□ The Elie tornado of June 22, 2007, was a severe weather fanatic’s treat. Unlike most violent tornadoes, the Elie storm was slow-moving, clearly visible and exceptionally small, which provided photographers ample opportunity to document the rope-like funnel from close proximity. The event remains the most recent F5 tornado on the now semi-outdated Fujita scale. Several months passed before authorities at Environment Canada upgraded the tornado from an F4 to an F5. Many suspected the upgrade was motivated more by a sense of novelty than objectivity. Footage of the tornado and a close review of the damage survey, however, indicate that the F5 rating was appropriate.
The Elie tornado developed under unusual circumstances. It was spawned from a low precipitation supercell that had very little falling rain or hail. Unlike most violent tornadoes, the storm travelled generally to the southeast and executed several counterclockwise loops as it tore through fields south of the Trans-Canada Highway (McCarthy et al., 2007). From beginning to end, the tornado travelled only four miles. When the tornado’s meandering motion is taken into account, the total path length was closer to eight miles.
The storm expanded to approximately 150 yards in width during its mature stage, but failed to strike any buildings while at maximum size. After roping out, the tornado passed directly over four homes on Elie Street after narrowing to around 35 yards in width. Surveyors initially believed that the tornado moved over the row of houses from the northwest, but it was later shown that the storm struck the area while completing a counterclockwise loop after stalling in a field to the south (McCarthy et al., 2007).
The severity of the damage was indicative of F5 intensity, but surveyors were hesitant to award the tornado an F5 rating due, in part, to its slow forward motion. Analysis of a video (referred to as the “Hutterite” footage in the survey report) shot from the Trans-Canada Highway, however, indicated that the tornado spent no more than 30 seconds atop each house (McCarthy et al., 2007). Additionally, the video revealed that the tornado:
a) Ripped an entire frame home from its anchorage and hurled it through the air.
b) Lifted a 3/4 ton GM van high into the air and centrifuged it out of the funnel at a high rate of speed. The van was thrown 150 yards in one toss before bouncing an additional 15 yards, finally coming to rest in a mangled state in a field to the south (commences at :11 in the clip below).
c) Rotated in a manner consistent with winds well over 200mph.
The damage caused by the Elie tornado with determined F-scale values next to each property is shown above. The home swept clean from its foundation in the upper right corner was the basis of the F5 rating. The home was found to have been well-constructed and bolted to its foundation. The house beneath it was completely destroyed except for a section around the fireplace. The empty basement at center is the remains of the home that was filmed being lofted into the air. The house was of decent but questionable construction, so the damage was deemed to be of low-end F4 intensity. At bottom is a very well-constructed home that received damage categorized as upper F2 or lower F3 intensity. The extremely narrow tornado swept part of the house away, exposing the foundation underneath.
An interesting feature of the Elie tornado was its appearance while at F5 intensity. The tornado was near the end of its life and appeared to be in its decaying stage when the extreme damage occurred. The funnel had lost consistent contact with the ground and was spinning and reforming above a narrow core of extreme winds. The shrinking of the tornado’s wind field may have caused the rotation to rapidly accelerate for a brief period of time. Crude photogrammetry of the debris motion (assuming the funnel is 35 yards in diameter and using a 0.5 second time interval) indicates visible winds over 250mph. The well-known Pampa, Texas, tornado of 1995 was similar in many ways to the Elie event. The Pampa tornado was a bit wider than its Canadian sister, but both tornadoes moved very slowly, both had drill-shaped bases and wide debris fields and both were extremely violent. Tom Grazulis’ photogrammetry of the Pampa event indicated ground level winds were around 300 mph (Grazulis, 2001).
The Elie event proves that the size and shape of tornadoes is often unrelated to overall intensity. Additionally, the unremarkable appearance of the storm suggests that potentially dozens of tornadoes capable of causing EF5 damage occur each year with little notice.