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.
Key differences in damage indicators between EF4 & EF5 (from Marshall et al. 2007):
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