Sunday, June 30, 2019

Freezing Temperatures and Puffy Cumulus Clouds

Before I discuss the impact of cold air aloft, let me show you a shot of the beautiful sunrise of Saturday morning for the Seattle PanoCam.   Love the reflection off Lake Union.

For the past several days, unusually cold air, associated with an upper level trough has been positioned over our region, resulting in cold nighttime temperatures east of the Cascades and puffy cumulus clouds over much of the region.  Below is a nice example from North Seattle Saturday morning.

An upper level chart (500 hPa, about 18,000 ft above sea level) for Friday morning shows the upper level trough (solid lines) and the cold temperatures (blue colors) over us.

With cold air aloft and relatively clear nighttime skies, some locations in western Oregon/Washington dropped into the mid-40s, while some locations in eastern Oregon plummeted to freezing Friday and Saturday morning (Saturday mornings lows shown below).

With cold air aloft and strong heating from the powerful near-solstice sun, there has been a large change in temperature with height (a large lapse rate).  This leads to instability--up and down motions in the lower atmosphere--as the atmosphere start to convect.    Such convection leads to the puffy white cumulus clouds, which form in the upward motion.   

The convection is enhanced over high terrain (which acts an elevated heat source).   A visible satellite image shows the cumulus clouds from space--you can see how high terrain is favored.

The troughing/low pressure aloft is weakening today, but should re-strengthen by Tuesday (see upper level map at 2 AM Tuesday)

As a result, precipitation is not over for us--with showers quite possible on Tuesday.  The accumulated precipitation through 5 AM July 4th, show substantial amounts over NE Washington and BC, with some extending down to Portland.

July 4th?   Looks dry over western Washington, with highs in the mid-70s.   Perfect for outdoor activity. 

Friday, June 28, 2019

A Quieter Than Average Wildfire Season So Far

With all the talk this spring of a severe and early wildfire season in the Northwest, the opposite appears to be occurring.  Currently, there are no major fires in Washington or British Columbia, with one small fire (140 acres) in Oregon.

Compare this situation to last year, when there were already a number of large fires in British Columbia.  As shown by the NOAA HRRR smoke model, the air is smoke-free over the Northwest (there are fires over the Southwest)

Looking more broadly, the Year to Date fire statistics for the entire U.S. (from the U.S. Interagency Fire Center) shows that there have been less fires and less acreage burned this year than any time in at least 10 years (see below).  But for the Northwest, it is even better than that, since most of the fires so far have been Alaska.

A key factor in this smoke free situation has been the normal weather conditions with precipitation and clouds that we have "enjoyed" much of the month.  Of particular note has been a persistent trough of low pressure over the region the last few weeks.  As a result, fuel moistures have been reasonable and the official North American fire danger map shows low danger over much of the Northwest, BC, and Alberta.

Proof of this benign situation has been the lack of fire starts after we got hit hard by lightning the last few days.  For example, here are the lightning strikes during the past two days from the national lightning network. Impressive for our region.

And the precipitation and clouds are not over.  Although we will have breaks with sunny skies and normal temperatures, the trough is going to hang around.  The European Center ensemble for precipitation through 5 AM Monday July 8th, shows plenty of precipitation in BC and northern WA. over the next 10 days.

At this point, it is becoming clear that there won't be a big early start to the fire season in BC.  Southern Oregon and N. CA have been wet, so fires will be delayed there.  I believe we can look forward to at least a month before significant fires and smoke will be in the picture.  Quite possibly longer.

And, as I have noted before, the long-term forecasts are favorable, with the International Subseasonal Ensemble (IMME)  and US CFSv2 models suggesting normal or wetter than normal conditions over the region (see below)

There has been quite a bit of hype and exaggeration about a very bad smoke season this year (from some unnamed politicians and media outlets).  Reality looks far better.  And even though things look favorable at this point, it is always good to prepare--like getting a top-of-the-line furnace filter, a N95 face mask, and the like.

Wednesday, June 26, 2019

Potentially Severe Thunderstorm Threat Today for Washington and Oregon

The NOAA/NWS Storm Prediction Center has a severe thunderstorm warning out right for for large portions of Oregon and Washington (see below)

And the the 1 PM radar showed storms moving northward on the western side of the Cascades.

The anvils from the approaching storms was apparent at 1 PM from the SpaceNeedle PanoCan.

This morning's forecast models predicts quite an event this afternoon.  The UW super-high resolution (4/3 km grid spacing) WRF model indicates major thunderstorms on the western slopes of the Cascades at 2 PM.

And by 5 PM, western Washington is covered, as well as the northern Oregon Cascades and portions of southeast Washington.

Why all the action?   The atmosphere is relatively unstable, with high levels of CAPE (Convective Available Potential Energy)--some places of 1000 J per km (blue colors).

And there is upward motion associated with an upper level low on the coast (see 500 hPa, ~18,000 ft) map below.

The problem of these events for thunderstorm lovers in Seattle is that the storms tend to weaken rapidly moving west from the Cascades--but we well might enjoy a few showers from the convection and maybe a few boomers.

Enjoy the show.

Monday, June 24, 2019

The Best Estimate Yet of the Impact of Global Warming on the Pacific Northwest

During the past month, a group of atmospheric researchers in my group at the University of Washington have completed a series of high-resolution climate simulations that probably represent the best estimate to date of what global warming, forced by increasing greenhouse gases, will mean for the Northwest.
CO2 is increasing more rapidly then ever

This blog will explain what we have done and how it provides a superior tool for determining the regional implications of anthropogenic (human-forced) climate change.  Securing a realistic estimate of the local impact of global warming is critical if we are to take steps to ensure resilience to the expected changes.  And yes, it might motivate folks to reduce their carbon footprint (like reducing jet travel, using mass transit more, etc.)

Before I begin, let me note that much of this work was sponsored by an Amazon Catalyst grant, which supported two UW staff members (Richard Steed and Jeff Baars) who ran and analyzed the simulations.   Amazon also provided substantial cloud computing resources.

Most estimates of climate change begin and end with global climate models, which include both atmospheric and ocean modeling components.  These global models are driven by estimates of how greenhouse gases, like CO2, will increase in the future.

But there is a problem.  To run globally for a century or more, the climate models must sacrifice spatial resolution.  In fact, most global models are run with grid spacing of around 150 km, which makes them unable to simulate the impacts of the crucial terrain and land-water features of the Pacific Northwest.  

We are talking about no Cascades, no Olympics, no Puget Sound or Strait of Juan de Fuca.  Even the Rockies are too low and smeared out.   Not good.  One thing my group at the UW has shown is that you have to run weather prediction models with roughly 12-km or better grid spacing to have any chance of getting our local weather and climate correct. The picture below illustrates the difference in terrain between a climate model (e.g., NCAR's CCSM4) and a higher-resolution weather prediction model.

A number of research projects have only made use of one or two climate models.  But each model has its uncertainties and biases; it would be far better to look at a collection (or ensemble) of model results--just as it is better to look at an ensemble of weather prediction forecasts.

The UW Effort:  An Ensemble of High-Resolution Climate Simulations

To address these issues, our group took on a complex task:  to run a high resolution weather forecast model for 130 years (1970-2100).   But instead of running the high-resolution model globally, which would have required impossible computer resources, we ran it over a domain that includes only the Pacific Northwest (see domains above).  And we did this 12 times, each driven by a different climate global model, allowing us to get a handle on the uncertainty in the climate forecasts.  There are fancy names for what we did:  dynamical downscaling or regional climate modeling.

We started with the several dozen global models that were part of the international CMIP-5 effort and selected the twelve that verified the best over the eastern Pacific during a contemporary period (1970-2000) and had output every six hours (which we needed to drive our regional climate model).

But we had a major decision to make.  How aggressive an increase in greenhouse gases should we use?   Should we assume that folks would "get religion" about climate change and radically reduce their emissions or should we use a "business as usual" continuation of recent trends?

We decided to go with the latter, in order to delineate the worst case.  So we used the RCP 8.5 scenario, which assumes continued increases of emissions (see below).   For the next few decades, the emission scenarios are all similar, since

 mankind can't change our energy technologies quickly, but by the end of the century the differences are large. 

Let me say, that I believe that the RCP 8.5 scenario will turn out to be too pessimistic (aggressive) by the middle to the end of the century.  I suspect that advancing technologies (like better photovoltaics, the advent of fusion power, advances in removing CO2) will have a major impact 30-60 years from now in reducing CO2 emissions and concentrations.   There will be advances that we can not even imagine now.

So consider what I am about to show as the worst case---and that the actual changes will not be so extreme.

Some Results

I will start by showing you the difference in conditions between a recent period (1970-1999) and two future periods (2030-2059, 2070-2099).    I show such thirty year periods to average out short-term variations that have little to do with climate trends. And I will present averages of the 12 climate runs.

Looking at the annual average of maximum temperatures, there will be roughly a 2C (about 3.6F) warming in maxima by 2030-2059--think 2045 (click on figures to enlarge).

But by the end of the century (2070-2099, think 2085), the average over the region will be twice that (around 4C increase, about 7F), with considerably more warming in the interior.

What about precipitation?  Looking to the first period (2030-2059), there is a generally small increase in precipitation, but there is something unexpected and subtle---decreases in precipitation in the downstream of some barriers.  An interesting finding to investigate further.

By the end of the century, the precipitation increases are more dramatic.   The Northwest will not dry out under global warming--we will generally get wetter.

Now, let me show you a plot of the annual mean temperatures from all ensemble members at a particular location (in this case Seattle).  Observed temperatures are shown with black dots.

The model runs are reasonably close to the observations before 2018, perhaps a degree too warm.  You will notice a steady rise over the century--nothing abrupt.  It appears that global warming might have contributed about a degree (C) of warming since 1970, with an additional 4C by the end of the century.

Summer precipitation at Seattle?  Lots of variability, but it looks like there will  be a small drying (perhaps 1 inch over the summer) by the end of the century.
Winter precipitation in Seattle?  A small increase, again with lots of year to year variability.

Want to see something scary?  Next, let's look at changes to our snowpack.

Here is the are the April 1 snowpack for 1970-1999, 2030-2049, and 2070-2099.  Modest declines over the lower-elevation terrain by mid-century.  Less change on the high terrain in British Columbia.  Much larger declines by the end of the century.  I don't think there will be skiing in Snoqualmie Pass in 2085 if the warming is not reduced.

Summer winds speed changes at the surface?  Generally weaker, except in the Strait of Juan de Fuca and Strait of Georgia.  Not good for wind generation.

The results I have shown you above are just the tip of the iceberg on what we can explore with these model runs.  Will cloudiness change?  How about the strong winds that drive wildfires?  There are many interesting questions that can be addressed with such climate simulations.

Major Lessons

The runs described above represent the best guidance now available for how global warming will influence our region if nothing is done to address greenhouse gas emissions.   By the end of the century, there will be substantial warming, with the average summer day around Puget Sound climbing into the mid-80s, rather that the upper 70s of today.  Our typical winter day west of the Cascades will have a high around 50F.   Cascades snowpack will decline substantially on April 1st (about 50% below today's value at 5000 ft). Winters will be wetter, but summers slightly drier (they are already typically dry today, but will be even more so under global warming).  Temperatures below freezing will become rare by the end of the century here in Seattle.  East of the Cascades, the influence of warming will be greater (see example for Yakima minimum temperatures below)

We are already seeing some small  temperatures impacts of global warming (1-2F), which implies that the major heat waves  TODAY are mainly natural variability (if temperatures is 20F above normal, as we observed earlier this month, roughly 18F of that warmth is natural).

Next Steps

There is much that should be done next.  First, we need to statistically improve our current runs, using bias correction based on the contemporary period. Next, we should run these simulations with an improved version of our modeling systems, using less aggressive and probably more modest global warming scenarios.  We should run our regional model driven by the next generation of global climate models (CMIP-6) and add physics variability and different start dates to get a wider range of solutions.

Unfortunately, our Amazon funds have been if you represent a foundation or a potential donor, and are interested in helping, please let me know or check here. 
Change in summer precipitation in inches

I believe simulations like those shown above will provide major assistance to a society that will have to adapt to a certain amount of climate change.  I also think that someone could make a good business out of providing regional climate prediction services.   But this not the kind of thing that the National Science Foundation would support (too applied) and the State of Washington doesn't support much outside climate research.

Sunday, June 23, 2019

Preparing for Wildfire Smoke

There is no smoke over the Northwest right now and the weather should be cool/wet later this week, so there is no imminent threat of smoke over the region.

But some fires in the region are inevitable, and thus some smoke should be expected, particularly east of the Cascade crest.  This blog will examine expectations for the coming wildfire season and talk about common sense preparation that can make one "smoke resilient" for a minimal investment.

The Current Situation

There are no major fires in the Northwest right now and air quality is good throughout the region.    In fact, there are fewer fires than normal burning at this time.  The Forest Service Observed Fire Danger map (below) suggests low potential for fire right now.

And as illustrated by the accumulated precipitation forecast through next Sunday morning (below), the next week should be on the wet side (and cool) across the Northwest, with particularly heavy rain over British Columbia and Alberta. 

This precipitation will delay fires in British Columbia (which was a big problem last year) and over eastern Oregon and SW Oregon.  Although the models are suggesting a return to more normal, warmer, drier conditions in early July, this wet period will sufficiently moisten the surface to push wildfire season into mid-July or beyond.

At this point, there is no reason to expect more wildfires than normal or a particularly smoky season in western WA.  I suspect that a repeat of last year's, two-day "smokestorm" is unlikely.   But some smoke over the region is nearly inevitable.

Reflections of last year's smoke

Smoke is unpleasant, but one needs to keep the "threat" in perspective.  Take last summer.   Although there was several weeks of smoky haze, most of the time the smoke stayed aloft above western Washington, with relatively clean air at the surface. 

To illustrate,  here is the concentration of small particles (PM2.5) in Seattle over summer 2018.   Most of the period was fine (under 20), but there was a period from roughly August 11-August 25th that was quite bad.  Also note the spike on July 4th!  So we are talking about a few weeks... no more.
Spokane?   They had one HUGE spike for a single day, and an extended period of moderate smoke that encompassed much of August.  They are closer to many of the fires than Seattle and don't enjoy as much of the clean air off the Pacific.  But still, much of the summer was fine (e.g., June and most of July).

Taking steps to get ready for smoke

The time to get ready for wildfire smoke is now--critical local supplies will be gone once air quality starts to decline. 

High-quality air filters can make a huge difference.

Last summer, I do some experiments using a cheap box fan, with a high quality furnace filter mounted on its intake side.   Professor Dan Jaffe at UW Bothell, an air quality expert, did the same.    The impacts were huge---this simple setup took most of the wildfire smoke out of the air.  We also found that without filtration, inside air wasn't much better than outside air.

Puget Sound Clean Air Agency did similar experiments (see below).

The key is to get a very good furnace filter (MERV 13 or FPR 10).     Yes, they cost more (about $20), but are worth it.

So if you have a house or apartment with a forced air system, get one of these good filters, and when there is smoke around, keep the system running 24 hours a day (most thermostats have fan settings).   And, close the windows if you can.  You will breath much better.

If you can't follow that approach, purchase a cheap box fan (they are about $20) and a 20" by 20" high-quality furnace filter, mounting the latter to the fan. (Puget Sound Clean Air agency provides instructions to do so) and there are several YouTube videos on the topic.

If you want to spend more money, you can buy commercial air purifies for $50-150.

Another possibility is stock up in a high quality filter mask, but be sure to get one that is at least N95 or N100.  But wearing such masks gets old, real fast.

Whatever approach you take, it is best to stock up now.  Last year, the stores were stripped of filters, fans, and masks as soon as the smoke started.  At my local food store, there is a huge pile of box fans available for purchase.

Better Smoke Prediction

There is one element of the smoke business that is radically changed compared to even five years ago:  highly skillful smoke models run by NOAA, Environment Canada, and others.  My favorite has been the NOAA/NWS HRRR smoke model (see below), which can give you warning a day in advance of smoky trouble. You can also use the output of such models to plan day trips to less smoky locations.

In short, there is much you can do to lessen exposure to wildfire smoke. 

Wildfire smoke has historically been a fixture of the region, and the unnatural suppression of fires has led to forests that burn catastrophically.  Better forest management and the return of regular fires (some from prescribed fires) will lead to an improved situation in the long-term, but some summer smoke should be expected each year.

Thursday, June 20, 2019

My Number One Weather Question Recently

During the past few months,  I have been getting a large number of emails, often with attached pictures of beautiful multi-color clouds (see below).

Courtesy of Lise Brandhagen

This picture is licensed under the Creative Commons License

These beautiful pastel colors are often found in thin middle and high clouds and are produced by a mechanism called iridescence. These are iridescent clouds and occasionally "rainbow clouds", although their origin are very different from real rainbows.  Such clouds have a large number of similarly sized cloud droplets or ice crystals and are frequently associated with altocumulus, cirrocumulus or lenticular clouds.

Picture courtesy of Mark Coates

Iridescence is produced by a physical mechanism called diffraction, which is associated with the wavelike nature of light. Light is bent around the corners of particles or through holes and gaps in them.  The amount of bending depends on the wavelength of light, with different colors having different wavelengths (shorter for purple and blue, longer for yellow and red).  These diffraction effect creates the colors you see.

Perhaps the most impressive iridescence occurs in lenticular clouds, with the look totally other worldly (see below).  No wonder some folks thought they were UFOs!

I should note that the diffraction mechanism in iridescent clouds is different than the way colors are produced in rainbows, which separate the colors when light is bent entering and leaving materials (like a prism).

Where did the term iridescence come from?  The technical term for the phenomenon is irisation, which in turn reflects that role of the greek goddess Iris, who was the goddess of rainbows.   She also delivered messages from the gods to mortals.

Finally, let me note that I appreciate the picture folks send me and enjoy answering your weather questions.   This blog is one of my major main tools for outreach and public education  (the other is KNKX) and your emails and pictures make it a two-way interaction--which makes it more fun and meaningful for all of us.