School Fire over the Northern Blue Mountains

06-07 Aug 2005

After a few weeks of hot and dry weather over the inland northwest, the fire season was beginning to swing into full gear. Of special interest was the "School Fire", located over the northern Blue Mountains or nearly 100 miles south of Spokane.

Although this fire was nearly 100 miles south of the Spokane area, its affects could be easily viewed across the southern celestial dome. The heat from the fire was sufficient to lift the air to great heights which resulted in the formation of a pyrocumulus cloud. A pyrocumulus cloud forms if there is enough moisture and atmospheric instability over the intense heat source. Although not common, these clouds can grow large enough to produce lightning and possibly some light precipitation.

The combination of smoke and moisture was detected by the Spokane radar as noted in the image composite to the right. The heights of the radar returns are denoted in pink for each slice of the radar scan. The bottom left panel detects some returns or echoes above 37,000 feet. Values this high are often associated with thunderstorms. Despite this fact, the local lightning detection network depicted no nearby cloud-to-ground lightning strikes.

The picture in the upper left corner shows some radar returns in excess of 40dBz (yellow pixels) at an elevation of 11,500 feet. These values are often sufficient for light precipitation reaching the ground, however the NWS office received no reports of ground precipitation.

The animation to the right is of the visible satellite imagery from approximately 500 pm until 630 PM At least four fires could be detected on this loop, although the North Fork Fire (near Yakima) was rather faint. Even from 22,300 feet above the earth, the School Fire looked very impressive. The smoke column from this fire exhibited obvious vertical development (notice occasional blue enhancement and shadows on the ground and downwind smoke shield). By the last frame in the animation, this plume had spread as far as the Prospect fire, or nearly 140 miles to the east.

So what did this column look like from the ground? Although the bulk of the plume skirted by Lewiston, a couple of webcam images gave some clue.

The left image, taken at 331 PM, showed little signs of smoke. However, by 511pm, the skies darkened and an ominous layer of black smoke was noted at the top of the picture. This smoke hung around through much of the evening and even as of 10 pm...a nearby weather sensor was still detecting a layer of smoke over Lewiston.
Images courtesy of KLEW-TV

The large School fire continued burning through the night of August 6th and into the morning of the 7th. By morning, the fire (combined with others in Montana) had spread a massive shield of smoke as far east as North Dakota. The image below is a high resolution picture captured by the same satellite utilized in the animation previously depicted above. The smoke shield is delineated by the green arrows.
Image courtesy of the National Weather Serivce's Satellite Services Division.