Monday, 4 October 2004
One of the major challenges in the operational and research severe weather communities is warning validation. It is well known that not all large hail, damaging winds and (weak) tornado occurrences are documented, creating gaps in the record which distort both climatology and forecast verification statistics. Forensic investigations are frequently involved with the reconstruction of severe weather events relevant to litigation. This paper reports on one such study, the outcome of which is documentation of an apparent F1 tornado unreported in Storm Data or other databases. The opposing side in the litigation argued strenuously that the multi-million dollar loss of a large warehouse roofing system was the result of poor design or installation causing failure during a weak (<55 mph) downburst. The insurers, on the other hand, were of the belief that a tornado must have accounted for the damage. As a result of the discovery process leading to a potential trial, a considerable amount of information was collected allowing for the creation of a rather comprehensive damage assessment. Resources included aerial photographs, numerous eyewitness accounts (through depositions) and damage reports from local newspapers, police, utility and fire departments. On the early afternoon and evening of 27 June 1995, numerous, though short-lived, severe thunderstorms erupted within a cold-core circulation drifting over northern Illinois and Indiana. Several confirmed funnel clouds and tornadoes were reported in this region. One of the intense thunderstorms passed over Munster, IN. Doppler radar winds suggested surface wind gusts were generally restricted to 55 mph or less. However, a 3-D correlated shear embedded the storm persisted for 45 minutes as it passed over the area. Around 6:20 PM CDT, an eye-witness, whose work place adjacent to the warehouse was damaged, reported a dark cloud along with a vortex a turny looking thing with a bunch of debris in it A reconstruction of the damage path indicates it was confined to 100-300 yards in width and extended for about 1.5 miles. The sporadic nature of the damage suggested one or more suction vortices. The damage path, which ran almost parallel to advancing gust front, curved inwards towards the cyclonic circulation of the parent storm. Aside from the removal of a large swath of the warehouse roof, impacts included large (>2 inch) river rock being hurled through the air, overturned trailers and delivery trucks, debris carried more than a half mile, heavy VAC equipment being uplifted and removed from roofs, damage to other roofs and small trees being uprooted and tossed. We believe the evidence compiled is consistent with a short lived F1 tornado. Given the extent of litigation endemic in the U.S. today, can we suggest that there may be other tornado, large hail or damaging wind investigations which have uncovered incidents which could help to extend the severe weather climatological record?
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