Monday, November 12, 2018

Why did the Catastrophic Camp Fire Start Where it Did?

The tragic Camp Fire of northern California has killed at least 31 people, destroyed approximately 7000 structures, and basically leveled the retirement community of Paradise, California.

It appears that the fire was initiated by a failing PG&E  power line in the Feather River Canyon just to the north of the town of Pulga (see map with arrow below).  The time of failure was roughly 6:15 AM November 8th, with fire reported 15 minutes later.


A regional terrain map shows the position of the town of Paradise (big star) and the fire initiation (red oval).


But why did the fire start in the specific location northeast of Paradise?    Even more interesting,  the regional winds were blowing, but were not THAT strong--which probably explains why PG&E did not de-energize the power lines. 

The map below shows the winds (see barbs, and max gusts over the past hour-red numbers) at 6 AM Nov. 8th, right before the power line failed.  The red oval shows the failure location (click to expand).  Sustained winds of 25 knots at the Jarbo Gap location just to the south of the failure, but mostly less.  Jarbo Gap had a gust to 51 mph, and the other locations were less.  You wouldn't think that such winds would take down big high-tension power lines.


The Jarbo Gap RAWS site is about 5.5 miles to the S-SW of the failure site, and located on a ridge.  Winds were from the northeast there, with gusts around 50 mph for several hours before the power line failed (see below).



So why did the power line fail where it did?  Could there have been much stronger winds there?  Was the location of failure one of particular vulnerability? 

I suspect the answer is yes.   To gain a big clue, lets look at the terrain immediately around the failure location.

As you can see below, the accident location was within a canyon or gap, which was oriented to the northeast--ALONG THE LARGE SCALE WIND DIRECTION-- upstream from the accident site.
Winds would tend to be channeled and strengthened in the Canyon (again the failure site shown by an oval).


But let's zoom in.  The power line failure occurred on the northeast side of a terrain feature, where the canyon narrowed.  The terrain features would have blocked the flow and thus the winds could well have been substantially accelerated at EXACTLY the location of the failure.



If I am correct in my hypothesis about the failure of the PG&E power line, it has some major implications for how PG&E decides to de-energize their lines.

They can never put in enough wind sensors to know the winds everywhere and to sense every wind hot spot.    So they may want to become much more conservative regarding when they shut down regional power lines (e.g., when winds gust above say 40 mph). 

Or they can make use of more sophisticated wind forecasting/analysis technologies, using ultra-high resolution models (e.g. grid spacing of say 50 meters) to determine where the hot spots are and how they relate to the large-scale winds.

The DRI CANSAC model, which only has 2-km grid spacing, was going for quite high winds (sustained winds of roughly 45 mph) in the vicinity of the failure site (see below) and it was not resolving the canyon properly.  So this was a real warning.  Now the model could be overdoing the winds, but PG&E folks have to understand that there can be localized accelerations in vulnerable locations, such as the one where the fire stared.

Modern weather prediction technology provides a powerful tool for making decisions about de-energizing power lines and for warning vulnerable areas.  The loss of life for events such as at Paradise can be reduced greatly with the application of this technology.

And, of course, there is something else....the rapid growth of people living at the vulnerable wildland-urban interface. 

And I won't get into the global warming aspects of this event (which I believe are quite minor).  If I talk about global warming having minor impacts, I get very threatening emails and folks try to get me kicked off the local public radio station in which I talk each week. 

Saturday, November 10, 2018

Strong Diablo/Santa Ana Wind Initiate Major Fires over Californina

It has happened again: strong, dry offshore-directed winds have initiated large wildfires over California.

Fires that have covered much of California with smoke, destroyed thousands of homes, and tragically killed nine people as of this writing.

Importantly, the winds were again highly predictable, poor warning were given to the communities, a failing electrical system may have contributed to one of the fires, and many of the people affected were living in the wildland-urban interface.

This blog will examine the meteorology of the event.

The Current Fires

There are two major fires burning right now.  First, is the Camp Fire in the foothills of the Sierra Nevada east of Chico, CA, which is burning towards the southwest and has destroyed the town of Paradise.  Nine people have died and approximately 7000 structures have been lost.  The town of Paradise is essentially gone. (see map below--acquired here).


The second major fire complex is in southern California affecting the area from Thousand Oaks to Malibu (the Hill and Woolsley Fires).  The fire has burnt to the ocean and is now moving towards Malibu.


Satellite Pictures

The satellite imagery is stunning.  Both fires started early on November 8th as offshore-directed winds surged.   The NASA MODIS satellite imagery around noon PDT shows a plume smoke heading from the Camp Fire towards the southwest, while the fires near Thousand Oaks, were just starting.


The change by noon on November 9th is amazing.  Huge smoke plumes that not only covered the entire Bay Area and adjacent locations of central/norther California, but extended many hundreds of miles offshore. The southern CA smoke plume was dense, but much smaller in size.


The air quality implications of the smoke are very serious.  The air around the Bay area was far worse than Beijing, reaching into the very unhealthy levels.  The EPA AirNow plot of particulate levels (PM2.5/PM1.0)  for Saturday morning shows that this serious health threat continues.  Unhealthy conditions are found over the densely populated Bay area and the values at some locations to the north are at very unhealthy levels.    The health implications of these smoke concentrations are very serious, leading to increased levels of asthma and respiratory problems.


The Origin of the Fires

The fires that began on November 8th were associated with strong offshore-directed winds, known as Diablo winds over central and northern CA and Santa Ana winds over southern CA.  The cause of these winds are no mystery:  an increase of high pressure over the intermountain West (e.g., Nevada) that leads to a strong offshore-directed pressure differences (pressure gradients), which in turn accelerate the winds.  The winds can be locally increased substantially by effects of of mountains (downslope wind acceleration associated with mountain wave dynamics).

To illustrate, here is the official National Weather Service chart for 7AM November 8 (Thursday). The solid lines are isobars, lines of constant pressure.  You will notice high pressure over eastern Washington/Oregon that is pushing into Nevada, and a trough of low pressure over coastal California.  Between them is a large pressure difference that accelerated the winds.


This pattern is most frequent in the fall.  High pressure over the eastern Pacific has retreated, while high pressure builds over the interior as the continent cools and the flow aloft increases.    The key "set up" is having a large ridge of high pressure aloft and a trough pushing southward into the SW US.  Exactly what we had Thursday morning (see map).


Winds gusted to 60-75 mph in "favored" locations.   The max gusts for the 24-h ending 9 AM over the region showed that near Chico there were winds gusting 72 mph in the foothills above Paradise and nearly as strong in the mountains west of Lake Tahoe (see below, click to expand).    The observational system is limited, but it was suggesting the limited extend of the strong windsto  near the crests and upper western slopes of the Sierra.


Minimum relative humidity during the same period dropped to under 10% along the Sierra foothills:



Southern California observation sites showed 50-65 mph gusts at a number of locations for the same 24-h period.


And the relative humidities were very, very low, with many stations around southern CA less than 10%:

Relative humidity of descending air is usually very low, as air warms as it descents (warm air can hold more water vapor than cold air).  Plus, the source region of the air (the intermountain west) is quite dry.

The occurrence of strong winds and low relative humdities were skillfully forecast during the previous days.  The Desert Research Institute CANSAC effort runs the WRF model at high resolution twice a day.  Here are the sustained winds predicted by their 2-km model domain for the run initialized at 4 AM on Wednesday and valid at  AM Thursday (see below).  Forecast of sustained wind around 50 mph  along the Sierra Nevada western slopes.  Gusts would be 30-50% higher typically.  Excellent warning


For southern CA, the same model showed winds accelerating at the same time (see below) to 50 mph around east and north of LA.


And then going nutty strong by 1 AM Friday.


Other weather forecast systems showed similar forecasts.  The bottom line:  the strong winds were expected and well forecast.  

These strong winds and associated low humidity were hitting a landscape dry after a summer of little rain and warm temperatures, something typical of California, with its Mediterranean climate (dry summer, wetter winters).   The landscape was modestly drier than normal around the Camp Fire, with precipitation over the past six months below normal by 3-6 inches.   Conditions around southern CA were near normal.

So the situation was highly favorable for fire.  Dry conditions at the surface, low relative humidites, and strong winds that could encourage fire growth and push the fire rapidly away from its initiation point.

And then there is fire initiation.  There is some initial evidence that the Camp Fire near Chico was the result of a failure of a high-tension power line that started the fire.    PG&E, even with very winds forecast, decided not to de-energize their line--probably a big mistake.  Just like the Wine Country fires of October 2017.  And just as disturbing, local officials did not use the Amber Alert system to warn people of the exploding Camp Fire.


The initiators of the southern California fires is still not known.

The latest surface smoke forecasts over California from the NOAA HRRR smoke system is not optimistic for today:   a LOT of smoke over the Bay area and LA (see forecast for 6 PM this evening)


Bottom Line:   Our ability to forecast these wind events has become very, very  good.   We knew how dry the conditions would be.  The threat was clear.  It is unfortunate that powerlines appears to start the Camp Fire and that the lines were not de-energized before fire was initiated.  It is doubly unfortunate that we do not seem to be able to warn people effectively when such fast-moving fires are occurring.    And the threat of so many people living at the urban-wildland interface is made clear again.

Wednesday, November 7, 2018

El Nino is Strengthening

We have known for a while that the tropical Pacific was transitioning from a neutral situation (near normal surface and subsurface temperatures in the tropical central/eastern Pacific) to an El Nino (above normal tropical ocean temperatures).  But during the past month, the warming has revved up and we will be officially in an El Nino very soon.

And we care about this, because El Ninos tend to make it warmer than normal in the NW with less snow, with the effect stronger as the sea surface temperature warms. 

Lets  start by looking at the sea surface temperatures for some "official" areas of the tropical Pacific (see below  for areas)


The Nino 3.4 area is the most popular, so lets take a look at it.  A lot of warming the past month, going from neutral conditions ( within .5C of normal) to almost 1.2C above normal.  Should be considered El Nino now.


If we look below the surface and look at the upper ocean heat anomaly (difference from normal of water temperature in the upper 300 m of the ocean) in the tropical Pacific along the equator, it is clear that ocean has become substantially warmer than normal:
Examining the sea surface temperature anomalies in map form from yesterday (below) shows the warm water along the equator and remnant of the blob in the Gulf of Alaska.  The blob is not dead yet!

The latest El Nino predictions, based on a collection of forests, projects that we will be in El Nino this winter--with more than a 70% probability.


But how strong?....that will make all the difference.  There are several types of models that predict El Nino.  Dynamical models simulate the atmospheric and  oceans using the full physics of the system.  Statistical models are based on past relationships.   Both are shown below.  Most models agree that the temperatures in the Nino 3.4 area will warm and are going for a weak to moderate El Nino.


Regarding our winter weather, the correlation of El Nino with NW weather is very weak before January 1, so anything goes for the next two months.   But if the forecasts are correct and at least a moderate El Nino is in place, expect warmer than normal winter temperatures, lower mountain snowpack than normal and a lowered probability of lowland snow after the new year.

Monday, November 5, 2018

A Stunning Video of Arizona Monsoon Thunderstorms

Rarely does one see a weather video so stunning, so poetic, with music and imagery so in sync, and that vividly communicates the beauty and grandeur of the atmosphere
.
But this week I was privileged to view such a video of southwest U.S. thunderstorms that was created by Mike Olbinski. 

The Southwest  (or North American) monsoon is associated with often spectacular thunderstorms over Arizona and the interior US Southwest during summer (roughly late June to August).   The large scale circulation pattern that produces the monsoon has high pressure over the Gulf of Mexico and moist southerly flow moving northward out of western Mexico (see graphic below produced by the Arizona cooperative extension).


 Monsoon thunderstorms are not only vigorous, often with intense and substantial rainfall, but tend to be high based, allowing a good view of rain shafts and dust storms below the main cumulonimbus cloud. 

Yes, dust storms.  Strong outflow winds can be produced by descending air from the thunderstorm that hits the surface and spreads out (see figure).  The air accelerates downward due to the downward drag of the falling precipitation and the evaporative cooling of precipitation in the dry air below.  Cool air is more dense, resulting in downward acceleration.  These winds can raise sand and dust, creating dust storms that are often called haboobs.   The strong winds moving out of thunderstorms can also be very dangerous for landing and departing aircraft.


OK, back to the video.  In it will see many examples of precipitation falling out of thunderstorms, lots of lightning, and stunning dust storms.  Click on the link below, and be prepared to be moved.  Mike Olbinski is a poet videographer.

Monsoon V (4K) from Mike Olbinski on Vimeo.

And if you like this one, there are four earlier Monsoon video and a wonderful one called vorticity.

Saturday, November 3, 2018

A Political Analysis of I-1631: The Carbon Fee Initiative

I have been disappointed in the lack of a detailed examination of the political dynamics of the I-1631 carbon initiative, with perhaps the best one being the Seattle Times analysis.   So let me try here.

I am doing this now  because I have been an active participant in the process, supporting the no side, and I don't want to seem to be gloating (if the initiative is defeated) or evincing sour grapes (if it is approved).  And in this blog I will examine whether I-1631 will pass.

The 1631 initiative race is an important one, with substantial implications regarding our ability to work together in a bipartisan way, to respect differing opinions and free speech, and in using facts, rather than ideology, to guide policy.

The Politics of I-732

Initiative 732 went before the voters in 2016, and provided a more aggressive carbon tax than 1631 but was revenue neutral, meaning that all the money was returned to WA citizens.  It was supported by a fact-driven, bi-partisan group (CarbonWa) led by economist Yoram Bauman.  I was deeply impressed by the CarbonWa folks and strongly supported this initiative.  732 had a lot going for it:  it was not regressive (its refunds made our State's  terrible tax system better) and used carbon pricing to discourage carbon use and to promote innovation.   This year, William Nordhaus received the Nobel Prize for showing the carbon taxes are the optimal way to move society to less carbon usage.

But rapidly it became clear that there were problems--not with oil companies or conservatives--but on the left side of the political spectrum.   The Alliance For Jobs and Clean Energy and its major members (such as some labor unions, Climate Solutions, and the Front and Centered group), which had a strong social action emphasis, were unhappy.   They wanted the funds from the carbon tax to be used for climate justice, green jobs, social action, and direct investments in renewable energy projects, among other things.

The Alliance tried to convince CarbonWa to drop I-732 (even though CarbonWa had all the signatures) and when CarbonWa decided to got ahead with 732, the Alliance and its left-leaning coalition members decided to either withhold support or to actively oppose I-732.  Some Alliance members also demonized the leadership of 732, saying they were insensitive to minority communities.

732 had some other issues as well.  The word tax was in its description, which was anathema to some.   And although its policy was attractive to some moderates and Republicans, it never got the support of enough voters on the right.  Although 732 was very good policy, it was perhaps difficult to understand by some (tax plus refund) and with the Democratic leadership not willing to help, it was a hard sell.

It is noteworthy how the Alliance turned away arguments of the perfect being the enemy of the good regarding 732.  And the Alliance (and the Governor) used a very phony argument to oppose 732:  that it wasn't perfectly revenue neutral (truth:  it was very close and any slight differences from neutral could have been easily adjusted by the legislature).

Without the support of some labor, most environmental groups, the Governor, and the "progressives", I-732 lost, and an extraordinary opportunity to initiate a bi-partisan effort to deal with climate change was lost.

The Legislature Takes A Swing and Strikes Out

If the legislature was doing its job, there would be no need for carbon initiatives, and last session there was an attempt to put together a package (SB 6203), pushed by State Senators Carlyle, Palumbo, and others.  It's carbon tax was lower than 732 (or 1631) and thus of limited effectiveness, had a lot (too many) exemptions, possessed advisory boards similar to 1631, and lacked a clear vision of what to do with the money.  6203 never even got out of committee, in a legislature controlled by one party.
The Return of the Coalition

As soon as 6203 failed, the group that helped defeat I-732 (the Alliance, some labor, Indian tribes and others) were ready--they unveiled I-1631, a carbon FEE initiative, in which the acquired funds (over 2 billion in the first five years) would be used for a variety of  unspecified climate justice, renewable energy, jobs, and adaptation programs.  The core of the I-1631 alliance approach, why they rejected 732, was their wish to access billions of dollars of carbon fee/tax dollars. And 1631, if passed, would give them that access.

But the 1631 group had a problem  There is substantial documentation that climate change is WAY down folks list of important issues, and that few are ready to make any kind of financial or personal sacrifice to reduce carbon in the atmosphere.   Even climate researchers are unwilling to reduce their carbon-emitting travel. I hate to admit it, but my climate research colleagues have the worst carbon emission profiles of anyone I know.

The I-1631 organizers knew that climate change would be a loser in an initiative, so they transformed the initiative into an effort for clean energy, clean water, clean air, healthy communities and jobs!  Who could be against that?  Global warming? Climate change?  Not much talk about that.

Climate change was something the 1631 crowd generally avoids talking about.  Because even if I-1631 met its goals (reducing carbon "pollution" by 20 millions tons annually by 2035), global temperatures would only be lowered by about a thousandth of a degree.

The 1631 leadership decided to spread around the carbon fee money to their coalition, first by creating a supervisory board in which they would have a lot of representation and control, and second, by hardwiring money to parts of their coalition (Indian tribes, labor, social action groups).

So 1631 was designed to be attractive:  a very low carbon tax, while spreading around a lot of goodies to the members of the supporting coalition.   And it even advertised that someone else would pay--the big, bad oil companies.

And an important issue was that this "largest coalition ever" had virtually no representation from Republican and conservative groups, and thus 1631 was highly partisan.  It would never serve as a model for the rest of the nation.

A Lucky Break for I-1631:  Wildfires and Hurricanes

And then the 1631 folks got lucky.   Wildfires return to British Columbia, eastern WA, Oregon, and California, with substantial smoke over Washington.  The fact that a century of wildfire suppression and poor forest management was key for generating the big fires, and the fact that fires are a natural part of the regional environment was ignored, as was the fact that a lot of smoke came from BC, where a carbon tax is in place.  Research showing that climate change is only a small contributor at most of our recent fires was ignored as well. 

The 1631 crowd realized that they could use the wildfires as a powerful marketing tool, making all kinds of claims that I-1631 would stop the fires and smoke (see below).  The truth is different, of


course.  Global warming is not a major contributor to our local fires and the initiative does not commit the huge sums of money needed to restore our east-side forecasts (thinning, removing debris, prescribe burns). As the saying goes: truth is the first casualty of war....that appears to be true of initiative as well.

However, the smoke had a huge psychological effect on the region and the 1631 crowd was ready to milk it for what they could.  And 1631 missives/tweets/message suggested that Hurricanes Florence and Michael resulted from global warming (not true, GW only increased them by a few percent) and made use of hurricanes in their imagery.   Truth again a casualty.


The Political Calculus:  The Elway Poll

In early October, the Elway polling organization took a sample of roughly 500 WA state registered voters, and a question about I-1631 was included.   This poll suggested that 50% were in favor, 36% were against, with 14% undecided.    A good sign for the initiative?  Maybe not.   Elway himself stated that the undecideds in initiatives tend to drift towards the no side.  More importantly, in his experience few initiatives pass that start out with 50% or lower early in the season.

But there is something else:   the question used was flawed.  The first line is "This measure would impose pollution fees on certain large emitters of greenhouse gas pollutants starting in 2020."
Notice it states that "large emitters" would pay.  It says nothing about folks themselves paying.  People tend to be happy if someone else pays for all the goodies.  Even with someone else paying, only 50% supported the initiative.


The implication of this wording is enormous. Folks don't want to spend real money on climate change or make any real sacrifices.  With only 50% answering yes above, and assuming the Elway poll was accurate, all the NO side had to do is to deliver the message that people would have to pay themselves and the initiative would lose.  And that is exactly the message the NO side is stressing.

The Trump Effect

Even with substantial flaws, I-1631 has a big positive going for it:  the intense anti-Trump/anti-Republican sentiments of the Democratic left.  The latter group is looking for ways to push back against Republicans, to prove their power to change the agenda.  Thus, many Democrats are willing to overlook the flaws and lack of bipartisanship of 1631 and push it through.  This viewpoint is particularly strong among young left-leaning voters, many of which are energetically working for 1631.

The Divide Between Segments of the Democratic Party

There is an interesting divide between "progressive" well-to-do elements and the working-class portion of the Democratic party.   The progressive folks, and some of their "climate justice" allies destined to benefit from 1631, strongly support 1631, but working folks, including much of labor, are uncomfortable with it and suspect (rightly I believe) that they will pay the bills.  I suspect that a lot of the working folks will vote against 1631, but we will know on Tuesday.  The combination of working class Democrats and Republicans, may be enough to stop the initiative.

Going Negative and Being Untruthful

The Yes on 1631 campaign is in a bind.  The initiative itself is poorly written, hyperpartisan, will do little to slow global warming (.0001 degrees C!) and most folks understand the oversight board will not use the money wisely.  So the Yes campaign has gone super negative in the public statements against the No campaign and its supporters.

Headlines and mailers proclaim that the oil companies are lying!  Virtually every one of their mailers talk about lying oil companies.  But the Yes folks never reveal what the oil companies are lying about.  The reason is that the oil companies are generally telling the truth in their messages. The Yes folks are lying about lying.


In contrast, the deceptions of the Yes side ares so extensive, it would take a blog just to list them all.  That people will not have to pay--oil companies will cover the tab!  That the wildfires are mainly the result of greenhouse gases and global warming, and 1631 will make the smoke go away.  That the initiative is about clean air and clean water, rather than dealing with greenhouse warming. 

Perhaps the most recent and toxic lies are the accusations that the No side is using fake endorsements for hispanic folks.  The truth is that there are signed endorsement sheets for everyone listed.  Is it possible that some storeowners or individuals signed stuff without a proper reading?  Of course.  But to accuse the No leadership of deliberate deception is contrary to the facts and it appears that the Yes group is putting enormous pressure on No supporters to change their endorsement.

The No Side Has Not Been Effective

I really think the No side has not done a very good job in making their case.   The oil companies accept the threat and reality of climate change.  They should make this better known.  Several oil companies would support a reasonable national carbon tax.  That should be advertised.   A more positive proactive stand on climate change would have quickly evaporated support for the initiative among many. And they are spending too much money, with too much advertising, that makes their funding an issue. 


Will the Initiative Pass?

In a normal year, the answer would be no.  People are not willing to sacrifice or spend money to stop climate change.  They certainly would not sacrifice without clear deliverables.  People are suspicious of an unelected board making billion-dollar decisions.  Working class Democrats are not favorably inclined.  All the no campaign had to do was to clarify that individuals would have a substantial cost and it would be over.  The Elway poll suggests to me that the initiative will fail.

But the "blue wave" and resentment against Trump among the Democratic 60% of the state might be enough to push through 1631, even with all its flaws.   And there is another question: might all the media coverage of climate change (much of it exaggerated and non-factual) have finally motivated people to vote for a measure that would require some sacrifice?  We will find out on Tuesday.

A Heavy Responsibility

If 1631 is defeated, the Yes on 1631/Alliance group will bear a very heavy responsibility.   They undermined I-732 two years ago, leading to its defeat.  Then they came up with the problematic 1631, excluding moderates and Republicans in the coalition and following an approach that was problematic for the working class part of the Democratic coalition.

Thus, they would be responsible for two failed attempts in dealing with climate change in Washington State.  A waste of nearly 50 millions dollars for the two campaigns.

 I suspect many 1631 leaders know that 1631 has a good chance of failing, and are setting up the excuse:  the big money from the oil companies, rather then their defective initiative.    If it fails, perhaps a message will finally be clearly delivered:  only a rational, bipartisan approach has a chance of moving forward.

Thursday, November 1, 2018

Aloha Winds Over Puget Sound

If you walk outside and close your eyes, you might imagine your were in Hawaii, with strong trade winds bringing in pleasantly warm air. 

This evening, many western Washington stations are around 60F with a persistent breeze of 10-15 mph and some higher gusts.

And strangely enough it is basically dry near Puget Sound, while heavy rains are falling in the foothills.

You doubt the Hawaiian connection?  Let me show you.

Here is a wonderful image from a weather satellite that measures the amount of moisture in a vertical column of air (taken earlier today).  Lots of water vapor in the tropics (red and purple colors) because the warm air can hold a lot of water vapor.  But look closely--do you notice a tendril of higher water vapor heading towards the Northwest?

 Here is a blow-up of the relevant section.  That narrow current of large amounts of water vapor is an atmospheric river and you will notice that it starts around Hawaii.    That is why such atmospheric rivers are called Pineapple Expresses.


But we can have more fun....we can use our model output to run back-trajectories, which shows us where the air over us now came from.   I did this using the very nice NOAA Hysplit system, showing trajectories ending at 100 meters, 3000 meters, and 5000 meters above SeaTac Airport. You can see the air at these lower levels is coming from the region northeast of Hawaii.


With this origin, the air is relatively warm, with lots of water vapor.

But why is Seattle dry while the Cascades foothills are getting inundated (as demonstrated by the precipitation over the past 24h shown below, click to expand)?


Because the winds approaching the region are westerly, with Puget Sound being in the rainshadow of the Olympics.

And yes, one more question.  Why are we so windy tonight, with gusts to 25-40 mph at some locations?  To illustrate, look at the winds at West Point in Seattle.  Winds are gusting up to nearly 40 knots and still increasing!

The explanation:  A low center is passing through BC to our north, resulting in a large pressure gradient (difference)  over western WA (see map).  The large N-S pressure gradient is producing quite strong southerly winds.


eʻoliʻoli i ke aniau o ke ao