Mike Fromm of NRL has sent out the following little pearl on the pyroCb listserve (you may have to have a Yahoo account to see the listserve... account is free).
"If you have 9 minutes to spare, and don't mind a little salty language, check out the Youtube video below.This happens to show the Milford Flat fire (Utah, 7 July 2007) precisely when it was in early pyroCb stage.
For newcomers to this group, and to refresh others' memories, Milford Flat was noteworthy for a number of
reasons:
* It was burning in grass and sagebrush
* It had started just one day before
* It was the largest fire in UT history
* 2 people died in a car/motorcycle accident near the firestorm (you will see how this might have occurred)
* stratospheric smoke was from this event was detected by Tom Duck's Dalhousie lidar, CALIPSO, and NASA's DC8.The video is notable for the absolute blackness under the cloud/plume. We're taking votes on the optical depth:)"
The video ends abruptly but in checking, the folks in the video were not hurt but must have been rightly scared.
On the Smog Blog, we did see the high optical depth from this plume archived in July 2007 but did not identify this particular fire. Optical depths were clearly > 1.0 over a wide area and showed up as cloud.
I'll take Mike's challenge and I would guess that the optical depth is >6 with single scatter albedo of <0.6. The reason I say this is that clouds can have optical depths of >30 but you still see scattered light through them. This is because they are largely scatterers not absorbers. But in this smoke plume, an optical depth of 6 with >40% absorption will eat up all the photons before they hit the ground. This is a great video.