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Damage from the aftermath of a tornado that hit Alabama in March 2019. Photo: Elijah Nouvelage/Getty Images

Since February 2007, the National Weather Service has used the Enhanced Fujita Scale to measure the intensity of tornadoes. After the tornado strikes, meteorologists survey the damage it caused and assign a "rating" based on estimated wind speeds corresponding with the damage.

The backdrop: The EF scale is an updated version of the Fujita Scale, which was first introduced in 1971. The enhanced scale takes into consideration how winds affect certain types of structures in the tornado's path. It looks at how those structures are designed and how the design might impact the destruction they face.

Details: When damage from a tornado is assessed, NWS uses a list of "damage indicators" and "degrees of damage" to estimate likely wind speeds and then assigns the tornado a rating between EF-0 to EF-5.

  • Per the NWS website, the goal is to "assign an EF Scale category based on the highest wind speed that occurred within the damage path."

The scale:

  • EF-0: 65-85 mph (Light damage)
  • EF-1: 86-110 mph (Moderate damage)
  • EF-2: 111-135 mph (Considerable damage)
  • EF-3: 136-165 mph (Severe damage)
  • EF-4: 166-200 mph (Devastating damage)
  • EF-5: Over 200 mph (Incredible damage)

How it works: First, the NWS will assess a variety of structures impacted by the tornado. Each structure, or damage indicator, has its own list of degrees of damage, which helps an evaluator determine a range of wind speeds and whether it is higher or lower than expected. This process is done for several structures before the overall tornado is rated.

  • For example, damage indicator 1 is "small barns, farm outbuildings" and damage indicator 2 is "one- or two-family residences." Other damage indicators include "motel," "strip mall," "school - 1-story elementary" and "tree-softwood."
    • Each damage indicator includes a description of its typical construction (to ensure a structure is being classified correctly).
  • Each damage indicator also has specific degrees of damage.
  • Oftentimes, NWS experts will conduct aerial surveys of the tornado-affected region to get an overview of the damage path as well.

Go deeper:

Go deeper

Updated 7 hours ago - World

Mexican President López Obrador tests positive for coronavirus

Mexico's President Andrés Manuel López Obrador during a press conference at National Palace in Mexico City, Mexico, on Wednesday. Photo: Ismael Rosas/Eyepix Group/Barcroft Media via Getty Images

Mexican President Andrés Manuel López Obrador announced Sunday evening that he's tested positive for COVID-19.

Driving the news: López Obrador tweeted that he has mild symptoms and is receiving medical treatment. "As always, I am optimistic," he added. "We will all move forward."

7 hours ago - Politics & Policy

Sarah Huckabee Sanders to run for governor of Arkansas

Sarah Huckabee Sanders at FOX News' studios in New York City in 2019. Photo: Steven Ferdman/Getty Images

Former White House press secretary Sarah Huckabee Sanders will announce Monday that she's running for governor of Arkansas.

The big picture: Sanders was touted as a contender after it was announced she was leaving the Trump administration in June 2019. Then-President Trump tweeted he hoped she would run for governor, adding "she would be fantastic." Sanders is "seen as leader in the polls" in the Republican state, notes the Washington Post's Josh Dawsey, who first reported the news.

Coronavirus has inflamed global inequality

Illustration: Aïda Amer/Axios

History will likely remember the pandemic as the "first time since records began that inequality rose in virtually every country on earth at the same time." That's the verdict from Oxfam's inequality report covering the year 2020 — a terrible year that hit the poorest, hardest across the planet.

Why it matters: The world's poorest were already in a race against time, facing down an existential risk in the form of global climate change. The coronavirus pandemic could set global poverty reduction back as much as a full decade, according to the World Bank.