How do scientists tell how strong a tornado was?
Wind is invisible, and a tornado can be narrow and over quickly. So after one has passed, how do weather scientists decide how strong it was? They work like detectives โ and their main clue is what the tornado left behind.
NOAAโs National Severe Storms Laboratory describes a tornado as โa narrow, violently rotating column of air that extends from a thunderstorm to the ground.โ You often cannot see the air itself: โBecause wind is invisible, it is hard to see a tornado unless it forms a condensation funnel made up of water droplets, dust and debris.โ So to rate a tornado, the lab explains, โexperts examine the damage it caused. From this information, we can estimate the wind speeds.โ
Basis: NOAA National Severe Storms Laboratory, โSevere Weather 101: Tornado Basics.โ Quotations unchanged.
The ruler they use is called the Enhanced Fujita Scale, or EF-Scale. It โwas implemented by the National Weather Service in 2007 to rate tornadoes in a more consistent and accurate manner.โ The detectives first ask what was hit: the scale uses โ28 damage indicators such as building type, structures and trees.โ Then they ask how badly: โFor each damage indicator, there are 8 degrees of damage ranging from the beginning of visible damage to complete destruction of the damage indicator.โ Putting the two answers together gives an estimate of the wind โ and a rating.
Basis: NOAA National Severe Storms Laboratory, โSevere Weather 101: Tornado Basics.โ Quotations unchanged.
Older tornadoes were rated on the original Fujita Scale, and scientists did not throw those records away. โThe original F-Scale historical data base will not change. An F5 tornado rated years ago is still an F5,โ though its winds โmay have been somewhat less than previously estimated.โ And here is a surprise: even the experts say they are still working out how tornadoes start. โHow do tornadoes form? The truth is that we don't fully understand.โ โWe still have lots of work to do.โ
Basis: NOAA National Severe Storms Laboratory, โSevere Weather 101: Tornado Basics.โ Quotations unchanged.
Here is a puzzle to think about โ a guess, not a finding from the source: if the rating comes from damage, what happens when a tornado crosses an empty field with no buildings and few trees? There may be very little left to examine, so its rating might come out lower than the winds it really had. Can you think of other clues scientists could use when there is nothing to damage?
โป A hypothesis is an idea that isn't proven yet.
๐ Sources for the rankings mentioned in this note (links to the original data and retrieval dates) are on each quiz page below.