Stay Informed: How Scales Help Us Describe Disasters

Photo of palm trees bending in gale force winds

Last year’s Atlantic hurricane season was record-breaking. There were 30 named storms during the 2020 season. Thirteen of those became hurricanes (top winds of 74 mph or greater). Six of those reached Category 3 or higher.(1)

Hurricanes are categorized using the Saffir-Simpson Hurricane Wind Scale. Other scales are used by experts to explain and describe the intensity or severity of disasters like tornadoes and earthquakes. Below are descriptions of some of them.

The Saffir-Simpson Hurricane Wind Scale

The Saffir-Simpson Hurricane Wind Scale was created in 1971 by civil engineer Herbert Saffir and meteorologist Robert Simpson. Hurricanes are rated (or categorized) 1 to 5 based on their maximum sustained wind speed. The category relates wind speed to the kinds of property damage that are likely to occur from wind.(2)

All hurricanes produce life-threatening winds, but only storms rated Category 3 and higher are considered major hurricanes. Major hurricanes cause devastating to catastrophic wind damage.Hurricane evacuation sign

Hurricanes of all categories can produce storm surge that requires people to evacuate and take other preventative measures.

The Saffir-Simpson scale only provides information about wind damage. It does not describe damage from other hazards, such as storm surge, inland flooding, or tornadoes spawned by the storm.

Along the coast, storm surge is often the greatest threat to life and property from a hurricane. At least 1,500 people died during Hurricane Katrina in 2005. Many of those deaths are attributed either directly or indirectly to storm surge.(3)

Evacuation orders are more likely to be based on storm surge or inland flooding than on the Saffir-Simpson category. It is critical for emergency officials and the public to stay informed of the forecast and to prepare regardless of whether they live near the coast or well inland.

Learn ways to prepare for hurricanes.

The Enhanced Fujita Scale

Researcher Ted Fujita and Allen Pearson of the National Weather Service (NWS), introduced the original Fujita Scale for rating tornadoes in 1971.

Wind researchers and engineers provided substantial enhancements to the scale in the early 2000s, called the Enhanced Fujita (EF) Scale. NWS adopted the scale in 2007. Like the F-Scale, the EF Scale estimates a tornado’s intensity on a scale, from 0 to 5, based on surveyed damage.(4)

Photo of person in the foreground of residential tornado destruction
Photo credit: FEMA

NWS is the only federal agency with the authority to provide official ratings for tornadoes. Ratings are not based on actual measurements of wind speed; although, some researchers have equipment that can estimate speeds through radar velocity data. Ratings are estimates of wind speed based on assessed damage to structures and vegetation. The result is a range of likely
wind speeds.

The most recent EF5 tornado struck Moore, Okla., in May 2013.(5) It killed 24 people, injured many more, and caused billions of dollars in damage. After that tornado, the City of Moore passed building codes requiring new homes be built to withstand at least EF2 wind speeds.

Learn ways to prepare for tornadoes.

Earthquake Magnitude Scales

The Richter Magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology and was followed later by many additional magnitude scales. The Moment Magnitude scale is used to rate the magnitude (the amount of energy released) of an earthquake, and is preferred by scientists to determine earthquake magnitudes today. Magnitude is not determined by assessing the damage caused by an earthquake but by using the shaking recorded at the surface as measured by instruments known as seismographs.(6)Graphic depicting earthquake waveforms

Magnitude is expressed on the Moment Magnitude scale in whole numbers and decimal fractions. A whole number increase in magnitude represents a tenfold increase in measured energy. Each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

Another important scale used by earthquake scientists is the Modified Mercalli Intensity (MMI) scale. The MMI scale estimates the intensity of shaking in the region around the earthquake epicenter with a range of values that varies across the landscape corresponding to felt reports of shaking and damage.

An earthquake with a magnitude of 6.7 struck the southern California city of Northridge in 1994. The quake killed 57 people, injured more than 9,000, and displaced over 20,000. It caused an estimated $20 billion in property losses and infrastructure damages. It is considered the costliest earthquake in U.S. history.(7)

As a result, building codes changed and retrofitting was done at hospitals and on freeways and water pipes to mitigate (or reduce) the effect of the next earthquake.(8, 9) State and local responders are prepared for the next earthquake with emergency plans and early warning systems, like the MyShake App.

Learn ways to prepare for earthquakes.

Reference

  1. https://www.noaa.gov/media-release/record-breaking-atlantic-hurricane-season-draws-to-end
  2. https://www.nhc.noaa.gov/aboutsshws.php
  3. https://www.nhc.noaa.gov/surge/
  4. https://www.weather.gov/oun/efscale
  5. https://www.spc.noaa.gov/faq/tornado/f5torns.html
  6. https://www.usgs.gov/faqs/moment-magnitude-richter-scale-what-are-different-magnitude-scales-and-why-are-there-so-many?qt-news_science_products=0#qt-news_science_products
  7. https://www.usgs.gov/faqs/seismometers-seismographs-seismograms-whats-difference-how-do-they-work?qt-news_science_products=0#qt-news_science_products
  8. https://www.usgs.gov/media/videos/northridge-ca-earthquake-open-file-report-94-179-i
  9. https://www.npr.org/2019/01/17/686020821/25-years-after-the-northridge-earthquake-is-la-ready-for-the-big-one

Resources

Thanks in advance for your questions and comments on this Public Health Matters post. Please note that the CDC does not give personal medical advice. If you are concerned you have a disease or condition, talk to your doctor.

Have a question for CDC? CDC-INFO (http://www.cdc.gov/cdc-info/index.html) offers live agents by phone and email to help you find the latest, reliable, and science-based health information on more than 750 health topics.

Stay Informed: How Scales Help Us Describe Disasters

Photo of palm trees bending in gale force winds

Last year’s Atlantic hurricane season was record-breaking. There were 30 named storms during the 2020 season. Thirteen of those became hurricanes (top winds of 74 mph or greater). Six of those reached Category 3 or higher.(1)

Hurricanes are categorized using the Saffir-Simpson Hurricane Wind Scale. Other scales are used by experts to explain and describe the intensity or severity of disasters like tornadoes and earthquakes. Below are descriptions of some of them.

The Saffir-Simpson Hurricane Wind Scale

The Saffir-Simpson Hurricane Wind Scale was created in 1971 by civil engineer Herbert Saffir and meteorologist Robert Simpson. Hurricanes are rated (or categorized) 1 to 5 based on their maximum sustained wind speed. The category relates wind speed to the kinds of property damage that are likely to occur from wind.(2)

All hurricanes produce life-threatening winds, but only storms rated Category 3 and higher are considered major hurricanes. Major hurricanes cause devastating to catastrophic wind damage.Hurricane evacuation sign

Hurricanes of all categories can produce storm surge that requires people to evacuate and take other preventative measures.

The Saffir-Simpson scale only provides information about wind damage. It does not describe damage from other hazards, such as storm surge, inland flooding, or tornadoes spawned by the storm.

Along the coast, storm surge is often the greatest threat to life and property from a hurricane. At least 1,500 people died during Hurricane Katrina in 2005. Many of those deaths are attributed either directly or indirectly to storm surge.(3)

Evacuation orders are more likely to be based on storm surge or inland flooding than on the Saffir-Simpson category. It is critical for emergency officials and the public to stay informed of the forecast and to prepare regardless of whether they live near the coast or well inland.

Learn ways to prepare for hurricanes.

The Enhanced Fujita Scale

Researcher Ted Fujita and Allen Pearson of the National Weather Service (NWS), introduced the original Fujita Scale for rating tornadoes in 1971.

Wind researchers and engineers provided substantial enhancements to the scale in the early 2000s, called the Enhanced Fujita (EF) Scale. NWS adopted the scale in 2007. Like the F-Scale, the EF Scale estimates a tornado’s intensity on a scale, from 0 to 5, based on surveyed damage.(4)

Photo of person in the foreground of residential tornado destruction
Photo credit: FEMA

NWS is the only federal agency with the authority to provide official ratings for tornadoes. Ratings are not based on actual measurements of wind speed; although, some researchers have equipment that can estimate speeds through radar velocity data. Ratings are estimates of wind speed based on assessed damage to structures and vegetation. The result is a range of likely
wind speeds.

The most recent EF5 tornado struck Moore, Okla., in May 2013.(5) It killed 24 people, injured many more, and caused billions of dollars in damage. After that tornado, the City of Moore passed building codes requiring new homes be built to withstand at least EF2 wind speeds.

Learn ways to prepare for tornadoes.

Earthquake Magnitude Scales

The Richter Magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology and was followed later by many additional magnitude scales. The Moment Magnitude scale is used to rate the magnitude (the amount of energy released) of an earthquake, and is preferred by scientists to determine earthquake magnitudes today. Magnitude is not determined by assessing the damage caused by an earthquake but by using the shaking recorded at the surface as measured by instruments known as seismographs.(6)Graphic depicting earthquake waveforms

Magnitude is expressed on the Moment Magnitude scale in whole numbers and decimal fractions. A whole number increase in magnitude represents a tenfold increase in measured energy. Each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

Another important scale used by earthquake scientists is the Modified Mercalli Intensity (MMI) scale. The MMI scale estimates the intensity of shaking in the region around the earthquake epicenter with a range of values that varies across the landscape corresponding to felt reports of shaking and damage.

An earthquake with a magnitude of 6.7 struck the southern California city of Northridge in 1994. The quake killed 57 people, injured more than 9,000, and displaced over 20,000. It caused an estimated $20 billion in property losses and infrastructure damages. It is considered the costliest earthquake in U.S. history.(7)

As a result, building codes changed and retrofitting was done at hospitals and on freeways and water pipes to mitigate (or reduce) the effect of the next earthquake.(8, 9) State and local responders are prepared for the next earthquake with emergency plans and early warning systems, like the MyShake App.

Learn ways to prepare for earthquakes.

Reference

  1. https://www.noaa.gov/media-release/record-breaking-atlantic-hurricane-season-draws-to-end
  2. https://www.nhc.noaa.gov/aboutsshws.php
  3. https://www.nhc.noaa.gov/surge/
  4. https://www.weather.gov/oun/efscale
  5. https://www.spc.noaa.gov/faq/tornado/f5torns.html
  6. https://www.usgs.gov/faqs/moment-magnitude-richter-scale-what-are-different-magnitude-scales-and-why-are-there-so-many?qt-news_science_products=0#qt-news_science_products
  7. https://www.usgs.gov/faqs/seismometers-seismographs-seismograms-whats-difference-how-do-they-work?qt-news_science_products=0#qt-news_science_products
  8. https://www.usgs.gov/media/videos/northridge-ca-earthquake-open-file-report-94-179-i
  9. https://www.npr.org/2019/01/17/686020821/25-years-after-the-northridge-earthquake-is-la-ready-for-the-big-one

Resources

Thanks in advance for your questions and comments on this Public Health Matters post. Please note that the CDC does not give personal medical advice. If you are concerned you have a disease or condition, talk to your doctor.

Have a question for CDC? CDC-INFO (http://www.cdc.gov/cdc-info/index.html) offers live agents by phone and email to help you find the latest, reliable, and science-based health information on more than 750 health topics.

Did you know ‘storm spotters’ in your community keep you safe during severe weather?

Civic minded citizen scientists in your community help meteorologists and the National Weather Service stay abreast of inclement weather with on-the-ground data. Earlier this week, the Midwest and Northeast were slammed with tornados and thunderstorms that grounded planes and held … Continue reading »

The post Did you know ‘storm spotters’ in your community keep you safe during severe weather? appeared first on PLOS Blogs Network.

An Unpredictable Spring

Be Prepared Header

“In the spring I have counted one hundred and thirty-six kinds of weather inside of four and twenty hours.” – Mark Twain

While spring officially sprung in late March, it’s only been in the last few weeks that we’ve seen the characteristically unpredictable weather that ushers in the fun-in-the-sun summer. During spring, temperatures can swing back and forth between balmy (high 80s in Georgia this week) and frigid (in the 40s in Wyoming). Sunny days may be followed by a week of stormy weather; sometimes extreme weather changes can occur even within the same day.

Below are the most common types of severe spring weather:

  • Be Ready for Tornadoes InfographicThunderstorms cause most of the severe spring weather. They can bring lightning, tornadoes and flooding. Whenever warm, moist air collides with cool, dry air, thunderstorms can occur. For much of the world, this happens in spring and summer.
  • Tornadoes, often called twisters, are rapidly rotating columns of air that are connected to both the ground and the cloud.  Tornado Alley – the Great Plains region of the United States – is most active this time of year.  Already in 2014, there have been more than 30 deaths due to tornadoes.
  • Flooding, which is most common in and near mountainous areas due to snow melt, is another condition of spring.  As are mudslides, like the one in Oso, Washington, in late March.  Mudslides happen when heavy rainfall, snowmelt, or high amounts of ground water cause soil to be uprooted.   
  • Wildfires are most common in the Western United States and wildfire season usually starts in May and runs through August.  According to the National Interagency Fire Center, this year’s wildfire season could be dangerous.

Because spring weather can be so unpredictable, you may be unprepared when severe weather hits—especially if you live in a region that does not often experience these types of events. And when severe weather hits unexpectedly, the risk of injury and death increases. So planning ahead makes sense; prepare for storms, floods, and tornadoes as if you know in advance they are coming, because in the spring, they very likely will.

Advance planning for thunderstorms, lightning, tornadoes and floods requires specific safety precautions. Still, you can follow many of the same steps for all extreme weather events. You should have on hand:

  • A battery-operated flashlight, a battery-operated NOAA Weather Radio, and extra batteries for both
  • An emergency evacuation plan, including a map of your home and, for every type of severe weather emergency, routes to safety from each room
  • A list of important personal information, including
    • telephone numbers of neighbors, family and friends
    • insurance and property information
    • telephone numbers of utility companies
    • medical information
  • A first aid kit may include:
    • non-latex gloves
    • assortment of adhesive bandages
    • antibiotic ointment
    • sterile gauze pads in assorted sizes
    • absorbent compress dressings
    • tweezers
    • scissors
    • adhesive cloth tape
    • aspirin packets (81 mg each)
    • First aid instruction booklet
  • A 3–5 day supply of bottled water and nonperishable food
  • Personal hygiene items
  • Blankets or sleeping bags
  • An emergency kit in your car

Remember to help prepare your family members and neighbors for the possibility of severe weather too. Tell them where they can find appropriate shelter as soon as they are aware of an approaching storm. Make sure to run through your emergency plans for every type of severe weather. Show family members where emergency supplies are stored, and make sure they know how to turn off the water, gas, and electricity in your home.

Unfortunately, few of us get much advance notice of a severe weather event. Often times when we become aware of an approaching storm, we have little time to prepare for it.  But, we know what season it is, and even if this spring doesn’t bring any severe weather to your area, being prepared can help you at any time of the year.

Are there any stories of your own spring preparedness that you want to share with us?