 years and this storm was like nothing I have ever seen. I've been over to Port Angeles twice since Friday and it is a mess. The sides of 18th St. are still littered with an accumulation of douglas fir branches at least 1' deep. Trees were down all around town (many are already cleaned up, of course); I'm amazed more trees didn't fall on houses. In some neighborhoods every other residence lost at least one tree. Lots of roof shingles were lost and I have several friends whose trampolines went airborne causing some destruction.

I observed that blowdown of trees and fences was mostly to the NW, N or NE indicative of winds from the opposite directions... but also a few fell to the south. Likewise, at our place in Sequim, we didn't get as much wind but we still had one insane gust that was out of due north which knocked over a tree and pushed our trampoline across the yard.

So I know a windstorm was forecast but it no one thought it would be this exceptional. This is definitely the worst wind damage to hit Port Angeles in a long time, which was NOT expected. Usually if anything the NE Olympic Peninsula is somewhat sheltered from stronger winds during typical storms. As far as I can tell what was missed in the forecast was the mountain wave factor. And there is no accounting for the occasional, strong northerly gust if not rotating "cylinders" of air under the waves (which Cliff discussed in an earlier post).

As a responder above put it "insane" pretty well sums it up. I grew up in the Northwest (not the Sequim area) and have lived through all our windstorms... but this was intense!

meetsy said...

Mac,
I was raised in Northern Nevada.... and the Washoe Zephyr were a big part of my childhood. They happen regularly (with less velocity) in late summer, but the autumn ones are the worst. The worst always seemed to hit just as tumbleweeds have dried out and are ready to break off.

The weather reports would say things like "if your child is under 70lbs, please keep them indoors".

There can be sustained winds of 60mph, and gusts of 90 (although the strongest I remember was in the late 60's, and it was counted as 120mph before the weather device broke off). These winds don't just blow once and stop, they blow daily (often) for several days at a time -- some days stronger, some days weaker).

I have clear memories -- as a small kid -- being stuck on the cyclone fence unable to get back to my classroom at recess. Waiting...just waiting for the teachers to come and gather the kids and herd them back to the school. The worst thing ever is stuck on the fence, watching the giant prickly, scratchy tumbleweeds barreling right towards you.

Wind scares me, so I pay attention to it.