TULSA - Next time you're watching television and a chaser yells, "Tornado on the ground. It's an EF3!" know that it is nothing more than his/her estimation.
Often over estimated, the official classification may not be known for several days.
After skies clear, but before debris is cleared, the National Weather Service sends trained meteorologists to comb through the damage.
They look for very specific damage indicators, and after close examination they rate the damage, noting the width and length of the track of the storm. But it wasn't always this way.
The original scale to rate the damage was called the Fujita - Pearson Tornado Scale, named after Tetsuya "Ted" Fujita and Allen Pearson. Fujita's original scale went from (F0 -F12) with F12 being Mach 1. He intended F0-F5 be used in practice, but did describe an F6 tornado as "inconceivable."
Here is the Fujita Scale used from 1971 to 2007:
F0 winds less than 73 mph
F1 73-112 mph
F2 113-157 mph
F3 158-206 mph
F4 207-260 mph
F5 261-318 mph
There were problems with the original scale.
When there were no structures in the path of the storm, it was difficult to estimate the damage that may have occurred. This led to inconsistent ratings of tornadoes, and in some cases, an overestimate of tornado wind speeds.
Because of this, a panel of meteorologists, structural engineers, and other experts in the field began working on an improved rating system. What they came up with and became the new standard was the Enhanced Fujita scale (EF), started in February 2007.
They use specific damage indicators (DI) and degrees of damage (DOD) to better identify the wind damage and rate the tornado. Some of the damage indicators are single-wide mobile homes and small retail buildings such as fast food restaurants. There is a differentiation between damage to a softwood tree and a hardwood tree.
There were procedures outlined so that there would be some consistency:
Conduct an aerial survey of damage path to identify applicable damage indicators and define the extent of the damage path
Identify DI's that tend to indicate the highest wind speed within the damage path
Locate those DI's within the damage path
Conduct a ground survey and carefully examine the DI's of interest
Follow the steps outlined for assigning EF-Scale rating to individual DI's and document the results
Consider the estimated wind speeds of several DI's, if available, and arrive at an integrated EF-Scale rating for the tornado event
Record the basis for assigning an EF-Scale rating to the tornado event
Record other pertinent data relating to the tornado event
The existing EF scale estimates the strongest wind gusts that occur 10 meters above the ground.
EF0 65-85 mph
EF1 86-110 mph
EF2 111-135 mph
EF3 136-165 mph
EF4 166-200 mph
EF5 over 200 mph
Some speculated that the lower wind speeds would lead to many more EF3 - EF5 tornadoes. Few would argue the recent tornadoes have been significant on either scale.
No matter how you rate them, the recent tornadoes have been very destructive, deadly, and historic. Honestly, after a tornado claims a life, it is of little consequence what number it is assigned.
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Severe Weather Safety
Tornadoes are Mother Nature's most violent storms. They can produce winds that can reach 300 miles per hour, and they can produce damage paths as wide as a mile and as long as 50 miles.
Another storm season is here, and that means it's time to make sure you and your family are ready for the storms that will head our way.
What you need to do to prepare before the a thunderstorm, how to stay safe during the storm and then once the storm passes what you need to know.