Severe Local Storms

What percent of yearly deaths are caused by severe weather?

75%

The US has sustained _______ climate disasters since 1980 where overall damages/ costs reached $1 billion

about 300

What is the difference between weather and climate?

weather is short term process changes daily and climate is a long-term process

“Climate is what you _____, weather is what you _______”

expect, get

Ingredients for a thunderstorm

moisture, instability, a lifting mechanism, sometimes shear

Shear

a difference in wind speed an direction over some distance in the atmosphere (rotation)

Phenomenology

storms exist on a continuous spectrum; a storm may pass through a multitude of classifications

Types of thunderstorm cells

Ordinary: short lived, less organized

Multi-cells (line or cluster): regenerate new cells, cause squall lines and more severe storms

Supercells: sustained and rotating updraft, longer lived

Supercells

most intense T-storm type, updrafts and downdrafts allow it to maintain itself for many hours, can produce grapefruit sized hail

Forward flank downdraft (FFD)

outflow from the rain-cooled air of the storm’s main downdraft

Rear flank downdraft (RFD)

dry downdraft, very important for tornado-genesis

_____ % of annual thunderstorm insured losses are due to hail

50-80

Hail

pieces of ice ranging in size; largest in the US was 8in in diameter

Lightning 

electrical discharge between 2 charge centers; 80% of lightning occurs within the cloud itself

thunder can only be heard about ___ miles away under good conditions

12

Tornadoes

violently rotating column of air that forms from a cumuliform cloud (primarily develop within supercells)

Widest tornado path

El Reno 2013, 2.6 miles wide

Deadliest tornado

2011 Joplin, MO, 158 lives

Climatology

75-90% of all tornadoes worldwide occur in the US

Fujita scale

developed by Theodore Fujita, relates the degree of damage to the intensity of the wind

Enhanced Fujita Scale

updated version of the F scale created by a team of meteorologists and engineers because the original scale was not scientific enough

Tornado watch

conditions are favorable for tornado formation (a tornado COULD form)

Tornado warning

a tornado has actually been observed by a trained spotter or doppler radar

Tornado fatalities

trend has decreased drastically since 1920s due to early warning, better construction, improved education, and better medical care (NOT because tornado patterns have changed)

What percent of fatalities were F2 tornadoes responsible for?

98.8%

Why is the trend in fatalities moving east?

the eastern states are more populated and have higher poverty rates meaning they are more vulnerable to deaths (generally more people there to die)

Nocturnal tornadoes

difficult to spot, people are sleeping = only 27% of tornadoes are nocturnal but 40% of fatalities are due to nighttime tornadoes

Trend in nocturnal tornado deaths

trending upward simply because population size and poverty is increasing

What is the issue with some parts of the country having uniform tornado probability year round?

“persistent, low risk = complacency”; always being told to be careful eventually causes people to let their guards down

Issue with visibility

due to forest cover and humidity you can’t always see when a tornado is forming which leads to more fatalities

____% of fatalities occur in MHs but only make up ____% of housing stock

50, 8

Trend in fatalities in mobile homes

increased from 37% to 5% because the housing market is so bad and mobile homes (which are more dangerous), are more affordable

Housing density

mostly concentrated in the east, very high in the south east which is why tornado deaths are highest there

Changing landscape

tornadoes are not changing enough to justify the intense impacts, everything is changing including land use and population expansion which causes larger disasters

Is there a trend in severe weather and tornadoes?

the evidence is not exactly conclusive and does not point to there being more storms, tornadoes are difficult to study so the evidence is messy

Tornado outbreaks

fewer overall tornado days per year but more of those days have 30+ tornadoes reported (could be due to reporting bias)

What happens to tornado occurrence when you change risk AND exposure?

threefold increase in annual tornado impacts and disaster potential from 2010 to 2100

Why are tornadoes more likely in the mid south?

high hazard risk, population density, manufactured homes, nighttime events, socioeconomics, complacency, education…

Warning complexity

a warned event does not necessarily mean a successful event because people might not react to the warning; there are also false alarms, complacency, and issues with credibility

Credibility

extremely important to effective warning communication, the initial siren has lost credibility which causes fewer people to respond to it

4 knowledge bases

-scientific/ experimental

-personal experience (lessons learned)

-revelation (best practices)

-intuition (seems like a good idea)

Warning myths

1. panic (warnings will cause panic)

2. short warnings (they must be short to be understandable)

3. cry wolf (people won’t listen to future warnings if past have been false)

Public warning challenge

individual perceptions often do not align with reality, many people don’t perceive risk, there is optimism bias and denial/ avoidance preventing people from believing a hazard will occur

3 topics vital to maximize warning effectiveness

1. source (should be credible)

2. content (tell people exactly what to do and when, who exactly should act and also the consequences of not acting)

3. style (should be clear, specific, certain, accurate, and consistent)

Solutions to hazards and disasters

very complicated problem; there are always caveats but in general there should be an adoption of local and regional planning policy, enforcement and updating of building codes, and community planning