The National Weather Service recently released two reports on the Mississippi-Alabama-Georgia tornado outbreak of 2011, and the Joplin, Missouri tornado of May 22, 2011.
The Mississippi-Alabama-Georgia report can be found at http://www.nws.noaa.gov/os/assessments/pdfs/historic_tornadoes.pdf
The Joplin report can be found at http://www.nws.noaa.gov/os/assessments/pdfs/Joplin_tornado.pdf
The first report on the April 25-28, 2011 events, ranked as the third-worst tornado outbreak since 1950, provides a comprehensive review of the activities of various National Weather Service forecast offices across the states of Mississippi, Alabama, and Georgia. Interestingly, the weather service sought the support and input of social scientists when reviewing these events. Specifically, the weather service is acutely interested in how severe weather and tornado warnings are received by the community and how the warnings are acted upon.
The growth of smart-phone technology places a tremendous warning dissemination resource in the pockets of many. Even non-smart-phones that receive only calls and simple text messages can be a powerful tool. In the report on the April outbreak, the weather service found that "Peer warnings helped motivate people to take protective action. Nearby family and friends supplemented the warning system through personal contact," referring to friends and family using mobile communications technology to warn their neighbors and relatives of the oncoming storms. What does that mean? It means that you are a vital part of the warning chain. Don't hesitate pass information along, or assume that others are aware of warnings. A number of other "best practices" are offered in the report as well, some exclusive to the weather service, but many are applicable to the public.
A recurrent topic that is not limited to these two reports is that we should seek more than one source for weather warning information. NOAA Weather Radio provides a direct link from the weather service, but it is not infallible, as at least one NOAA transmitter was struck by an Alabama tornado. Utilizing multiple sources provides you the greatest potential to receive warnings in a timely manner.
Another salient point raised was the perception that people felt they needed personal, visual confirmation that a storm was going to affect them. The NWS strives to increase warning accuracy by carefully defining the warned area along the expected path of a storm. In waiting for visual confirmation of the imminent arrival of a tornado, persons in the path reduced their window of opportunity to seek shelter. In these cases, adequate warning lead-time had been given, yet people put themselves in unnecessary danger by "waiting to see."
Possibly the most important point to take from these reports is one that is not written in them. That point is that you are ultimately responsible for your actions before, during, and after a severe weather event. The National Weather Service, your county emergency management, your city public safety officials, and broadcast media can not provide you with instant, specific, and personalized instruction on how you should respond to an imminent weather emergency. Knowing how to receive warnings, how to interpret and react to them, and when, where, and how to take shelter are your life-saving responsibilities.
I encourage you to take some time to read through these reports, especially the sections that look at warning times, and public reception and actions based on the warnings.
Showing posts with label Severe Weather Awareness Week. Show all posts
Showing posts with label Severe Weather Awareness Week. Show all posts
Tuesday, December 20, 2011
Wednesday, February 23, 2011
Severe Weather Awareness Week - Lightning
EVERY THUNDERSTORM CONTAINS LIGHTNING.
Nationwide in 2010, 30 people were killed by lightning. Since 1959 a staggering 3919 people have lost their lives as a direct result of being struck. In an average year around 25 million lightning strikes are recorded across the United State alone. Worldwide there are around 1800 thunderstorms ongoing at any given time. Lightning is an incredibly powerful electrical discharge, containing up to 100 million volts of electrical charge and capable of reaching 50000 degrees Fahrenheit. Cloud to Ground Lightning is the result of incredible differences in electrical charge which forms within thunderstorms…as well as between thunderstorms and the earth’s surface. Recent science suggests that ice in thunderstorms is key to creating the massive charge differences which lead to lightning. Thunderstorm updrafts and downdrafts work to separate smaller
ice particles from larger hail stones within the storm. As this happens many of the ice pieces collide resulting in a separation of electrical charge. The higher part of the storm contains primarily positively charged small ice crystals, with negative charged larger chunks of ice down low. As the storm moves across the earth a pool of positively charged particles gathers near the ground. Eventually a brief electrical circuit is created as a negatively charged “step leader” descends from the storm toward the ground and eventually connects to the positive charge on the ground. The extreme heating of the air with lightning causes a rapid expansion of the air around it, leading to thunder. The sound of thunder will travel away from lightning at a speed around 1 mile every 5 seconds. If you can see lightning and hear thunder at your location you are not safe, if you hear thunder within 30 seconds after seeing lightning your life is in immediate danger.
Lightning Safety Rules—Outdoors
Seek shelter inside a house, large building or an all metal vehicle with the windows rolled up (avoid convertibles).
If your hair stands on end and your skin tingles... lightning is about to strike. Take cover immediately!
When boating, head for shore and get into a shelter, or vehicle. If caught in a boat, lie down in the boat with cushions between you and the boat's side and bottom.
Large trees, hilltops and other high places.
Chain link fences and any other metal fences like those around ball parks and play grounds.
Motorcycles, scooters, golf carts, small metal sheds, bicycles, tractors and farm equipment that does not have an enclosed metal cab.
Lightning Safety Rules - Indoors
Stay away from windows. Avoid telephones and electrical appliances (wires connecting to these devices run
outside of the home and act as lightning rods). Don’t wash dishes or take a shower. The pipes will conduct
electricity.
Unplug computers and other sensitive electrical devices (time permitting) since surge suppressors may not protectthese items if lightning hits close to the home.
Remember, there is no truth to the old myth that ―lightning never strikes twice.
Take time this week to learn or refresh your memory on lightning safety rules. That quick dash out in the open when athunderstorm is in progress may unnecessarily expose you to the possibility of being struck. It is not worth the risk.
If a person is struck by lightning, there is no residual charge left on the body. The quick application of CPR
may maintain vital body functions until medical help can be obtained.
Nationwide in 2010, 30 people were killed by lightning. Since 1959 a staggering 3919 people have lost their lives as a direct result of being struck. In an average year around 25 million lightning strikes are recorded across the United State alone. Worldwide there are around 1800 thunderstorms ongoing at any given time. Lightning is an incredibly powerful electrical discharge, containing up to 100 million volts of electrical charge and capable of reaching 50000 degrees Fahrenheit. Cloud to Ground Lightning is the result of incredible differences in electrical charge which forms within thunderstorms…as well as between thunderstorms and the earth’s surface. Recent science suggests that ice in thunderstorms is key to creating the massive charge differences which lead to lightning. Thunderstorm updrafts and downdrafts work to separate smaller
ice particles from larger hail stones within the storm. As this happens many of the ice pieces collide resulting in a separation of electrical charge. The higher part of the storm contains primarily positively charged small ice crystals, with negative charged larger chunks of ice down low. As the storm moves across the earth a pool of positively charged particles gathers near the ground. Eventually a brief electrical circuit is created as a negatively charged “step leader” descends from the storm toward the ground and eventually connects to the positive charge on the ground. The extreme heating of the air with lightning causes a rapid expansion of the air around it, leading to thunder. The sound of thunder will travel away from lightning at a speed around 1 mile every 5 seconds. If you can see lightning and hear thunder at your location you are not safe, if you hear thunder within 30 seconds after seeing lightning your life is in immediate danger.
Lightning Safety Rules—Outdoors
Seek shelter inside a house, large building or an all metal vehicle with the windows rolled up (avoid convertibles).
If your hair stands on end and your skin tingles... lightning is about to strike. Take cover immediately!
When boating, head for shore and get into a shelter, or vehicle. If caught in a boat, lie down in the boat with cushions between you and the boat's side and bottom.
AVOID
Large trees, hilltops and other high places.
Chain link fences and any other metal fences like those around ball parks and play grounds.
Motorcycles, scooters, golf carts, small metal sheds, bicycles, tractors and farm equipment that does not have an enclosed metal cab.
Lightning Safety Rules - Indoors
Stay away from windows. Avoid telephones and electrical appliances (wires connecting to these devices run
outside of the home and act as lightning rods). Don’t wash dishes or take a shower. The pipes will conduct
electricity.
Unplug computers and other sensitive electrical devices (time permitting) since surge suppressors may not protectthese items if lightning hits close to the home.
Remember, there is no truth to the old myth that ―lightning never strikes twice.
Take time this week to learn or refresh your memory on lightning safety rules. That quick dash out in the open when athunderstorm is in progress may unnecessarily expose you to the possibility of being struck. It is not worth the risk.
If a person is struck by lightning, there is no residual charge left on the body. The quick application of CPR
may maintain vital body functions until medical help can be obtained.
Tuesday, February 22, 2011
Severe Weather Awareness Week - Tornadoes
What is a Tornado?
A tornado is a violently rotating column of air that extends from the base of a storm cloud to the ground.
Some conditions that are conducive for tornado formation include warm, moist, unstable air, strong atmospheric winds that increase in speed and change direction with height, and a forcing mechanism to lift the
air. When a combination of these factors comes together just right, tornadoes form. The most common time of year for tornado formation in Mississippi is during the spring months of March, April, and May, with a
Tornado - Robertson Co.- January 2010 secondary tornado season in November. Additionally, the afternoon and evening hours are the times of day at which most tornadoes occur, as they are the times at which the maximum heating takes place. However, tornadoes can occur at any time of day, and at any point during the year, given the right environment. Many tornadoes occur at night in Mississippi.
Nighttime Tornadoes Pose Greater Danger
The NWS would like to draw attention to nighttime tornadoes. These tornadoes pose a greater danger than those that occur during the daylight because once most people go to bed, they are no longer connected to the watches or warnings issued by the NWS. Also at night, visibility is reduced and observing a tornado is more difficult. This is elevated during the winter months because it is not the traditional tornado season. Research by Gagan et al. 2010 compared tornado statistics from the Great Plains in the classic “Tornado Alley” to tornadoes in the Deep South or “Dixie Alley.” Researchers found that Dixie Alley had far greater amounts of Killer Strong/Violent Tornadoes between 9pm-9am timeframe. Dixie Alley had nearly twice the number of strong/violent tornadoes from Midnight-Noon timeframe than Tornado Alley from 1950-2007.
Having an properly programmed All Hazards NOAA Weather Radio with S.A.M.E. County Coding technology will alarm individuals anytime of day when a severe thunderstorm warning or tornado warning is issued for their county. This device has been credited for saving numerous lives during nocturnal tornado events.
**Source: National Weather Service - Jackson, MS Forecast Office, Mississippi Severe Weather Awareness Week 2011 Brochure which can be viewed/downloaded by clicking the link.
A tornado is a violently rotating column of air that extends from the base of a storm cloud to the ground.
Some conditions that are conducive for tornado formation include warm, moist, unstable air, strong atmospheric winds that increase in speed and change direction with height, and a forcing mechanism to lift the
air. When a combination of these factors comes together just right, tornadoes form. The most common time of year for tornado formation in Mississippi is during the spring months of March, April, and May, with a
Tornado - Robertson Co.- January 2010 secondary tornado season in November. Additionally, the afternoon and evening hours are the times of day at which most tornadoes occur, as they are the times at which the maximum heating takes place. However, tornadoes can occur at any time of day, and at any point during the year, given the right environment. Many tornadoes occur at night in Mississippi.
Nighttime Tornadoes Pose Greater Danger
The NWS would like to draw attention to nighttime tornadoes. These tornadoes pose a greater danger than those that occur during the daylight because once most people go to bed, they are no longer connected to the watches or warnings issued by the NWS. Also at night, visibility is reduced and observing a tornado is more difficult. This is elevated during the winter months because it is not the traditional tornado season. Research by Gagan et al. 2010 compared tornado statistics from the Great Plains in the classic “Tornado Alley” to tornadoes in the Deep South or “Dixie Alley.” Researchers found that Dixie Alley had far greater amounts of Killer Strong/Violent Tornadoes between 9pm-9am timeframe. Dixie Alley had nearly twice the number of strong/violent tornadoes from Midnight-Noon timeframe than Tornado Alley from 1950-2007.
Having an properly programmed All Hazards NOAA Weather Radio with S.A.M.E. County Coding technology will alarm individuals anytime of day when a severe thunderstorm warning or tornado warning is issued for their county. This device has been credited for saving numerous lives during nocturnal tornado events.
**Source: National Weather Service - Jackson, MS Forecast Office, Mississippi Severe Weather Awareness Week 2011 Brochure which can be viewed/downloaded by clicking the link.
Severe Weather Awareness Week - Flash Floods
FLASH FLOODING: Flash floods can occur within a few minutes or up to 6 hours after excessive rainfall, a dam or levee failure, or a sudden release of water held by an ice jam or mud slide. Flash floods can wash out roads, destroy buildings an d bridges. Because flash floods happen in a short period of time (less than six hours after the causative event) they are more life threatening than other types of flooding. Areas most susceptible to flash flooding are mountainous streams and rivers, urban areas, low-lying areas, storm drains, and culverts.
A Flash Flood Warning is issued when flash flooding has been reported or is imminent. It focuses on specific communities, creeks or streams, or other geographic areas where flooding is imminent or occurring.
RIVER FLOODING: This type of flooding is caused by an increased water level in established watercourses, such as a rivers, creeks, or streams. River flooding is slower to develop than flash flooding (more than 6 hours after the causative event), however, some smaller creeks and streams have a short lag time between the runoff from heavy rain and the onset of flooding. On the other hand, it may take several days for a flood crest to pass downstream points on major rivers such as the Lower Pearl, and Mississippi Rivers. The NWS issues River Flood Warnings when rivers are expected to rise above flood stage. Persons in the warned area are advised to take necessary precautions immediately. River stages and crest forecasts are given for selected forecast points along with known flood stages for each forecast point. While there is usually more advanced warning time with river floods than with flash floods, persons should be familiar with the flood prone areas they live and work in, and must know what action to take and where to go if a flood occurs. Advance planning and preparation is essential.
FLOOD SAFETY RULES: Follow these tips to stay safe during flood conditions…
When a warning is issued get out of areas subject to flooding. These may include dips, low spots, stream beds, drainage ditches and culverts. If caught in low areas during flooding, go to high ground immediately.
Avoid already flooded and high velocity flow areas. A rapidly flowing stream or ditch can sweep you off your feet or even carry your car or truck downstream. Never drive through a flooded area as the road bed may be washed away. Play it safe! If you encounter a flooded road - TURN AROUND, DON’T DROWN!
Be especially cautious at night when it is harder to recognize flood conditions, and never drive around a barricaded road.
Most flood deaths occur at night and when people become trapped in automobiles that stall in areas that are flooded. If your vehicle stalls, abandon it immediately and seek higher ground. The rising water may engulf the vehicle and the occupants inside. Do not camp or park your vehicle along streams or washes during threatening conditions.
When a FLOOD WARNING is issued for your area, act quickly to save yourself. You may only have seconds!
**Source: National Weather Service - Jackson, MS Forecast Office, Mississippi Severe Weather Awareness Week 2011 Brochure which can be viewed/downloaded by clicking the link.
A Flash Flood Warning is issued when flash flooding has been reported or is imminent. It focuses on specific communities, creeks or streams, or other geographic areas where flooding is imminent or occurring.
RIVER FLOODING: This type of flooding is caused by an increased water level in established watercourses, such as a rivers, creeks, or streams. River flooding is slower to develop than flash flooding (more than 6 hours after the causative event), however, some smaller creeks and streams have a short lag time between the runoff from heavy rain and the onset of flooding. On the other hand, it may take several days for a flood crest to pass downstream points on major rivers such as the Lower Pearl, and Mississippi Rivers. The NWS issues River Flood Warnings when rivers are expected to rise above flood stage. Persons in the warned area are advised to take necessary precautions immediately. River stages and crest forecasts are given for selected forecast points along with known flood stages for each forecast point. While there is usually more advanced warning time with river floods than with flash floods, persons should be familiar with the flood prone areas they live and work in, and must know what action to take and where to go if a flood occurs. Advance planning and preparation is essential.
FLOOD SAFETY RULES: Follow these tips to stay safe during flood conditions…
When a warning is issued get out of areas subject to flooding. These may include dips, low spots, stream beds, drainage ditches and culverts. If caught in low areas during flooding, go to high ground immediately.
Avoid already flooded and high velocity flow areas. A rapidly flowing stream or ditch can sweep you off your feet or even carry your car or truck downstream. Never drive through a flooded area as the road bed may be washed away. Play it safe! If you encounter a flooded road - TURN AROUND, DON’T DROWN!
Be especially cautious at night when it is harder to recognize flood conditions, and never drive around a barricaded road.
Most flood deaths occur at night and when people become trapped in automobiles that stall in areas that are flooded. If your vehicle stalls, abandon it immediately and seek higher ground. The rising water may engulf the vehicle and the occupants inside. Do not camp or park your vehicle along streams or washes during threatening conditions.
When a FLOOD WARNING is issued for your area, act quickly to save yourself. You may only have seconds!
**Source: National Weather Service - Jackson, MS Forecast Office, Mississippi Severe Weather Awareness Week 2011 Brochure which can be viewed/downloaded by clicking the link.
Monday, February 21, 2011
Severe Weather Awareness Week - Severe Thunderstorms
Each day this week, we'll post information on various aspects of severe weather for Severe Weather Awareness Week 2011. Feel free copy, paste, or share this information. Today, we discuss severe thunderstorms and hail.
What is a Severe Thunderstorm?
A severe thunderstorm is a thunderstorm that produces one or more of the following: hail that has a diameter of one inch (quarter size) or larger, winds greater than or equal to 58 mph, and tornadoes. About 10% of all thunderstorms in the U.S. meet severe criteria.
Severe thunderstorms can occur at any time of year, although the most common time of occurrence is during the spring months of March, April, and May. In addition, pulse-type thunderstorms during the summer months can produce high winds, frequent lightning, and torrential downpours.
There is also a secondary season of organized severe weather in Mississippi, in November and early December.
What is the Difference between a Watch and a Warning?
A severe thunderstorm watch means that conditions are favorable for severe thunderstorms to develop. These are issued by the Storm Prediction Center in Norman, OK, typically before severe weather is developing.
A severe thunderstorm warning means that a severe thunderstorm has either been indicated on radar or witnessed by storm spotters. Your local NWS Forecast Office issues severe thunderstorm warnings when severe weather is developing or occurring.
How Is Hail Formed?
Hail is formed when water droplets are drawn into an area of strong upward moving air, known as an up-
draft, of a storm. Once the water droplets are transported above the freezing level, they combine with tiny airborne particles, such as dirt, salt, volcanic ash, etc., and freeze on contact, forming tiny ice particles. These ice particles are light enough that they remain suspended in the cloud, where they undergo processes that allow them to combine with other supercooled water droplets and grow into hail stones. Once the hail stones are heavy enough to overcome the upward force of the updraft, they fall out of the cloud. By definition, hail stones are 5 millimeters or larger, and can inflict significant damage to automobiles, buildings, crops, and even people.
Mississippi's primary season for significant hail (1 inch or larger) runs from March to May, but hail is possible year-round.
As of January 5, 2010, the National Weather Service has changed the severe hail criteria from 3/4 inch to 1 inch. Why the change? There are a couple of reasons. Research has shown that significant damage caused by hail does not occur until the hail diameter reaches one inch (approximately quarter size) or larger. Requests from NWS partners such as emergency managers and the media further prompted the decision to increase the severe hail criteria due to the fact that more frequent severe thunderstorm warnings may act to desensitize the public from their meaningfulness. Such an effect could cause people not to take caution during such a warning, which could lead to unnecessary damage or injury. The change means that severe thunderstorm warnings for hail will be issued less frequently so that a greater emphasis can be placed on more substantial hail threats.
Hail Size Estimates
Pea - 1/4 inch
Penny - 3/4 inch
Quarter - 1 inch
Half Dollar - 1 1/4 inches
Golf Ball - 1 3/4 inches
Tennis Ball - 2 1/2 inches
Baseball - 2 3/4 inches
Grapefruit - 4 inches
**Source: National Weather Service - Jackson, MS Forecast Office, Mississippi Severe Weather Awareness Week 2011 Brochure which can be viewed/downloaded by clicking the link.
What is a Severe Thunderstorm?
A severe thunderstorm is a thunderstorm that produces one or more of the following: hail that has a diameter of one inch (quarter size) or larger, winds greater than or equal to 58 mph, and tornadoes. About 10% of all thunderstorms in the U.S. meet severe criteria.
Severe thunderstorms can occur at any time of year, although the most common time of occurrence is during the spring months of March, April, and May. In addition, pulse-type thunderstorms during the summer months can produce high winds, frequent lightning, and torrential downpours.
There is also a secondary season of organized severe weather in Mississippi, in November and early December.
What is the Difference between a Watch and a Warning?
A severe thunderstorm watch means that conditions are favorable for severe thunderstorms to develop. These are issued by the Storm Prediction Center in Norman, OK, typically before severe weather is developing.
A severe thunderstorm warning means that a severe thunderstorm has either been indicated on radar or witnessed by storm spotters. Your local NWS Forecast Office issues severe thunderstorm warnings when severe weather is developing or occurring.
How Is Hail Formed?
Hail is formed when water droplets are drawn into an area of strong upward moving air, known as an up-
draft, of a storm. Once the water droplets are transported above the freezing level, they combine with tiny airborne particles, such as dirt, salt, volcanic ash, etc., and freeze on contact, forming tiny ice particles. These ice particles are light enough that they remain suspended in the cloud, where they undergo processes that allow them to combine with other supercooled water droplets and grow into hail stones. Once the hail stones are heavy enough to overcome the upward force of the updraft, they fall out of the cloud. By definition, hail stones are 5 millimeters or larger, and can inflict significant damage to automobiles, buildings, crops, and even people.
Mississippi's primary season for significant hail (1 inch or larger) runs from March to May, but hail is possible year-round.
As of January 5, 2010, the National Weather Service has changed the severe hail criteria from 3/4 inch to 1 inch. Why the change? There are a couple of reasons. Research has shown that significant damage caused by hail does not occur until the hail diameter reaches one inch (approximately quarter size) or larger. Requests from NWS partners such as emergency managers and the media further prompted the decision to increase the severe hail criteria due to the fact that more frequent severe thunderstorm warnings may act to desensitize the public from their meaningfulness. Such an effect could cause people not to take caution during such a warning, which could lead to unnecessary damage or injury. The change means that severe thunderstorm warnings for hail will be issued less frequently so that a greater emphasis can be placed on more substantial hail threats.
Hail Size Estimates
Pea - 1/4 inch
Penny - 3/4 inch
Quarter - 1 inch
Half Dollar - 1 1/4 inches
Golf Ball - 1 3/4 inches
Tennis Ball - 2 1/2 inches
Baseball - 2 3/4 inches
Grapefruit - 4 inches
**Source: National Weather Service - Jackson, MS Forecast Office, Mississippi Severe Weather Awareness Week 2011 Brochure which can be viewed/downloaded by clicking the link.
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