Tornadoes are classified by the National Weather Service using a rating scale from zero to five, based on the damage they cause according to the Enhanced Fujita Scale. This scale, named after Dr. Ted Fujita, was created to estimate wind speeds based on the type and amount of damage caused by tornadoes. In 2007, the Enhanced Fujita Scale (EF0 to EF5) was introduced by a team of experts to enhance the accuracy of wind speed estimates.
The EF Scale considers various factors and provides a more precise estimate of wind speed based on storm damage compared to the original F-Scale. It assesses 28 damage indicators such as trees, building types, and structures to determine the level of damage, ranging from visible damage to complete destruction. Unlike the original F Scale, the EF Scale takes these factors into consideration. Both scales have been used to rate tornadoes since 1971.
Following a tornado, the NWS dispatches meteorologists to conduct ground surveys in cases of significant damage, injuries, or deaths, or when populated areas are affected. For weaker tornadoes causing minimal damage or believed to be short-lived, the NWS relies on photos, storm spotter reports, and chaser reports to estimate the Enhanced Fujita rating.
For major tornado events, experienced survey experts, wind engineers, and aerial surveys may be employed to assess the path and extent of damage. The time taken to rate a tornado varies based on factors like the number and strength of tornadoes, their length, and geographic coverage. Typically, the NWS aims to complete storm surveys promptly, usually within a day or two, but in the case of larger outbreaks, it may take several days to finalize ratings and reports.
Getting an accurate tornado rating involves analyzing data gathered in the field, and can be expedited with initial visuals like photographs or live video. However, determining a precise rating from visuals alone can be challenging. The Enhanced Fujita Scale provides a range of damage assessments corresponding to different tornado ratings.
