Tuesday, July 17, 2018

Marine Air Surges Inland

For those of you unhappy about the recent warm days, living in a city where AC is rare, relief is at hand.

As I speak, marine air is pushing rapidly into western Washington.  Trees are swaying, temperatures are rapidly falling, the air is moistening, and my wind chimes are ringing.   Life is good.    Our natural AC is turned on, and a night of comfortable sleeping is in store.

It has been substantially warmer than normal for the past week, with several days of high temps that were 10F or more above normal (see plot, purple line shows the average highs, cyan, average lows).  There was a bit of marine air leakage today...resulting in highs dropping 5-7F from yesterday.

All meteorologists know to watch the onshore pressure gradient--the difference in pressure between the coast (say Hoquiam, HQM) and Seattle (SEA)-- to get an idea of the amount of marine influence.  Just a small change from offshore to onshore pressure gradient can make all the difference.  Here are the pressure differences today.  Note that the Hoquiam to Seattle pressure difference rose to 3.5 hPa--that is enough to guarantee a good surge of marine air.

Winds have responded to the onshore pressure gradient. At Smith Island, in the eastern exit of the Strait of Juan de Fuca (and just offshore of northern Whidbey Island), winds climbed to 25 knots as of 9 PM.  At Race Rocks, near Victoria, it hit 40 mph.

At the University of Washington, winds have also picked up to around 10 knots (top panel).  Temperature at the UW is falling rapidly (third panel) and dew point rises (more moisture in the air).  As a result, there has been a huge increase in relative humidity (fourth panel) from 30 to 75%.  This will help reduce fire risk in the west.
The onshore flow is also bringing in the low clouds that have been waiting their chance offshore.  The visible satellite at 8 PM Tuesday shows stratus/stratocumulus pushing inland, particularly south of the Olympics through the Chehalis gap (see below).  If you live in western Washington expect to see lots of clouds when you wake up Wednesday morning.

The next few days should be typical for mid-summer--low clouds in the morning and temperatures rising into the upper 70sF during the afternoon.  Perfection.

There is a cloud in the silver lining though....with cool air and higher pressure in western Washington, winds over the eastern slopes of the Cascades (e.g., Ellensburg) should strengthen considerably, resulting in an increase potential for stoking any fires.   Even with the minor cool-down today, the winds at Ellensburg revved up quite a bit, with sustained winds reaching 23 knots and gusts to 37 knots  this evening (see plots)

Expect even stronger winds there tomorrow.

Morning update.  The cool air moved in, but was quite shallow.  Here are the winds and temperatures above Sea Tac Airport (time on x-axis, pressure on y axis, 850 is about 5000 ft).  Above that level, nearly no change in temperature, but at around 2000 ft the temperature it  is about 10C (18F) cooler.

The visible satellite photo at 6 AM shows low clouds reaching the Cascade foothills, but it is still clear in the mountains.  A hike this morning to a low peak would be glorious.....going from cool to warm and looking down on the low clouds.    But hurry!  They will burn back quickly.

Sunday, July 15, 2018

The Technology That Can Provide Society with Actionable Information For Dealing with Global Warming

The long-term impact of global warming is one of the key issues of our time.

Greenhouse gases are increasing rapidly and it is becoming increasingly clear that mankind will not significantly reduce emissions during the next few decades.
Global climate models, forced by increased greenhouse gases, suggest major changes in the Earth's climate and weather regimes, especially by the middle to end of this century. 

But these models do not provide actionable informationWhy? 

(1)  Because global climate models do not possess fine enough resolution to describe terrain, thunderstorms, and other local effects that can be critical for determining future climate change in many areas (like the Northwest).

(2) Global climate models do not necessarily agree on even the large scale impacts of climate change.    And there is also uncertainty regarding how much greenhouse gases will increase during this century.

Although global climate models have issues, society still needs future climate impact information. 
  • Infrastructure must be built or adapted to deal with changes in climate-- with examples including dams, reservoirs, drainage and water systems, coastal and riverside facilities, and more.
  • Our management of the environment, such as forests, wetlands, and the Sound, may need to be altered with upcoming climate change in mind.
  • And we may well have to alter where we live, build, and do agriculture.
Clearly, we need reliable information on how our local weather and climate will change as greenhouse gases increase.  Information that provide both our best estimates of what will happen and their uncertainties.   And we don't have it.

This blog describes a proposed effort designed to provide the necessary regional climate forecasts.  One based on state-of-science modeling that is both high resolution and probabilistic and takes advantage of the latest modeling and scientific advances.

But to make this effort a reality will take resources, both in terms of personnel and computer time.

This blog proposes the development of a regional climate modeling center and is a call for the support needed to make it a reality:  from local governments, interested local businesses, wealthy individuals, large numbers of modest investors, or perhaps a foundation.

Building a Regional Climate Prediction Effort

Global models can get large-scale features correct, but can't deal with critical, but smaller scale, local terrain, surface, and water features.  How do we solve this problem?  

Regional Climate Models (or RCMs).

The idea is to run high-resolution RCMs on small domains over an extended period, using the global models to drive the boundaries of the small RCM domains.  This is called dynamical downscaling. The high-resolution domains are small enough so that the computer resource requirements are reasonable, but high-enough resolution to get the local features correct.

Several efforts are doing this, including a group of us at the University of Washington.   Let me show you an example.  On the left below is the forecast of winter (DJF) temperature change predicted for the end of the 21st century using the ECHAM5 global climate model, assuming a continued rise in greenhouse gases.   No local details at all and doesn't look very realistic.  
And on the right is a simulation from a regional climate model driven by the global model.  You can see the influence of terrain, with areas of very large warming due to melting snow on the slopes.  Much more warming and undoubtedly more realistic.
Only  a high resolution regional climate model can realistic predict the reduction in snowpack on our local terrain, since the global models lack even our major mountain ranges (e.g., the Cascades and the Olympics). 

Long experience by my group and others suggests that a regional climate model must run with a grid spacing (distance between the grid points) of 12-km or less to start to do a reasonable job with Northwest terrain.

But then there is the uncertainty issue.  You can't simply complete one regional climate run and go home (which several groups have done in the past).   Just as in weather prediction, you must run a collection of high-resolution runs (called an ensemble), each starting slightly differently and each using somewhat different physics (how we simulate processes such as radiation, condensation, precipitation, etc.).     And we need to so a variety of runs with different amounts of greenhouses gases, since there is uncertainty of their concentrations in the future.

So an ensemble of regional climate runs is necessary to provide a reasonable estimate of regional climate uncertainties and to allow the calculation of probabilities of potential outcomes.  One also needs to complete statistical calibration (more on this later).

Our results so far

No group has attempted to create a large regional climate model ensemble, until a group of us at the UW began such an effort.  Our initial funding was mainly from Amazon, who provided 18 months of some staff support and tens of thousands of dollars of time on their cloud.  Amazon gave us a good start, but that funding has run out and our project is running on fumes now.

But we have gotten far enough in to give you a taste of the power of the approach--four of the regional climate runs are complete.  So let me give you a view of Northwest climate change that no one has seen before.

Here are four high-resolution regional climate model forecasts of total winter (DJF) precipitation at Seattle, driven by four major global climate models from simulations running from 1970 through 2100.   Black dots indicate observed values.  The model values are within the spread of the observations during the contemporary period...a good sign.  The future?   A slow, but modest increase in winter precipitation.  Good for water resources if we can store it.

How about winter temperature?   No much change between 1970 and now (consistent with observations), followed by a slow rise starting in the 2030s, with temperatures at the end of the century up by about 4-5C (about 8F).  Seattle will have much more pleasant temperatures in the winter, but that has a down side:  reduced snowpack.

Our goal is to have at least 12 of these runs done by the end of the year if we can find the funding.

What needs to be done

To provide the best possible regional climate forecasts, we need to run 30-50 regional climate simulations for the Pacific Northwest, using a full range of climate models, greenhouse gas scenarios, and variations in model physics.  We know how to do this.   And once the runs are complete we need to complete statistical calibration, including fixing biases evident over the contemporary period where we have observations (such as 1970-2015).

This is all doable within 1-2 years, but it will take resources.  Support for 2-3 personnel.  Substantial computer resources.  But doing so will give infrastructure planners in the Northwest extraordinarily valuable information and greatly assist in increasing the resilience of our region to upcoming climate change.  You can't plan for what you don't know about.

So how can we get the resources to make these regional climate simulations a reality?

Might a regional or national foundation provide the assistance?  Or a wealthy individual?  If so, please contact me.

We have appealed to state and local agencies, talking about setting up a regional climate change prediction consortium, modeled after our very successful regional weather prediction consortium.   So far only limited interest.

Individual donors can also help maintain our current efforts at this UW website.

But somehow, we must find a way to make this happen. There is so much talk about climate change,  even a carbon initiative on our upcoming ballot.  Is it not amazing that the investments have not been made in securing the best possible information regarding the impacts of climate change on our region?

Finally, I have a prepared a video that goes into more detail about the necessity and scope of the proposed effort:

Saturday, July 14, 2018

The Driest Air of the Nation is Over the Inland Pacific Northwest

People think about the Pacific Northwest as being a moist place, but during mid-summer we are often one of the driest.

An excellent measure of the amount of water vapor in the air is the dew point temperature, the temperature to which the air must be cooled at constant pressure to become saturated.  The higher the dew point, the more moisture air contains. 

Here is a map of dew point at 9 AM this morning.  The lowest dew points in the nation was in the Pacific Northwest east of the Cascade crest (around 40F).  Middle of the country and in Florida?  Around 70F--very sticky.

Another measure of humidity is relative humidity, a measure of moisture that also involves temperature.  Relative humidity tells us how much moisture is in the air compared to the maximum it can "hold".   Since warm air can hold more water vapor than cool air, relative humidity tends to drop as temperatures rise.  

Here is the relative humidity at the same time as the above figure (9 AM Saturday).  The lowest relative humidities were over the  inland Northwest (both little water vapor in the air and high temperatures) and over the interior of California and eastern Texas (very high temperatures).

Relative humidity varies greatly over the day, declining substantially during daytime as temperatures rise.    Let me illustrate this for today (Saturday) using forecasts from the UW WRF model. 

At 5 AM, when temperatures were relatively cool, the driest air is over the lower elevations east of the Cascade crest (brown colors), with higher humidity along the coast.

Big changes by 11 AM, as warming causes a huge decline of relative humidity over most of the region.

And by 5 PM, near the time of max temperatures, the region was pretty much desiccated--with relative humidities below 30% in most locations away from the immediate coast.   No wonder your mouth felt parched and you grabbed a cool drink.

10 PM tonight?  Cooling temperatures resulted in an increase of relative humidities.

In contrast, dew point hardly changed during the day.  To show this, here are the dew points for 5 AM and 5 PM today.  Pretty similar. With drier air (dew points less than 40F) over much of the the high terrain and regions east of the Cascade crest--see below.

So when outsiders tease you about Northwesterners having webbed feet and other jokes of our region always being wet, feel free to correct them, noting our wonderfully dry conditions during our near perfect summers.

Thursday, July 12, 2018

Far Less Smoke over the Northwest Than Last Year

The wildfire and smoke situation is far better over the Northwest this year and there is a good chance it can stay that way for several weeks if we are careful.

Let's start by comparing the high resolution MODIS satellite imagery for yesterday around noon and the same time one year ago (below).  This year, with the exception of some clouds, has clear skies with little hint of smoke.

But last year, dense smoke, produced by multiple fires over British Columbia, was evident over that province, with substantial amounts pushing into Washington State.

Air quality, as shown on the EPA AirNOW website, is quite good over our region today(see below).

Why has this year been better? 

We started with a healthy snowpack on April 1st, which is good.  But the key has been that June had normal  to below normal temperatures around the region (see below).  And, precipitation, and particularly thunderstorms, were below normal--thus, less lightning initiation of wildfires.

Because of the good snowpack and a relatively temperate spring (except the warm period in May), the soil and fuel moistures are relatively normal right now over fire-prone areas, with the biggest dry anomalies over the western part of the region, which is far more resistant to fires.  To show this, here is the  current Palmer Drought Severity Index, which integrates past temperature and precipitation to give a measure for the moisture content of surface layer.  Not too bad over eastern Oregon and Washington.

The forecasts over the next week are favorable.  We should be dry, but not excessively warm, with highs getting into the lower  to mid 80s over western Washington.  The latest ensemble forecasts indicate high pressure building over the West Coast, but of modest amplitude (see forecast height anomaly--difference from normal--at 500 hPa from the GEFS ensemble below).

We will be dry....but paradoxically that could be a good thing in the short run, with no thunderstorm and lightning activity over the Washington and much of Oregon.  The UW WRF accumulated precipitation for the next week is shown below.  Only southern Oregon will get some lightning... and the fire folks need to be ready for that.

So what about new fires in the weeks ahead? 

It will be up to us.   The moisture content of "fuels" will slowly drop, enhancing fire danger.  And it is clear from the recent grass/sage brush fire near Vantage that some of the grasses at lower to moderate elevations are ready to burn right now.  So we have to be careful (no fireworks, no throwing lit cigarettes out of cars, no target shooting, campfires, and off-road vehicles in vulnerable locations, etc.) 

But we should not forget that fire is entirely natural in our region and much of the problem is created by us.   We are pushing our homes deep into the wildland--locations that have burned frequently for millennia.   We have mismanaged our forests, including suppression of fires and allowing them to grow into explosive tinderboxes.  And we should never endanger young men and women to save isolated homes when wildfires are raging. 

For too long, many in the media and some politicians have waved the climate change banner when wildfires have occurred, neglecting to push the necessary actions on the ground (e.g., stopping development in remote areas, thinning and burning forests).  My field can help immensely by providing forecasts of dangerous situations (like major wind shifts, upcoming lightning events), but in the end some difficult and expensive choices need to be made.

Monday, July 9, 2018

Beautiful Cloud Pictures of a "Cap" on Some Cumulus

Over the weekend two people independently sent me pictures that amazed them...and they were looking for an explanation.

The first was from Ellen Baker from Glacier, Washington taken late Friday afternoon.  There was a growing cumulus with what appears to be a lenticular ("lens shaped") cloud right above it.

 And here is one taken by Catherine McConnachie around Marrowstone Island on Friday evening.  A bit different, but the same idea...there appears to be a lenticular cloud right above a growing cumulus.  And these clouds have soft boundaries...they are made of ice.

What is going on?   How can you get a lenticular cloud without a mountain barrier?

You can....and these are called Pileus cloud (which means "cap" in Latin).

This is how it works.  Cumulus clouds, particular growing cumulus congestus clouds as seen above, are associated with strong upward motion.  This upward motion can push the air above the cloud upwards.  Air being pushed upwards cools because it expands as it shoved toward lower pressure, since expansion is associated with cooling (like air coming out of bike or car tire).   If that air aloft is relatively moist and close to saturation, the cooling can cause the air to saturate, producing clouds.

OK... let's see if this makes sense.     Here is the upper air sounding on the WA coast for 5 PM Friday.  Temperature is in red, dew point is in blue and the air is saturated with they are on top of each other.  The height coordinate is pressure, with 500 being about 18,000 ft and 700 about 10,000 ft.  The cumulus in the picture were perhaps 10,000 to 15,000 ft high.    The air was pretty much saturated to 550 hPa (about 17,000 ft) and fairly close to saturation in some layers above (e.g., about 450 hPa).    Strong lifting from the growing cumulus could have lifted and saturated that upper layer--which as cold enough to form clouds made of ice.

Pileus clouds are more frequent that you might think, so keep you eyes open for them.  And now you know a new Latin word.

Saturday, July 7, 2018

Real Summer Begins in the Pacific Northwest on Wednesday

It is one of the interesting oddities of living here in the Pacific Northwest, and particularly living west of the Cascade crest.

June can have lots of clouds, and occasionally murky conditions can extend just beyond the July 4th weekend.   

But then something wonderful happens:  the clouds fade away, temperatures rise, and the chance of precipitation plummets.  A magical period from roughly July 10 through early September when the coastal half of the Northwest has the best weather in the nation.

And it is going to happen right on schedule this year.  But there is a dark side to this perfect weather:  the potential for wildfires.

To illustrate typical conditions, here are the typical daily probabilities of measurable precipitation (at least .01 inch) at Seattle-Tacoma Airport.  About 27% in late June and early July, but plummets to around 10-12% (and sometimes less) by mid July. 

Best time for a wedding or outdoor party?  The last few days of July!

The excellent weather.com forecast for Seattle shows a transition to sunny skies and essential no chance of precipitation starting on Wednesday, with temperatures increasing into the mid-80s.    Warm, but not too warm, and dropping into the 50s at night.  You will be able to sleep well, particularly if you have a fan.

But as I have talked about many times in this blog, one should always think probabilistically about forecasts, which means using ensembles of many forecasts.   Below are the ensemble forecasts from the North American Ensemble Forecasts System (NAEFS) that combines roughly 40 model predictions from the Canadian and U.S. global ensembles.   The predictions are for Seattle, with the horizontal line showing the median of the ensembles, the "whiskers" showing the range of the forecasts, and the yellow box indicating 50% of the forecasts closest to the median.

The forecast shows relatively cool temperatures through July 11th (Wednesday) but nice and warm after that (20C is 68F, 30C is 86F).   A chance of light precipitation early in the week as well as some clouds... then dry and mainly clear.

Portland? Similar story, but a bit warmer.

Spokane?  No precipitation.  Temperatures getting into the uppers 80s to low 90s and not much clouds.

The 72h total rainfall ending 5 PM Friday shows nothing over Washington State and most of Oregon.

The downside of all this?   The surface fuels (e.g., grasses, small bushes, debris on the forest floors) are going to dry out quickly during the next few weeks.  Right now fuel moisture is in the normal range, but that won't be true by the third week of the month.   The potential for wildfires will increase substantially.

One good thing is that there won't be much lightning, which is a major igniter of wildfires, particularly in remote locations.  So people will have to be very careful not to start fires.  No fireworks, no practice shooting in rural locations, only carefully controlled cooking fires, etc.

Thursday, July 5, 2018

Profound Impacts of Fireworks on Visibility and Air Quality

The visibility this morning was greatly reduced compared to yesterday and fireworks smoke played a major role.

Here is view from the Seattle PanoCan looking towards the Cascades at 9:30 AM this morning (Thursday, July 5).  Very hazy with the foothills barely visible.  The haze is from fireworks.

The day before at the same time (July 4th, of course).  Some clouds aloft, but MUCH better visibility.  You can even see Mt. Rainier.

Now you don't have to take my word for the existence of plumes of smoke from fireworks.... lets take a look at the observations taken by the Puget Sound Clean Air Agency.  Here is the amount of small particles in the air (PM2.5) on Seattle's Beacon Hill.  Huge and sharp increase of particles during the evening of July 4th, to values over 100 (micrograms per cubic meter).  This is in the unhealthy level.

But why was in hazy this morning looking east?  To figure this out, let's examine the particles levels at Bellevue (brown line) and North Bend, near the Cascade foothills (green line).   Big increase during the evening of the fourth, but the levels stayed relatively high!

I suspect a lot of the smoke over the populated area near Puget Sound got pushed towards the east this morning.  In fact, the time-height cross section of wind and temperature at Seattle Sand Point provided by Puget Sound Clean Air Agency (see below) does suggest this (below).  The winds were easterly during the afternoon  but switched to westerly at low levels for several hours overnight  (heights are in meters ASL, time in UTC increases to the left)

And don't think Seattle was the only place with smoke.  It was worse in Tacoma and Marysville, home of Boom City, had a problem as well (see below).

Last time I was watching the Lake Union fireworks display with students, staff, and faculty on the top of my building, and the smoke became increasingly extensive during the short show. 

By 11 PM, the smoky scene was beginning to look apocalyptic.

Several people told me they felt cold-like symptoms this morning from the left-over smoke.  In any case, air quality will improve rapidly now as a Pacific front moves through bringing an influx of clean, marine air.   

Finally, there may be a superior replacement for the smokey fireworks---performances of hundreds of drones with LED lights.    Check out this video to see what I mean.