EF Ratings
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How is an EF Rating determined?
How is an EF Rating determined?
NWS personnel walk through the damage and determine the wind speeds that produced the damage at each home, barn, office, etc.
Often, architects and engineers participate too.
The wind speed then determines the EF rating.
MUST determine the wind speed first!
No damage = no rating possible
EF Ratings
EF Ratings
Idealized
Idealized
EF Ratings
EF Ratings
Real-World
Real-World
Example: Moore, OK, 5/3/99
Example: Moore, OK, 5/3/99
At this particular house:
Roof is completely gone
Most of the exterior walls are blown down - just one small piece, next to the tree, is still standing
Most of the interior walls, except for one on the left, also appear to be blown down
These winds are probably in the 150-165 mph range
Further down the street...
Further down the street...
Scroll through the images to the right
What does that mean?
What does that mean?
Experts will walk through the entire damage area and examine as many structures as possible.
The maximum, worst damage, is what determines the final EF rating.
Example of How to Use Damage to Estimate Tornado Wind Speed
Example of How to Use Damage to Estimate Tornado Wind Speed
Table of wind speeds associated with different levels of damage to a typical single-family home.
Key differences in damage indicators between EF4 & EF5 (from Marshall et al. 2007):
"An EF-4 rating was given to those homes that had all walls down and a pile of debris remaining on their foundation. EF-5 ratings were given to anchored homes that were swept clean from their foundations."
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