Thursday, July 20, 2017

What are these clouds?

I received nearly a dozen emails with pictures from folks interested in the clouds apparent around 5-7 PM last night (Wednesday).  Some examples:

Picture courtesy of Nancy Flowers

Picture courtesy of Dyana Stevens

Seattle PanoCam 6PM

What was going on?  Yesterday, a weak front was approaching and this feature was associated with an upper level trough coming off the Pacific (see 500 hPa--around 18,000 ft--map at 5 PM Wednesday).  Such an upper trough causes

upward motion that can promote clouds and instability in the middle troposphere).  In fact,  the vertical sounding at Quillayute, on the WA coast, at 5 PM Wednesday, shows a nearly saturated layer between roughly 500 and 300 hPa (roughly 18,000 ft to 30,000 ft).


As a result, some altocumulus clouds (middle level puffy instability clouds) formed and were vigorous enough to start precipitating out ice crystals.   The long tails of precipitating ice are called fallstreaks or mares tails.   They get distorted and curved by the change of wind with height (wind shear).

So the bottom line is:  folks saw precipitating altocumulus clouds forced by an approaching upper level trough.




Finally, if you want to see an absolutely stunning weather video dealing with clouds and precipitation in Arizona, check this out.   Heroic music, gorgeous imagery....it may bring tears to your eyes.

The Weather of Arizona - A Time Lapse Film from Bryan Snider Photography on Vimeo.

Tuesday, July 18, 2017

Smoky British Columbia and Will Wildfire Smoke Affect Eclipse Viewing?

After a recent bout of lightning, a number of major fires were initiated over British Columbia.  As shown by the NASA MODIS satellite imagery over the past three days (see below), the smoke plume have been impressive.





Wildfire/smoke season has begun over the Pacific Northwest, with most of the smoke so far heading eastward.

But the question of many is whether smoke will be a factor during the August 21st eclipse.   There is a lot of talk of folks converging around Madras, Oregon, east of the Cascade crest, but is there a downside to that location: smoke?

To get some insight into this question, here is the climatological probability of a significant wildfire s created by the NOAA/NWS storm prediction center.  A fairly significant chance (10-20%) for a wildfire being around on August 21st around NE Oregon, including the Madras area.

And to illustrate the threat, here is a MODIS image for August 22, 2015, showing a wildfire that spread smoke over the area.


Now smoke will not take out the sun, but it could seriously degrade viewing of the corona and solar prominences.   The lack of rain of the past month is progressively ratcheting up the fire risk for later in the season.   Something to watch.
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Announcement:  Atmospheric Sciences 101

I will be teaching Atmospheric Sciences 101 this fall if anyone is interested either as a UW student or the Access Program for those over 60.  This is a general intro to weather and weather prediction.  MTWTh 10:30-11:20, Kane Hall.


Monday, July 17, 2017

Melt Out at Paradise on Mount Rainier

Yesterday, July 16th was melt-out day at the official snow measuring site at Mount Rainier.


Located at roughly 5500 ft, this melt-out day is about 1 week later than typical for the past 100 years (information from Mark Albright, UW Research Scientist).  Here is an interesting table showing the mean melt-out dates by decade at Paradise Mt Rainier:

Decade     Date     No. of Years
----------------------
1910s       16 July     2*
1920s       10 July      9**
1930s        3 July       10
1940s        1 July       10
1950s        17 July       9**
1960s        5 July        10
1970s         21 July      10
1980s        10 July       10
1990s        15 July       10
2000s        10 July        10
2010s         1​6 July      8***

* 1917 and 1918, ** 1925 missing, 1950 missing, *** 2010-2017

As you can see, there is no real trend towards earlier melt-out, which would be a sign of global warming.  That will come, but later in the century.

What about a much lower site?  Such as Stevens Pass (about 4000 ft above sea level)

The snowpack melted out this year on 7 June 2017 at the Stevens Pass SNOTEL site, with the melt-out this year tied for ​11th ​latest out of the past 37 years (the length of record there).

Mean melt-out dates by decade showing a trend towards later melt-out of the snowpack in recent years:

1980s: 30 May
1990s: 1 June
2000s: 2 June
2010s: ​4 June (thru 2017)

Similar to Paradise, the snowpack is holding on later into the warm season.  

 The maintenance of our snowpack into the summer helps maintain our streamflow into the summer, which is good for fish and water resources.   By the middle of the century we expect the situation to change as warming causes more of our precipitation to fall as rain in the mountains.

Saturday, July 15, 2017

How Western Washington's Temperatures are Controlled By the Pacific Ocean

Have you ever thought about how boring and relatively unchanging our high  and low temperatures are?  Particularly, when we are in our normal situation with modest onshore (westerly) flow?

To illustrate, here are the temperatures at Seattle Tacoma Airport for the last two weeks (red lines), with the typical highs and lows.   We had a warm spell (6th and 7th, highs around 85F) when we had a bit of offshore flow, but most days reach their max between 70 and 80F, with the long-term average in the low to mid 70s.  The low temperatures are MUCH more uniform--roughly 53-58F.
In contrast, a location like New York City, also on a coast, has huge variations, with the low temperatures ranging from 80F to the upper 60s.  So why are we different?
The answer is the Pacific Ocean and the typical onshore flow at low levels during our summer.

During the summer, high pressure is typically resident over the eastern Pacific Ocean, with lower pressure inland, resulting in gentle onshore flow at low levels (see example for Monday, July 10 at 5 AM).

So the air reaching Seattle and western Washington had been over the Pacific Ocean for a long time, with the air near the surface taking on the temperatures of the ocean surface.

So what are the ocean temperatures off our coast right now?  Here they are (below).  Roughly 14-16C (57-61F), with some colder water from upwelling (water coming up from below) right near the coast, and a bit colder water offshore.  So roughly the upper 50s.  This is the kind of air that is flooding our region at night, without solar radiation to warm it up.  During our short (and generally clear) nights, there is radiational cooling from the surface, so that can take off a few degrees.
Not only are our temperatures relatively uniform, but so is the humidity or moisture content.  Our air can't pick up much moisture over the water because it is relatively cold...a very different story than that warm Gulf of Mexico.  Thus, our  dew points (the temperature you must cool air to get saturation) are typically no more than the lower 50sF during the summer.  That is important, because high dew points can keep the temperatures up at night (like in the humid East Coast).

So there is no real mystery what our temperatures typically drop into mid to upper 50s at night...and do so in a very reliable way.  It is the Pacific and its modest temperatures.

But why do we have highs in the 70s during the day when we have onshore flow and relatively clear skies, like the last few weeks?

Yes, it is the Pacific again.    We start off with a water temperature of say 57F (14C), with the nearby air of similar temperature.   Over the ocean, without surface heating, the lower atmosphere is relatively stable, with only a small change of temperature with height.  With high pressure dominating the eastern Pacific, there is sinking air in the middle to lower troposphere, which weakens towards the surface.  Such sinking tends to produce stable conditions and often inversions (temperatures increasing with height).

The temperature sounding Friday morning at Quillayute on the Washington Coast illustrates this.  Red line is temperature and heights are in pressure (700 is about 10,000 ft).  Click on the image to expand.


The typical lapse rate (change of temperature with height) along the coast at the radiosonde site at Quillayute  during the summer is roughly 3.5C per km (the graph is from the sounding climatology page of the NOAA Storm Prediction Center). The black line are the average values.


So if the temperature at surface is 15C, the temperature at 1.5 km (about 850 hPa) is roughly 5.25 C less. Let's call it 10C.  That air blows in over Seattle and western WA.

Now why do I care about 1.5 km and 850 hPa?

Because during the day over land, surface heating causes the air to mix in the vertical and it usually reaches that height.  That mixing is associated with a lapse rate (the adiabatic lapse rate) of  9.8C per km.   To put it another way, air coming in over the ocean can be mixed down to the surface, where it is warmed by compression by 9.8C per km.  Or to say it differently, the air is warmed by roughly 15C as it descends 1.5 km to the surface.  If the air started at 10C, it would be 25C at sea level.   25C is 77 F!  Our typical high temperature during the middle of the summer.


I know this explanation is a bit complicated.

But the bottom line is that we have the sea surface temperature offshore driving the surface air temperature over the ocean.  That is connected with temperatures of air in the lower atmosphere that moves inland, which can mix to the surface during the day.  The result is a direct connection between the temperature of the sea surface of the eastern Pacific and our high temperatures.  At night, when vertical mixing is minimal the connection is more direct, with low level air just moving in horizontally.

Offshore flow changes everything... our temperatures become disconnected from the slowly changing ocean temperatures, and we can get much more extreme temperature variation. So thank the ocean for our perfect summer temperatures.  And it is this connection with the ocean that will slow the impacts of global warming over our region, giving us more time to deal with that issue.






Thursday, July 13, 2017

Will You Get Free Windows on August 6?

Nearly every day lately there is a huge color advertisement in the Seattle Times offering FREE WINDOWS for your home if the temperatures reaches 89F on Seafair Sunday (August 6th).  Here is an example:


Several people have asked my take on it...so here it is.   I emailed the advertiser to get the exact rules.   IF you have already ordered windows from them and the temperature reaches or exceeds 89F at Seattle Tacoma Airport on August 6th, the windows will be free.

So, what are the chances you can win big on those new triple-pane beauties?  Is this a good bet?  Let's check the climatology at Seattle-Tacoma Airport, where data is available from 1948 to now.   Thus, we have 69 years to look at.

It turns out that maximum temperature reached 89F or more at Sea-Tac  ONLY ONCE during that period--91F in 1972.  

So based on the climatology of Sea-Tac, there is only a 1.4% chance of securing those free windows.    The odds look awfully good for the "house."  


Some of you might argue, that global warming might be helpful in winning this bet and that climatology might be giving us an underestimate of the probability of getting to the magic 89F.  Good point.

Looking at several regional stations, the warming trend over the period was about 1F.  Not enough to make a huge difference.  Make it a 2% chance.

It appears that the odds provided by our friends in the window industry would make casino operators blush.

Typical chances of winning at blackjack is 46%.

Roulette?  Pick a single number and your chances are 1 in 37 or 2.7%.  Much better than the odds given by the window folks.  So buy the windows if you need them (I could use some myself), but don't expect to get free ones.

Now if already signed up for deal and were thinking of giving the Sea-Tac thermometers a little "help", keep in mind that the sensors are between the runways at the airport, and there is probably little chance of bribing the National Weather Service technicians who calibrate the thermometers.  Call me if you want their telephone numbers.



Tuesday, July 11, 2017

New Study Suggests Global Warming Will Be Kind to the Northwest: But There Will Still Be Impacts

A recent study published in Science Magazine by Solomon Hsiang and others completed an economic analysis of the economic effects of global warming by the end of the century (2080-2099). They considered a range of impacts, including agricultural, property and violent crime, mortality, and coastal issues (sea level rise, storms), among others.  Doing so, they created a map of total economic damage, shown below (in percent of Gross Domestic Product, GDP).  Red and orange colors signify global warming will cause damage, while green colors indicated that global warming will be an economic plus.  They drove their economic models with output from climate simulations.

The bottom line is that cool states come out ahead, while warmer locations are hurt by global warming. Not good for the southeast states (particularly Florida and Texas) and most of Arizona.  But generally quite good for the Pacific Northwest.   Only a thin strip on the eastern slopes of the Cascades has a slight negative impact and the coastal zone does quite well. 
Hsiang et. al, 2017 Science Magazine

You can see some of the component contributors below.  For our region, big gains in agriculture from the added warmth.  Large drops in mortality (cold is a killer).  Far less energy costs for heating.  No increase in coastal damage because our land is generally well above sea level.


Hsiang et. al, 2017 Science Magazine

It is interesting to compare the Hsiang et al economic analysis with one examining meteorological threats from global warming  found in one of my earlier blogs (see below).  Each color represents a different threat (e.g, red would be storm surge from hurricanes).  The white area indicates one area of little increase in threat:  the Pacific Northwest.


So the Northwest is an area that should do particularly well under global warming-- we will have plenty of rain, a bit of warming will be welcome over much of the area, our storms should not become more severe, and sea level rise is not much of a problem.  Hsiang et al suggests we will come out ahead economically.    

But I am not sure that paper considers all the costs.  Warming will bring less snowpack in the mountains as the freezing level rises, so less snow melt available in the summer.  Thus, we will have to either learn to be more efficient with water (e.g., more drip irrigation in eastern Washington) or build expensive dams and reservoirs (costing billions of dollars).

Although the total precipitation will not change dramatically (small increase), we do expect the heaviest events to bring 30-40% more rain...and thus more flooding.  Thus, we will need to move folks away from rivers, something that could easily cost billions more. And away from steep slopes (like Oso).


Our east-side forests are in terrible shape due to fire suppression and poor forest practices (clear cutting rather than thinning, leaving slash, etc).  As a result, we have seen increasing number of large, intense fires, and local warming will make this worse.   We thus need to spend billions more to restore our forests to better shape to prepare.

So global warming will cost us in these and other ways; as a result, the benefits of lower heating bills, less ice/snow on the roadways, and enhanced agriculture will be balanced in part by steps needed for adaptation.

Global warming will probably end up being a wash for us.  But this will not be true of those living in warmer sections of the U.S., and for much of world's population that lives in he subtropics (such as India, SE Asia, Africa's Sahel, and Mexico).  Thus, the moral imperative is for us to reduce our carbon emissions, while at the same time building the climate resilience of the region.
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Atmospheric Sciences 101:    I will be teaching the introductory weather class this autumn (10:30 AM, Kane Hall, UW).   Open to UW students and the community (and inexpensive to audit if you are over 60 through the UW Access Program).

Friday, July 7, 2017

A Very Dry Start to Summer

For much of the Northwest, it hasn't rained since mid-June, when we had an unusually heavy one-day deluge of over an inch (see accumulated precipitation at Seattle Tacoma Airport over the past four week, red is observed, blue is normal).  Interestingly, because of that one-day amount, the last four weeks had nearly normal rainfall!
A map of the total precipitation over the past two weeks shows less than .1 inches over most of the western U.S., with most locations getting nothing.

The departure from normal shows .75 to roughly 2 inches below normal over western Washington.  The departures from normal are not large because we get very little precipitation this time of the year.
In fact, we are now entering the driest time of the year in the Northwest, with the lowest precipitation amounts the last week of July and first week of August (see climatology for Seattle)

 The models are forecasting little or no precipitation for the next few weeks.
For example, the 21-member NOAA/NWS GEFS ensemble (many forecasts made to explore uncertainty) show virtually nothing for the next 192 hours.

 The even larger NAEFS (US plus Canadian) ensemble shows the same thing  through the 21st (second panel)
 And the larger European Center ensemble indicates no precipitation or a few hundredths (gray colors) during the next ten days.  The bottom panel is the ensemble average... maybe a slight misting on Monday.

With above normal temperatures and no rain, the demand for water in Seattle has increased substantially (see Seattle SPU graphic)--see the red line.

This year has certainly been one of contrasts:  the wettest winter for many and now a very dry early summer.

Wednesday, July 5, 2017

Should Personal Fireworks Be Banned?

It causes over 10,000 injuries a year involving going to an emergency room, including loss of life, limbs, and vision.  Or permanently degrading some individual's  hearing.

It results in over 15,000 fires per annum, destroying homes, businesses, and vehicles and  causing wildfires that affect thousands of acres.

It seriously pollutes the air with particles and toxic chemicals, undermining the health of those with asthma and heart disease. 

It scares dogs and cats, causing some to cower in the corner or run away.

It can seriously disturb some of our veterans, particularly those with PTSD, bringing on terrifying memories and fear.

It ruins the sleep of many and breeds a disrespect for the law.


You would think we would finally act regarding something that was so profoundly negative in so many ways.  But we don't.  We tolerate personal fireworks.  

And perhaps it is time to get serious about stopping them.

Today, I checked the small particulate levels in our air....the kinds of particles that move deeply into our lungs (PM2.5).   The pollutant numbers surged in Seattle and Marysville and went crazy (nearly 160) in Tacoma.  And many of the fireworks have toxic chemicals and heavy metals.


According to Puget Sound Clean Air Agency, the air was dangerously unhealthy all over the south Sound last night and during the morning hours.

The news was full of the normal results of careless fireworks, including several homes seriously damaged and unlivable.  Among the fires was one in Magnolia and a two-alarm fire in Renton.

Renton Fire:  Picture credit Mike Perry

Magnolia Fire:  KING TV

Every year several young people lose fingers and other serious injuries from fireworks in our area.


And a number of stories talk about fireworks be unsettling to combat veterans.


The effects of fireworks on many pets is profound, producing terror and hiding in closets and under beds.   The fear was obvious in my small dog last night.

Sleep?   Forget it.  My neighborhood in North Seattle sounded like a war zone, with big explosions going off until 2 AM on Tuesday morning.  The vibrations were so profound on the fourth of July that my neighbors car alarm went off.  In Tacoma an apartment complex was burnt down and cable service was cut off for 10,000 customers.

Fireworks put a huge amount of debris into our waterways and in our parks, with obviously negative impacts on wildlife.

Picture credit:  West Seattle Blog
Puget Sound beaches were full of debris (picture credit, NC Pizza)

And it breeds disrespect for our laws and law enforcement.   It is clear that police are looking the other way on July 4th....not enforcing absolutely explicit laws.

So why do we continue the carnage, damage, and scared pets?   Particularly when folks can enjoy a wide collection of professional community displays?

Personal fireworks are illegal in much of the State, including Seattle, so why do the police allow it?  None of the official excuses make sense (e.g., the difficulty in catching people in the act).  Go to any of the major parks, especially ones in the water. (e.g., Mathews Beach Park), on the evening of July 4th.  Catching fireworks felons would be like catching fish in an aquarium.   But before the police did that, an announcement of a no-tolerance policy should be made at least a month before, to discourage folks from stocking up.

The biggest source of fireworks is probably the native american "boom cities", such as the ones in Marysville and Auburn.   Clearly, the State needs to work with the tribes to end the sales of fireworks there.  It is demeaning to the environmental traditions of native americans to degrade our environment with toxic smoke and noise.


Some folks may argue that fireworks are part of "Americana" and independence day traditions.    But no one is arguing to get rid of public displays.   But is the "fun" worth deaths, injuries, and burned down homes?   Of loss of hearing and inducing fear in our pets and vets?  I don't think so.   Why not start new traditions, like the use of colorful LED lights or special July 4th drones, with special lightning?

It is time that society gets serious about banning personal fireworks.

Monday, July 3, 2017

Why is Puget Sound cloudy when the rest of the region is clear?

It just isn't fair.   While nearly the entire region basked in sunshine, the Puget Sound basin had considerable cloudiness, breaking to partly cloudy skies for a few hours.   The satellite image at 3:40 PM tells the story (see below).  Even the coast had less clouds!

All the clouds caused the temperatures to cool down today, with much of Seattle not getting beyond the lower 70s.  This chilling story is illustrated by the UW Seattle weather observations for the last 3 days (below, time increases to the right).  The third row show temperatures (black line)--clearly cooler today.  The bottom row shows solar radiation.  On Saturday and Sunday we had clouds in the morning, but they were pretty much gone by noon.  Today, the solar radiation was suppressed much of the day.
This Puget Sound cloudiness in summer is not rare...here is another example, from June 20.  I could show you a dozen more.


So why all the cloudiness over Puget Sound?  A plot by Jeff Bezos to keep his minions working?  No.  It is the result of northwesterly flow and a very big obstacle--the Olympic Mountains.

The flow approaching the coast this morning and early afternoon was northwesterly (from the NW), as shown by this short-term forecast for surface winds and sea level pressure (solid lines) for 8 AM.

An expanded version over Puget Sound shows the convergence quite clearly (the winds are parallel to the wind barbs):


 NW flow is blocked by the Olympics, moves around the barrier to the north and south, and then converges over Puget Sound...a summer version of the Puget Sound convergence zone.  If air converges at low levels, it is forced to rise, causing cooling, increasing relative humidity, and eventually condensation into clouds.
      Here is the relative humidity forecast for 11 AM at 5000 ft. White is at saturation (100% RH).  You see the problem?  High relative humidity over Puget Sound and the western foothills, where northwesterly flow is forced to rise by the Cascades.


What you really want to know is about tomorrow.  Will the Puget Sound gunk stick around?    I have good news.  The answer is no.

Temperatures should increase by about 5 F on Tuesday and there will be far fewer low clouds.    The latest model run shows that some high clouds, now over the Pacific (see satellite image Monday evening), will move in over the region...but won't be a problem for the fireworks or anything else.


So enjoy the fourth..conditions should be excellent for the fireworks anywhere in our region.