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Firestorm Induced Tornado

by John Weaver and Dan Bikos

The video clips shown were supplied by Lt. Daniel Lee Bender of the LaPlata county Colorado sheriff's office.

The Missionary Ridge fire near Durango, Colorado initiated on the afternoon of June 9, 2002. By June 17 the fire had consumed 26,700 acres and had moved into an area of rich dry fuels. A red flag warning was in effect for the whole state. The 00:00 UTC sounding from Grand Junction, CO shows a dry adiabatic lapse rate from the surface to near 450 mb with winds from the surface to 700 mb 10 to 20 knots from the west / southwest.

A map of the area shows Vallecito reservoir which was mostly a dry lake bed at this time. LaPlata county fire responders were videotaping a fire northwest of the reservoir from a ridge line to the southeast. As the video sequences begin the area is still experiencing light and variable surface winds. Shortly thereafter, the winds mixed down and changed from light northerly to southwest at 10-15 kt. This windshift can be seen in this video clip

Following the shift in the winds, the fire began to burn much more vigorously. The visible satellite loop shows the plume expanding dramatically northeast of Durango (DRO) and the channel 2 (3.9 micron) loop shows how rapidly the burning area expands. At this point the fire grew substantially and the plume altered the mesoscale flow. A convergence boundary setup northeast of the flow and "landspouts" began to form over the dry lake bed. The first of these can be seen in this video clip.

The inflow on the north side of the storm continued to increase in intensity as indicated in this video clip. This resulted in even more intense vortices along the convergence zone.

At this point the extremely violent updraft combined with the storm induced shear began to form a mesocyclone on the southwest flank of the fire plume. A rotating wall cloud like structure began lowering to the ground. Subsequent damage survey found F3-like damage to trees in the area. This damage estimate may be biased since the wood in the trees was extremely dry due to drought and heat from the fire. This feature can be seen in its entirety in this video clip. As another option this can be downloaded in two smaller segments. segment 1 and segment 2. At times small fire vortices were drawn into the main circulation resulting in burned automobiles found amongst unburned but wind damaged vehicles. Here is short clip of one of these vortices.

Following a brief dissipation the wall cloud like structure reformed becoming even more well-defined than earlier.

The winds outside of the plume affected region continued to be southwesterly at 10-15 knots. However, in the vicinity of the mesoscale rotation an apparent RFD developed and wind speeds began gusting in excess of 30 knots (estimated by personnel on scene). A very large gustnado formed in the center of the dry lake bed.

The following clip shows tree damage on the affected hillside. The last clip shows vehicles with windows blown out and camper trailers overturned in the dry lake bed. It also shows 2 of the vehicles burned by the embedded fire vortices.