Thursday, April 26, 2018

Is "Weather Whiplash" Increasing In California?

This week a paper was released in Nature Climate Change by Daniel Swain and co-authors that made a bold claim:  that California is experiencing and will increasingly experience "weather whiplash" because of anthropogenic global warming. 

They define "weather whiplash" or "precipitation whiplash" as a transition from a much drier than normal year to a much wetter than normal year, such as the change that occurred between the winters of 2015-2016 and 2016-2017.


As one might expect, with such an explosive claim and graphic metaphor, the media would go wild over it.  They did.  Headlines describing the civilization-testing whiplash were found in media outlets across the world, from the front page of the LA Times to CNN and even made Dan Rather's blog.  Environmental activists website covered this revelation in depth.


But I suspect most reporters did not read the paper, and as I will describe below, this work suffers from substantial problems and claims that are at the best excessive, even using the model simulations they describe.  And the results are entirely based on model results that don't seem to match well with what has happened in the real world.

The Claims

Swain et al.'s claims of a precipitation whiplash is based only on climate model output and so is only as good as the model.  Specifically, they used a 40-member collection of forecasts (an ensemble) using the Community Earth System Model (CESM). This is a global model developed at the National Center for Atmospheric Research. I am quite familiar with CESM and have used its output in some of my own work.  It is run at approximately 1° horizontal resolution (about 111 km) and thus is unable to simulate the details of western U.S. precipitation and weather systems.

The definition of whiplash used in this paper is a bit arcane and one-sided.
Specifically, they only considered a whiplash from dry to wet conditions.  For some reason they did not think a wet to dry whiplash was important. 

Swain and colleagues looked at the distribution of precipitation in the model during a pre-industrial period (before 1850) and found the top 20% and bottom 20% precipitation years.  With those numbers they examined CESM climate simulations, encompassing most of the 20th and 21st centuries, that was driven by an aggressive (probably too aggressive) increase of greenhouse gases (RCP 8.5 in climate modeler lingo), looking for the frequency  of changes from dry (the bottom 20% before 1850) to wet (top 20% before 1850) years.  And they did this for each ensemble member and thus was able to get the change in frequencies of this one-sided whiplash as the model simulations forced by increasing greenhouse gases.

Their results are found in the figure below for some model grid boxes in southern and northern CA (they don't really specify in the paper exactly where), showing the change in frequency of dry to wet precipitation whiplash events.  A measure of the range of climate model whiplashes are shown by the purple shading (67% of the simulations are within the shaded areas and purple line shows the ensemble mean (which has been smoothed or averaged over time)).


So, what does their analysis of the models show? 

For northern California, not much.  A decline in whiplash in the 1970s, an increase from roughly 2015 to 2025, and not much change for the next 30 years.  According to their own analysis, the changes in northern CA are NOT statistically significant.  And keep in mind that most of California's reservoir capacity is in the north.

For southern CA, there is an abrupt change from reducing whiplash to a very slow steady rise starting around 1985, with the whiplash remaining quite small until mid-century.  Considering that the envelope of uncertainty encompasses zero change until around 2050, I am sure the change would NOT be statistically significant through that time.   As shown later, this evolution in southern CA does NOT compare well with observations through 2018, where there is no trend.  And in any case, southern CA has few large reservoirs and only a small amount of California agriculture.


In general, there paper shows not much change in the number of dry years but increasing wet years for the northern two thirds of the state as we proceed into the second half of the century.

What has Actually Occurred with Precipitation Whiplashes

Here is the average wet-season (November-March) precipitation for California from 1936-2018 from the NOAA/NWS Division data available from the wonderful NOAA ESRL website.   This plot and subsequent plots were made by UW Atmospheric Sciences staff member, Neal Johnson.  Why did we start in 1936?  Because the ESRL website said there were issues before 1935.

Not much trend in CA precipitation, but plenty of ups and downs---now known as whiplash, I guess.


Anyway, since this is science, let's create a WHIPLASH INDEX (WI) that is simply difference between one year's precipitation and that of the year before (shown below).  (Note, the correct pronunciation of WI is "why").   Now this is a bit different than Swain et al. whiplash plot (they showed the frequency of increases of precipitation between very dry years (bottom 20%) and wet years (top 20%).  But my index is much easier to understand and is more informative.  And my index is based on OBSERVATIONS in the REAL WORLD unlike the model-based whiplash guidance in the Swain et al. paper.

What is clearly apparent is that it is hard to find evidence of an increase in amplitude in the whiplash index based on observations.   Now, if we look at the trend of increases in precipitation (above the dashed line)--which is very similar to Swain et al's approach-- there is no evidence of increasing dry to wet years.  In fact, there are LESS of them during the past two decades...and more in the decades before.

Or look at the wet to dry transitions---no evidence of any trend.

But let's take this one step further, Swain et al. divided their whiplashes into southern and northern California.  Let's do better than that (a UW Husky will always try to improve upon a UCLA Bruin)--- let's calculate the whiplash index for southern, central, and northern California (below).

Northern CA


Central CA
Southern CA

These results are very important--they show there is NO increase in precipitation whiplash for any sub-region of California WHEN ONE LOOKS AT WHAT ACTUALLY HAPPENED.

In contrast, the model output applied in Swain et al shows that there is an increase in whiplash events starting around 1985 in southern CA and 2005 in northern CA.  The clear conclusion is that something is amiss with the model in predicting California precipitation.   And therefore, the predictions  used in this paper are suspect.

The fact that the model is not getting the year by year variability correct for California precipitation is hardly surprising.  West Coast precipitation is modulated by El Nino/La Nina and teleconnections (remote physical connections) forced by convection in the tropics.  And such low-resolution models do a poor job on tropical convection and thus will mess up the teleconnections.  I know a lot about this because I am actively working in this area.  And there is a way to fix the problem...but it takes huge computer resources.

But even if their model output was correct, I would argue that they and certainly the media are way overhyping these results.     In fact, at face value their predictions are good news for California.  According to their results, the increase of whiplash events in northern California is slight and is not significantly significant at even the low 90% significant level (more studies use 95% significance).  And most of the reservoir capacity in California is in the northern portion of the state.

They also show that there will be an increase in winter precipitation over time across most of California.   Now California (unlike Washington) has huge multi-year storage capacity, so even if their model is right and there was more year to year variability, California would be fine....they simply will store the water from the wet years.



There are a lot of other technical issues with the paper I could bring up, but the bottom line is clear:

(1) observations over the past 80 years do not show an increase in precipitation whiplash in California even though the effects of global warming have begun.
(2)  their model results are inconsistent with observed trends
(3)  even if they are right, the implications are positive, not negative.  California will have more water over time.

Now it is true that temperatures will increase and that will cause more evaporation and drying.  Sierra snowpack will decline (but the water will still be there as rain).  So California will probably want to add more reservoir capacity and waste less water (more drip irrigation, less crazy water loving crops).  They could even push water underground during wet years.  This is a solvable problem and not a existential threat. Weather whiplash will probably be the least of their problems.

This "whiplash" frenzy in the media shows a major failure mode in our conversations about global warming.  Some researchers analyze purely model results.  They don't compare the model output with observations.  They find some modest changes in the model projections and somewhat inflate the importance in their paper.  The media and certain interest groups hype up the results with big headlines.

As a result, the public is exposed to essentially incorrect information and gets turned off by another apocalyptic prediction.  And such poor communication gets in the way of properly dealing with climate change, a serious issue, in a rational, fact-based way.

Tuesday, April 24, 2018

The Subtleties of Warmth

For many in western Washington and Oregon, today was the warmest day of the past seven months... this was true at Sea-Tac Airport, where temperatures rose to 77F this afternoon (see plot of temperatures since 30 September...today was the warmest).
The plot of high temperatures today (Tuesday) shows some interesting contrasts:  mid-50s near the water.  70s over land around Puget Sound, and 80s near the coast and in the warm Willamette Valley.



Why so warm along the coast?  Because there was strong easterly flow aloft.  This is shown by a plot of winds over time above Sea-Tac Airport (red are temperatures, blue are wind barbs, time is in UTC/GMT with 24/18 indicating 11 AM this morning, the y-axis is height in pressure with 850 being about 5000 ft)  Strong easterly flow developed in the lower atmosphere last night and this morning.
Easterly flow pushes the cool marine influence offshore and produces downslope warming on the west side of terrain (like the Cascades and coastal mountains).  The coast enjoys the downslope warming benefits of two mountain barriers and thus gets very warm.

Another interesting oddity is the minimum temperatures this morning.  72F near Black Diamond in the eastern foothills of the Cascades and 60s nearby.  Why so warm?  Because of downslope warming off of nearby terrain!


 Tomorrow will be warm, but not as warm as today.  Why?   Because the easterly flow has weakened and remain weaker on Wednesday.  The sea level pressure forecast for 2 PM tomorrow shows a thermal trough of low pressure extending into southwest Washington and less east-west pressure difference than today.  Such a pattern tends to give us more northerly than easterly flow over the Sound...thus, a cooler pattern.

Thursday at the same time, the trough has pushed northward to Bellingham and the flow is more easterly over the Cascades--thus I expect warmer conditions (upper 70s that afternoon around Seattle).  But the end of warmth will be upon us soon.   With the approach of a low offshore, a ridge of high pressure builds along the coast and a strong coastal pressure gradient is building.


The result will be an onshore push of marine air late Thursday/early Friday, with considerable cooling on Friday.

So enjoy the next two days....precipitation and cooler temperatures are in store for the weekend.
_______________________________________

Announcement:  The Northwest Weather Workshop is on April 27-28
LAST DAY TO REGISTER
The NW Weather Workshop is the big annual meeting for those interested in Northwest meteorology.  This year we will have a major session on the meteorology of NW wildfires and others on other aspects of our regional weather.  The gathering takes place at the NOAA facility in Seattle.  To view the agenda and to register, go to the meeting website.  The workshop is open to everyone, but registration is required.


Sunday, April 22, 2018

The Upcoming Heat Wave in the Pacific Northwest

During most years there is what I call a mid-spring heat wave, typically between mid-April through mid-May.

And we are going enjoy such a heat wave this week.  But why a mid-spring heat wave?

By mid-April, our sun is strong and the days are long....keep in mind that the sun's strength today is the same as August 20th.


But to get the heat we have to turn off our natural air conditioning...onshore flow off the cool Pacific.  And to get real warmth, some nice downslope flow down the western slopes of the Cascades, allowing air to warm by compression.

And there is a way to do this...have high pressure build to the east of the Cascades....and that is exactly what will happen this week.

The fact we often get heat waves in April and May is obvious by looking at a climatological plot of extreme daily temperatures at Sea-Tac Airport (yellow line below).  Temperatures have zoomed up to 80 in April, 80s (even low 90s) during May.


At the UW we run a high-resolution ensemble of 15 forecasts to get a handle on the uncertainties in the forecast.    Here is prediction for surface air temperature from last night's run.  The black is the ensemble average...normally a very good forecast.   Nearly right-on for today (high got to 59F).  Tomorrow's model forecast bringa Sea-Tac to 70F...roughly a ten-degree hike.  And 75F on Tuesday.

Want more assurance of the warmth?  Here is the latest output of the National Weather Service Short-Range Ensemble System (SREF). 70F tomorrow, 75F on Tuesday and a bit warmer on Wednesday, although you will notice that there is increasing uncertainty (the forecasts vary more).


 You really want to enjoy the warmth before it happens?  Let me show you the surface temperature forecast maps from the UW system.

First, the forecast for 5 PM tomorrow (Monday).  68-72F in much of western Washington.  72-76F around Portland and over the western foothills of the Cascades.


Tuesday at 5 PM.  Amazing. Upper 70s from Seattle to Portland.  Even along the coast, thanks to the offshore flow.


Wednesday at 5 PM.  A bit cooler over Seattle, but much warmer around the Columbia Basin of eastern Washington.  This is a sign that the high pressure is moving eastward.


Enjoy the warmth...after a cool, wet few weeks it will be nice to experience the spring-time lushness of the Northwest under sunny skies and perfect temperatures. 

There is one problem, though....the pollen count is high right now and according to pollen.com will get higher with all this warmth (see below).   Sorry...




Saturday, April 21, 2018

The Connection Between Heavy Rainfall in Kauai and Washington State Last Weekend

Last weekend brought catastrophic rain to Kauai, resulting in floods and landslides.  And last Saturday, portions of Washington State were inundated with heavy rain that brought localized flooding.

The interesting thing:  they were directly connected.  Let me explain.


Kauai by any measure is a wet place. But it is also a place of great precipitation contrasts. These contrasts are directly related to the terrain, with the two highest peaks being Kawaikini (5243 ft) and Mt. Waialeale (about 5150 ft.).   Moist tropical air ascending this terrain results in huge amounts of precipitation.


The annual precipitation illustrates this (below), with much of the higher terrain soaked by over 150 inches a year. In fact, the heaviest average annual precipitation in the U.S. occurs at Mt. Waialeale with 460 inches a year-- much more than our Olympics, which enjoy the record for the highest total in the rest of the U.S. (about 150-180 inches a year on the windward slopes).  The northern/northeastern side of Hawaii tends to have heavy precipitation since it faces the incoming trade winds, while the southeastern side (e.g, Poipu) is relatively arid, with only 20-40 inches a year.  Most vacationers head to the south side of the island for obvious reasons.


Last weekend there were unimaginable amounts of precipitation hitting Kauai. Below are the 48-h totals for the 48-hour period ending at 6 PM HST on April 15, 2018 provided by the National Weather Service. All values are in inches.
Wainiha and Hanalei on the north side got huge amounts (28-32 inches). No wonder there was massive flooding. But Kalaheo on the southern side only had 1.55 inches (which is still a significant amount of rain)

Wainiha : 32.35 
Hanalei : 28.41 
Mount Waialeale : 22.34 
Princeville Airport : 14.60 
Kilohana : 13.19 
North Wailua Ditch : 10.62 
Kapahi : 10.12 
Wailua : 8.21 
Lihue Variety Station : 3.36 
Anahola : 3.20 
 Lihue Airport : 1.92 
 Kalaheo : 1.55 

A map of the 24h amount ending 9 AM HST April 15th shows the amazing contrasts.  Keep this in mind when you consider a vacation in Kauai.


Back to the connection with Washington precipitation on Saturday.   As noted in an earlier blog, an atmospheric river brought heavy precipitation to our area that day, with up to 2 inches in Seattle and 3-6 inches in the mountains.

It turns out that there was a direct connection between the plume of moisture hitting Washington State and the moisture inundating Kauai.   The UW model forecast for the vertical total of precipitation at 5 AM Saturday (PDT) shows this.


And a satellite-based measurement of moisture for the 12h ending 5 AM (PDT) Saturday, shows the connection, with Kauai getting hit by MUCH larger values (orange colors) than we endured.
 And the connection was quite clear in satellite-based water vapor imagery, with the lighter colors indicating more water vapor in the upper troposphere.


But what caused the connection in moisture?  An upper-level (500 hPa) map at 5 PM Friday (0000 UTC 14 April) shows an extensive upper level trough that extended back to Hawaii.  The strong southwesterly flow associated with the trough (where the lines are close together) moved moisture into our area, while the trough extension over Hawaii contributed to vertical motion and precipitation there..


A surface map 12-h later (5 AM our time) shows a front approaching our coast, while a trough (area of low pressure indicated by the dashed lines) extended back towards Hawaii,with moderate northeasterly flow that rose up the northeast slopes of Kauai.


Hawaii and the Northwest have a lot of weather connections..... atmospheric rivers (which we call pineapple expresses) are, of course, one.   But there is a lot more, including the ocean currents which, move water from off our coast to Hawaii.

And those currents will assist a brave UW student in rowing from the West Coast to Hawaii in June.
________________________________________

Announcement:  The Northwest Weather Workshop is on April 27-28

The NW Weather Workshop is the big annual meeting for those interested in Northwest meteorology.  This year we will have a major session on the meteorology of NW wildfires and others on other aspects of our regional weather.  The gathering takes place at the NOAA facility in Seattle.  To view the agenda and to register, go to the meeting website.  The workshop is open to everyone, but registration is required.


Thursday, April 19, 2018

Dense Fog: Unusual This Time of the Year

This morning brought fairly dense fog to portions of Seattle near Lake Washington and in some river valleys around the western side of the State.  The fog was beautifully illuminated this morning around 7 AM in the view looking north from the Space Needle PanoCam


And the view southeastward towards Mount Rainier was impressive as well.


The fog was apparent is the visible satellite image at 7 AM, with some of the river valleys of SW Washington in fog.


It  turns out the dense fog is relatively unusual this time of the year in Washington State.    I can show this using the following graph from my NW Weather book. Here in Seattle (red color) fog reaches the minimum number of days per year from April through June.  Spring is a low time for fog in most locations of our region.  Fall is the big fog season.

But why is Spring so bad for fog?  For several reasons.

First, most of our fog is radiation fog, which develops over long nights as the earth radiates infrared energy to space.    Our nights are getting MUCH shorter now, so much less time for the cooling to occur (remember our day-night periods today are the same as around August 23).

Second, fog likes stable conditions that does not produce a lot of vertical mixing.  Such mixing is bad for fog, since the cooling at the surface gets spread over too much air in the vertical. Stable conditions occur when temperatures don't decrease rapidly with height.  The opposite is true in Spring...the sun is fairly strong, causing the surface to warm, but the air is still cool aloft. Not stable and bad for fog.


Third, in spring around here we still have a lot of clouds and clouds slow up the radiational cooling from the surface. 

Fourth, rain is generally letting up in Spring and rain helps moisten the surface and lower atmosphere...which is good for fog.

Why fog today?  We had lots of rain recently so the lower atmosphere was moist.   And high pressure moved in late yesterday, which helped make the atmosphere more stable and lessened the amount of clouds aloft. 


Can our models forecast fog?   They can, but there skill is not great.  Fog plays into almost all our modeling weaknesses.   Here is the 14 hour forecast for low clouds valid at 7 AM from the UW WRF model.  Right idea, but somewhat too much fog/low clouds around Puget Sound.


And now the big news....a major warm up will occur early next week, with highs getting into the upper 60s on Monday and Tuesday.  And pretty decent the rest of the week.  More on the "big heat" in my next blog.

Tuesday, April 17, 2018

The Carbon Fee Initiative (1631) Has Major Problems: Let's Try Something Better

This fall, voters in Washington State will consider an initiative (1631) that, if passed, would put a fee on carbon and use the funds to "reduce pollution, promote renewable energy, and address climate change impacts."  Superficially it sounds good, but underneath the hood there are very serious problems.

In this blog, I will analyze Initiative 1631, note some its major deficiencies, and suggest a far better approach (a revenue-neutral carbon tax that would improve Washington's regressive tax structure).



As I described in my previous blog, I am a strong believer in carbon taxes and was an enthusiastic supporter of the defeated Initiative 732.   Mankind is doing too little to slow carbon emissions into the atmosphere, and a well-designed carbon tax or fee can use the free market to effectively respond to the problem.  Economists of all political backgrounds acknowledge the power of taxing what you don't want (in this case emissions of carbon) in encouraging people to make different choices.  Like driving smaller cars or switching to electric vehicles.

But Initiative 1631, whose goal is to initiate a carbon fee in Washington State, is deeply flawed and poorly constructed, and I believe destined for certain and dramatic defeat.

The Essentials

Initiative 1631 would establish a carbon fee that would slowly increase over time.  Unlike Initiative 732, it would not be revenue neutral, but would use the proceeds of the fee to support climate justice, renewable energy, retraining, and other activities related to global warming impacts.  
The Problems

There are so many serious deficiencies with this initiative, one hardly knows where to begin.

1.  How the money will be spent is vague

There are really no clear guidelines on how the money will be spent.  15%  should address the "energy burden" of poor households, 10% goes to the Tribes, 35% to environmental justice, $50 million to help displaced fossil-fuel workers, and the rest to vague goals in supporting renewables and clean energy.

Decision authority on how the money will be spent will be given to a 15-member board appointed by the Governor to four-year terms, and would include one tribal representative, one representative of vulnerable populations/health action areas, and the six co-chairs of a collection of panels.   So basically a group of liberal activists, appointed by a Democratic governor will make the decisions.

There is no strategic plan, no requirements for technical knowledge, and a guarantee the spending will be highly political.  Not only is such a group practically guaranteed to spend the funds unwisely, but such a plan would certainly lose the support of moderates and Republicans. 

Most folks are not willing to spend money when they don't know what they will get.  That is the problem of I-1631.  Can you imagine if the bill had specified real, tangible benefits?   Such as supporting the rapid build out of rail from Seattle to its eastern/northern suburbs?

2.   The Initiative Would Make Washington State's Regressive Tax Structure Even Worse

Whether the money comes from a tax or "fee", the effect is the same... to make the cost of carbon fuels more expensive. Money people will have to pay out.  Unlike I-732, the proposed initiative will not return the funds to taxpayers, but use the funds for a wide range of unspecified activities that are somewhat connected to climate change in the minds of the oversight board.   

The financial impacts of I1631 are clear:  this is essentially a new tax that is not based on income.   It will substantially raise the tax burden on everyone, including low-income folks, who are just as dependent on cars and trucks as anyone.  Thus, just like the sales tax,  it will be highly regressive, with the poor paying a higher percentage than their richer neighbors.  The media has headlined our regressive tax structure in Washington State.  I-1631 will make it much worse.

3.  I-1631 is Highly Partisan

To pass in Washington State and to serve as a blueprint for action for other states, any carbon tax or fee must have bipartisan support.  A revenue-neutral carbon tax could garner support from both sides of the aisle, as was true for for I-732.  For example, ast year, major Republican figures came out in support of a national revenue-neutral carbon tax.


Unfortunately, it would be hard to design an approach more likely to turn off Republican and independent voters than I-1631.  Not only is it not revenue neutral, but the funds are hardwired in the direction of Democratic supporters (labor, the tribes, minority and low-income "climate justice" groups).   Even worse, the control of the funds is put in the hands of an oversight committee selected by a Democratic governor.



I-1631 is designed to reject the moderate and conservative electorate (e.g., nearly all of eastern Washington and Vancouver, WA) and will not be suitable to serve as an example to the nation.

4.  I-1631 Gives Too Many Exemptions and to the Wrong Groups

To garner support, I-1631 gives exemptions to many business groups.  For example, it exempts local power companies (e.g., PSE), which is a total mistake since it represents a major user of fossil fuels.  The initiative also exempts coal-burning facilities (e.g., the Centralia coal plant), that offering perverse incentives to burn more coal, one of the dirtiest fuels.  And there a dozens more exemptions that I won't list.   I-732 did not do the exemption thing, but removed the B & O taxes to help businesses.

5.  I-1631 Starts Off With Too Little Impact

This initiative begin with a fee of $15 per ton, which would increase gas prices  by about 14 cents a gallon.   Not enough to make folks alter their lifestyle or the vehicles they purchase. Everything we know about climate change tells us that a large and immediate reduction is needed.  I-1631 starts weak, particularly compared to I-732, which began at $ 25 a ton of carbon emissions.





I could go further about the problems with I-1631, but you get the point:  this is a hopelessly flawed initiative that not only won't effectively address climate change in our state and would waste huge sums of money, but it will needlessly politicize what should be a bipartisan effort.   I should note that the key supporters of I-1631, The Alliance for Jobs and Clean Energy, the labor unions, and the Sierra Club actively opposed the revenue-neutral carbon tax (I-732).  

Why?  Clearly, because they did not gain access to the money.  With I-1691 they would.

A Revenue-Neutral Approach:  Far Superior By Any Measure

Now imagine a different approach, one in which a sufficiently large carbon tax is applied to encourage folks to reduce their carbon emissions.  An approach that would refund ALL the money back to the people so they are not taking a financial hit.  A revenue-neutral approach.

But it could be better than that, we can refund the carbon tax in a way that provides preferential relief to low-income people.  There are many ways to do this.  We might reduce the State sales tax by 1-2%, lessening the most regressive tax we have.   Or we could give everyone back the same carbon tax dividend, which would preferentially help low income folks that can't afford the carbon rich lifestyle of the wealthy.   Some funds could go into a low-income tax credit, as done in I-732.   

Our state has the most regressive tax structure in the nation.  The proper use of a carbon tax could help improve this dismal situation.



But it is even better than that.  The carbon tax could be bipartisan, bringing the State together to begin to address the threat of anthropogenic global warming.  And such a carbon tax could have legs, with the ability to spred to red and blue states around the union.

The question is not whether I-1631 will pass.    It won't.  Can you image folks taxing themselves to contribute to such a poorly designed and vague plan?  Will low-income people willingly tax themselves hundreds of dollars a year to support the vague goals of some environmental activists?  You know the answer.

The real question is what happens after I-1631 fails.  Will the environmental left that killed I-732 decide to drop their financial demands and join in a bipartisan effort to deal with carbon emissions without social engineering and giveaways to their constituencies?    We will see.  

Climate change forced by increasing greenhouse gases is too serious an issue to waste time and effort, which is exactly what 1631 will do.

________________________________________

Announcement:  The Northwest Weather Workshop is on April 27-28

The NW Weather Workshop is the big annual meeting for those interested in Northwest meteorology.  This year we will have a major session on the meteorology of NW wildfires and others on other aspects of our regional weather.  The gathering takes place at the NOAA facility in Seattle.  To view the agenda and to register, go to the meeting website.  The workshop is open to everyone, but registration is required.

Sunday, April 15, 2018

Localized Deluge

News flash:  It is 9 AM on Sunday and it should be generally dry for the next 4-5 hours.  Immediate response necessary (e.g., go outside).    There are a few residual showers, some of which are producing rainbows (see 9AM Seattle SpaceNeedle panocam).  Note the blue skies.


Yesterday was an amazingly wet day for April, and a "highlight" of one of the wettest Aprils on record.   A number of locations (like Seattle) had their wettest April 14th on record and April is now the 4th wettest on record and WE ARE ONLY THROUGH HALF THE MONTH.

The rain distribution yesterday was interesting, with the heaviest precipitation found in a southwest-northeast band from SW Washington across Seattle and into the central Cascades. 

Here are the 24h totals ending 11 PM Saturday (only showing the locations with at least 1.5 inches).   1-5-2 inches over Seattle, but 3-5 inches over SW Washington and nearly 5 inches on the western side of the Cascades NE of Seattle.  8 inches near Mt. Rainier.


The heaviest rain was during the late afternoon and early evening when local streets started to flood.

A radar-based estimate of 48-h rainfall ending 11 PM Saturday show the band of heavy precipitation across central Puget Sound, with 2-4 inches being prevalent.  And you will also notice the rainshadow over NW Washington--those lucky folks from Sequim and Port Townsend to Bellingham.


What was going on?   A relatively narrow atmospheric river of moisture that sat over us for over 12 hours.    You can see the culprit in an infrared satellite picture at 11 AM Saturday (below).


A plot of the moisture content of the atmosphere at 11 AM yesterday shows the feature, with the orange and red colors indicating high values of total moisture in the atmosphere.  Heading right towards us.


Another very useful tool can be created by multiplying the moisture content by the wind...something called Integrated Vapor Transport (IVT).   That is what really controls how much rain we get on our mountains.  IVT at the same time (11 AM) as above  shows significant values moving off the Pacific, with an configuration matching the heavy rainfall.

The forecast for the next 24 hours?  Good news for sodden Washington, bad news for Oregon.  The accumulation from 5 AM Sunday to 5 AM Monday indicates lots of rain in Oregon and northern CA, which is excellent--they need more water down there.  Washington has enough.  More than enough. Our snowpack is above normal.  Our reservoirs are full.  Our rivers are running high.  Our soil moisture is high.


I am heading outside for a run with my dog while I have a chance.