When a tornado occurs, trees will tend to fall in varying direction rather than in a straight line. The trees will show torque, spin, in their pattern of damage. Also the overall force which causes a building collapse, or windows to blow out, roofs to blow off would all suggest a tornado.
However if the damage fell in a straight line which indicates a downburst or microburst for a thunderstorm cell. The winds were oriented in a straight line. During surveys, the National Weather Service will even examine blades of grass to see if the grass was bent in different directions.
Tree damage from a downburst
Thunderstorm forming over Lusk by B.Keagen of Casper,Wyoming
Of course photographs and eye-witness noticing of funnels is the surest way of making a determination, but in our part of the country, the funnels are often shrouded in heavy rain. We don't get to see it.
A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to, but distinguishable from, tornadoes which generally have convergent damage.(wiki)
But there is really nothing "Micro" in terms of damage from a microburst or straight-line winds which can reach speeds in excess of 100 mph!
Below listed the scale of tornado damage,the scale was enhanced in 2007, with rankings running from EF (Enhanced Fujita) - 0 through 5. The ratings are based on the amount and type of wind damage.
The ratings are:
EF-0. Light damage
Wind 65 to 85 mph. Causes some damage to siding and shingles
EF-1. Moderate damage
Wind 86 to 110 mph. Considerable roof damage. Winds can uproot trees and overturn single-wide mobile homes. Flagpoles bend.
EF-2. Considerable damage
Wind 111 to 135 mph. Most single-wide mobile homes destroyed. Permanent homes can shift off foundation. Flagpoles collapse. Softwood trees debarked.
EF-3. Severe damage
Wind 136 to 165 mph. Hardwood trees debarked. All but small portions of houses destroyed.
EF-4. Devastating damage
Wind 166 to 200 mph. Complete destruction of well-built residences, large sections of school buildings.
EF-5. Incredible damage
Wind above 200 mph. Significant structural deformation of mid- and high-rise buildings.
Katina / Katrina Hurricane is EF 4 with 175 mph (280 km/h)
Flooded I-10/I-610/West End Blvd interchange and surrounding area of northwest New Orleans and Metairie, Louisiana
More Toronto and Hurricane captures Check out:
10 Most Damaging Tornado of All Time
How Tornado hit the Cars (video)
