As noted in the news article I linked above, this fire (known now as the 'Big Hump Fire') started last Thursday, but has really grown this week. They also note in the article that we haven't had any lightning recently so...they assume the fire was manmade somehow.
We can see the smoke from the fire on Tuesday's high-resolution MODIS imagery:
|MODIS image from the Aqua satellite on Tuesday, Sept. 6, 2011.|
So, where is the smoke from this fire going to go? We can once again use NOAA HYSPLIT trajectory model to look at smoke plume trajectories over the next 24 hours. This model is freely available and you can run your own simulations using it online at http://ready.arl.noaa.gov/HYSPLIT_traj.php.
|NOAA HYSPLIT model forecast trajectories for 24 hours starting at 12Z, Sept. 8, 2011.|
|UW 4km WRF 12-hour forecast of 850mb winds (barbs), temperature (colors) and heights (contours) valid 00Z, Sept. 9, 2011.|
But let's return to the trajectory model above. The lower panel of the graphic above shows a time-height series for the plumes. Time increases as you go to the right, and each star represents a time when the model started another plume trajectory calculation--every three hours. You can see how high above the ground each of the plumes gets by following the lines that come out of those stars.
Notice that for plumes starting or already traveling during the mid to late afternoon (from about 18Z through 00Z), the plumes get pretty high--up to 1000 meters above the ground. But then, once we get to the evening (after 00Z), the plumes stop getting that high--they get trapped very low near the ground. This continues until the following day in the afternoon, when once again the plumes are able to rise higher.
This shows the effect of the nocturnal inversion extremely well (at least, in this model). Remember from my discussions about diurnal cycles and about the nocturnal boundary layer wind maximum that at night the land surface cools off very rapidly. This, in turn, causes the air close to the surface to cool more than the air above it. The result is a layer at the surface where temperature increases with height--a stable "inversion". Stable layers inhibit vertical motion. Thus, at night, we can see that the stable layer that has formed near the surface is keeping the smoke plume low to the ground--it can't rise up.
In contrast, during the afternoon when the sun is beating down, the ground surface warms up very quickly. Similarly, the air near the surface warms faster than the air above. This leads to a layer near the surface where the temperature decreases with height--a more unstable layer. The more unstable the layer, the more easily you can have vertical motion. We see that in these smoke plume trajectories--the smoke rises much higher during the afternoon when the near-surface layer becomes less stable (and we get more convective mixing).
As I noted in my last blog post, the Pacific Northwest will be stuck under a ridge for the next several days, with warm temperatures and low humidities persisting.
|UW 4km WRF 72-hour forecast of surface dewpoint temperature valid 12Z, Sun., Sept. 11, 2011.|
One slightly positive effect of this wildfire is that its smoke can contribute to some absolutely amazing sunsets. Below is a screen capture from Dr. Dale Ireland's high-definition webcam that was pointing in the direction of the fire as the sun went down on Tuesday evening.
|Image from Dr. Dale Ireland's page.|