What Threats exist from severe weather?
Severe weather comes in many different forms that all have an impact on every day life. Most forms have the ability to be fatal and in order to avoid injury, or perhaps even death, you must know what the threat is and what the potential impacts it has in order to protect yourself.
Tornadoes
High Winds
Lightning
Flash Flooding
Hail
Tornadoes are defined as rapidly rotating columns of air that are in contact with the surface. They form
from intense thunderstorms, known as supercells. Supercells have pre-existing rotation within them which
is the main reason why tornadoes are more likely within these storms. Tornadoes have formed from non-supercell
storms, but tend to be rare.
Tornado winds are estimated by the National Weather Service by the
enhanced Fujita scale that assesses the damage from the tornado to imply the winds. The scale goes from
EF-0 (winds between 65-85 mph) up to EF-5 (winds over 200 mph). EF-5 tornadoes will completely level a house as seen
from the famous Greensburg, KS and Parkersburg, IA EF-5 tornadoes.
As a tornado approaches winds will slowly pick up and
move in towards the tornado. The tornado will pass relatively quickly as it moves with about the same speed as the parent thunderstorm. The winds
will then reverse, again towards the tornado.
The largest threat from tornadoes are the debris they carry. With such strong winds large
items of debris will fly through the air at tremendous speeds. Horrific stories of people getting planks embedded in their bodies during large
tornadoes have been documented. Most people die by the debris, not by the tornado itself.
Threat Level: 6/10
High winds, also known as straight line winds, come from intense thunderstorms called squall lines. A squall line is a line of
numerous thunderstorms making one large, linear system that tend to be oriented from north to south. The linear setup allows for
the dynamics to come together to produce dangerous straight line wind damgage that is comparable to that of weaker tornadoes.
The main threat from high winds, once again, is debris. High winds may snap tree branches or even tear roofs of houses. Even though the
overall magnitude of high winds tend to be weaker than tornadoes, they still possess enough energy to put life at risk. Extreme events of
squall lines may go for hundreds of miles, leaving a comparable damage path. These events are known as Derecho events.
Threat Level: 3/10
Lightning is formed when differential charge builds up between the clouds and near the ground. Lightning is the dischard of this built of charge. This built of charge is formed by thunderstorm updrafts interacting with cloud molecules building a charge that tends to be negative near the base of the storm and positive near the ground. Sometimes the charge is switched creating the rare "postive" stroke which tends to be more energentic creating very loud thunder. All thunderstorms contain lightning, as this is what they are defined by. Strikes may occur within the cloud, called cloud-to-cloud lightning or they may reach the ground which is known as cloud-to-ground lightning. Lightning may occur as the thunderstorm is developing or dying and has very little bearing on how the strong the storm is itself. The danger is always present when an updraft feeding a cloud is present. Lightning can strike 10 miles away from any given storm.
Threat Level: 5/10
Flash flooding takes the most lives, on average, of Americans making them of particular interest. Flash floods occur when torrential rainfall occurs in one location over a short time. This usually happens when either a particular storm is moving slowly or numerous storms continue to move over the same location for an extended period of time. Flood waters may rise in terms of feet in a matter of an hour if enough rain falls. This makes warning these events fairly difficult and many times catch people by suprise. Most people who do die from flash flooding, die from being inside a vehicle. It only takes approximately six inches of water to overtake a vehicle and a standing human.x
Threat Level: 8/10
Hail is formed when intense thunderstorm updrafts grab raindrops, send them past the freezing level, freeze the water, then fall down, coat the ice pellet with water, then get dragged back up by the updraft, and the process repeats until the stone becomes to heavy for the updraft to hold it up. Hail typically is spherically in shape and may reach to about 4" is diameter. Most hail reports come in around 3/4" and the National Weather Service will issue a severe thunderstorm warning if hail of 1" or greater is expected. Typically the stronger the storm, the larger the hail. Hail takes very little life and is not so much a risk to life as it is to property. Hailstones need to be of fairly large size in order to be considered "lethal". Hail gives farmers, car owners, and home owners headaches as crops and windows tend to be broken in hail storms.