August 09, 2017

Believe it or Not! Wildfire Smoke Is Cooling the Northwest

Today was another warm day, with Sea-Tac hitting 91F and temperatures rising above 100F in the Columbia Basin of eastern WA (see map).

But do you know that our temperatures this week would have been much warmer this week if it weren't for the substantial smoke covering our region?  Smoke that predominantly came from British Columbia?  Believe it or not, the proof is at hand!

The plume of smoke above us has reduced the amount of solar radiation reaching the surface...thus producing less surface warming.

Why is that true?  Because the smoke particles both scatter some of the solar radiation back to space and absorbs some of the sun's rays, the latter causing the air higher up in the atmosphere to warm.  By either mechanism, less solar radiation reaches the surface.

  Here at the University of Washington, the amount of solar radiation reaching the sensors at the top of our building has been substantially reduced by the smoke:  the numbers are shown below, dropping from 25.37 on August 1 to around 19.15 MegaJoules per meter squared on August 5-6.  Roughly a 25% drop in solar radiation!

Radiation in MJoules per m2
7/31   26.80
8/1     25.37
8/2     23.22
8/3     22.55
8/4     23.33
8/5     19.19
8/6     19.14
8/7     21.09
9/8     22.62

OK, the amount of solar radiation is less, but how can we prove that it cooled us off? 

To explore this issue, I asked Jeff Baars, a research meteorologist in my department, to explore the smoke's impact by taking difference between the UW WRF model forecast for surface (2-meter) air temperature and observations.  The UW WRF model does not include the effects of smoke (we are working on it!), so the difference between our model forecast and reality should reveal the effects of smoke.   The expectation is that the model without smoke will be too warm...but by how much?

Here is the difference between the forecast (72h) and observed temperatures at Seattle-Tacoma Airport from 23 July through last night, for the forecasts valid at 5 PM each day.  The various colors are for different resolution UW WRF forecasts (36, 12, 4, and 1.3 km grid spacing).  Before the smoke reached our region the WRF model forecasts were quite good, with very small errors.  But after the smoke hit, the errors reached around 10F, with the model being too warm.   Implication:  the smoke cooled Sea-Tac by 10F on two days, and less amounts on others!

What about Bellingham, a location even closer to the smoke source in BC?    Wow... the cooling effect of the smoke reached 12-14F!

Portand?  The smoke took a bit longer to get down there, but when it did, the temperature effects were substantial (see graphic).  The model seems to be 2-3F too warm before the smoke hit, but when it did (August 7-8), the cooling effect was large (over 10F).

We did a similar analysis for 5 AM, when temperatures are near their daily low, and found little effect.  This is not unexpected:  much of the smoke is higher up, where the air is cooler and the smoke particles are relatively small compared to the wavelength of infrared radiation, which is the key player at night.

The smoke was substantial today and even worse this evening, something shown by the small particle concentration (PM2.5) at Seattle and Tacoma (see below from Puget Sound Clean Air Agency). Levels of 60-90 micrograms per cubic meter are unhealthy of vulnerable populations.   Weakened solar radiation coupled with cooler temperatures also means that there is less drying of the soil.

According to the Canadian smoke forecast modeling system, we have several more days of this.  And meteorologists need to get the effects of smoke into our weather forecast models, something that is generally missing.

So should we thanks the Canadians for keeping us cool, or curse them for smoking us out?  I will leave that for you to decide.


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.  No remote access...sorry.


  1. One hazards to ask if these findings will lend support for one of the various schemes (e.g. spraying ocean water into the air, sulfur dioxide, even something to do with 'diamond dust'?) to counter global warming by intentionally altering the atmosphere?

  2. If you spray ocean water into the air on large scales far from the sea, you add a large amount of salt to the top layer of the soil as the water evaporates. That's probably not a good idea should you care about the local plant life, including agriculture.

    Sulfur dioxide is worse. Spray that into the atmosphere and it combines with water vapor and oxygen to create sulfuric acid, i.e. acid rain. Diesel fuel has been cleaned of its sulfur content at great expense specifically to combat this problem. I'll also note that sulfuric acid rain occurs on the hellscape of planet Venus.

    So no, there's not much we can or should do to try to prevent solar radiation from hitting the ground. The best ways to curb solar heating are to put solar collectors on the ground that convert a portion of incident sunlight into useful energy so that it doesn't heat the ground instead. The two classic examples here are plants and photovoltaic cells.

  3. I would rather have the heat than dangerous particles in my lungs. Several are reporting problems breathing this smoke. My sinuses are plugged from it!

    From Suquamish, Seattle is totally lost in the haze. We also can't see the Olympics unless one goes about 10 miles west of the Hood Canal Bridge.

    Cliff, will you post on the expected eclipse weather? Many who are traveling to see it on the night before are finalizing their eclipse strategies. I personally have written off eastern Oregon as too crowded, and too hazy perhaps even with this new weather coming in. That area west of Salem is looking good now and I am also recommending people sacrifice a few seconds of totality by staying 5-10 miles north or south of the centerline. More convenient for making an escape soon afterwards.

  4. Kenna, if you want to see the eclipse, there is no "finalizing" your eclipse strategy 11 days out. Stay where you are going to stay, but be mobile in the pre-dawn darkness of the 21st and go where you must based upon the 12 hr forecast.

    Until this smoke clears, we have two huge variables to deal with, not just one.

  5. I was looking at the air temperatures on the PS Clean Air website and noticed the large temperature inversion in the area the other day. I wonder if that is the smoke particles holding the heat at that higher altitude at night as well. I noticed that the temperature at 700m was over 3C warmer than the surface on Tuesday morning. That's a pretty big inversion.

  6. i'll much rather have warmer clean air than have to breathe in the toxic smoke...

    Canada really needs to do something about their forest fires or this would be a yearly recurring event.

  7. Dan, I am herding a bunch of paleontologists from as far away as Japan - so I have to strategize and plan. I know others who are planning between eastern Oregon and western Oregon. It would be helpful to have long range information so as to weigh one or the other.

  8. I've canceled my OR trip entirely after reading all the dire warnings about traffic... we will have something like 91% coverage here anyway. I decided driving down to the Salem/Corvallis area is just not practical unless you're making a 3 day trip of it.

    As for the Canadians "doing something" about the forest fires -- wildfires are a natural event. The way to have fewer, smaller fires is probably to let them burn, as they were meant to.

  9. I wish those commenting here regularly about how awful the smoke is would spend just a day or two in the Midwest in the city environs on a usually hot summer day, with temps hitting 95 and humidity off the charts, with the additional miseries of the "heat island effect" thrown in for good measure. Couple all of that with large amounts of car and truck exhaust, THAT is what's called poor air quality. This air doesn't hold a candle to that element.

  10. Jayemarr, I think that's unnecessarily defeatist. If you east over Snoqualmie Pass at midnight, continue through the Tri-Cities to Pendleton, then take 395 south to John Day, you might have wonderful results there.

    A 91% partial eclipse is less than 5% as spectacular as a 100% total eclipse. Don't give up.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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