May 17, 2019

How tornadoes are measured

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.

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In photos: Authorities issue warning as Americans venture out for Memorial Day weekend

Venice Beach in Los Angeles on May 24. Photo: David McNew/Getty Images

Authorities urged Americans to maintain social distancing and wear masks against the coronavirus amid reports of packed beaches and bars during the Memorial Day weekend.

Driving the news: Law enforcement stepped up beach patrols, authorities on Florida's Gulf Coast closed parking lots because they were full and there were crowded scenes at Lake of the Ozarks bars in Missouri, per AP, which reports a shooting injured several people at a packed Daytona Beach in Florida.

Coronavirus dashboard

Illustration: Aïda Amer/Axios

  1. Global: Total confirmed cases as of 9:30 p.m. ET: 5,405,029 — Total deaths: 344,997 — Total recoveries — 2,168,408Map.
  2. U.S.: Total confirmed cases as of 9:30 p.m. ET: 1,642,021 — Total deaths: 97,698 — Total recoveries: 366,736 — Total tested: 14,163,195Map.
  3. World: White House announces travel restrictions on Brazil, coronavirus hotspot in Southern Hemisphere Over 100 coronavirus cases in Germany tied to single day of church services — Boris Johnson backs top aide amid reports that he broke U.K. lockdown while exhibiting symptoms.
  4. Public health: Officials are urging Americans to wear masks headed into Memorial Day weekend Report finds "little evidence" coronavirus under control in most statesHurricanes, wildfires, the flu could strain COVID-19 response
  5. Economy: White House economic adviser Kevin Hassett says it's possible the unemployment rate could still be in double digits by November's election — Public employees brace for layoffs.
  6. Federal government: Trump attacks a Columbia University study that suggests earlier lockdown could have saved 36,000 American lives.
  7. What should I do? Hydroxychloroquine questions answeredTraveling, asthma, dishes, disinfectants and being contagiousMasks, lending books and self-isolatingExercise, laundry, what counts as soap — Pets, moving and personal healthAnswers about the virus from Axios expertsWhat to know about social distancingHow to minimize your risk.
  8. Other resources: CDC on how to avoid the virus, what to do if you get it, the right mask to wear.

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Updated 1 hour ago - Politics & Policy

Republicans sue California over mail-out ballot plan

California Gov. Gavin Newsom during a February news conference in Sacramento, California. Photo: Justin Sullivan/Getty Images

President Trump accused Democrats of trying "Rig" November's general election as Republican groups filed a lawsuit against California Sunday in an attempt to stop Gov. Gavin Newsom (D) from mailing ballots to all registered voters.

Driving the news: Newsom signed an executive order this month in response to the coronavirus pandemic ensuring that all registered voters in the state receive a mail-in ballot.