Severe Storms

Almost all hazard events occur…

In combination with or cause other hazards and have complex interactions with each other and human aspects

Aggregate multi-hazard

The accumulation of impacts from multiple independent hazards, hazard events may be unrelated but occur sequentially in the same area or occur simultaneously in different locations with concurrent impacts

Cascading multi-hazard

Events where one hazard triggers other hazards (hurricane Harvey produced inland flooding, flooding disrupted power and triggered chemical spills)

Compound multi-hazards

The interaction of hazards which may include single extreme events, multiple coincident and sequential events, these events are correlated in space and/or time but result from distinct causal pathways. (example: e.g. St Vincent responding to the COVID-19 pandemic then having to evacuate and shelter the populationfrom1/3ofthe island due to the La Soufrière volcano eruption. Since these hazard interactions may be distant in space and time, operate on multiple spatial and temporal scales, and affect communities differently, compound multi hazards is conceptually and computationally the most difficult approach to employ.)

Multi hazards caused by tropical storms

Wind, rain, storm surge, coastal erosion, flooding, landslides, saline intrusion, building damage, agricultural losses, transport disruption

Multi hazards caused by tornadoes

Wind, pressure drop, updrafts, building damage, agricultural loss

Multi hazards caused by hailstorms

Lightning, building damage, agricultural loss, hail

Multi hazards caused by Winter cyclones

Flooding, landslides, coastal erosion, building damage, agricultural loss

Multi hazards caused by snowstorms

Glaze, wind, blizzards, transport disruption, building damage, agricultural losses

Characteristics of thunderstorms

Lightning, thunder, strong winds, heavy rain (sometimes), snow, sleet, hail

What cloud generates thunderstorms

cumulonimbus

Where are thunderstorms most frequent

middle latitudes (mixing of moist and cool air)

What are the three stages that create a thunderstorm

Developing stage, mature stage, dissipating stage

Developing stage of thunderstorm

Warm moist air moves upward in an updraft (mountain, cold front), puffy cumulus clouds may form in atmosphere. The moisture in the air condenses into water droplets as it rises. The cloud will continue to grow as long as warm air from below continues to rise.

The mature stage of thunderstorms

As the cumulus cloud continues to grow, the tiny water droplets within it grow larger as more water from the rising air is added to the droplets. The cloud starts to look dark and gray as more water is added to it, and the growing droplets that make up the cloud begin to get heavy. Raindrops start to fall once cloud reaches dew point. Meanwhile, cool dry air flows downward in the cloud, called a downdraft, pulling water down as rain. The cycle of the updraft, downdraft and wait make the could a cumulonimbus cloud which is also called a thunderstorm cell. The moving air builds electrical charges creating lightning

The dissipating stage of a thunderstorm

The downdrafts in the cloud become stronger than the updrafts, the storm starts to weaken, since warm moist air can no longer rise, cloud droplets can no longer form. The storm dies out with light rain as the cloud disappears from bottom to top. The whole process takes about one hour for an ordinary thunderstorm

Two thunderstorm types

Single-cell and multi-cell cluster, multi-cell lines, supercells

Single-cell thunderstorm

One main updraft, typical form in many temperate locations, also occur in cool unstable air that often follows the passage of a cold front in winter

Multi-cell cluster thunderstorm

Often form from convective updrafts in or near mountains and linear weather boundaries such as cold fronts, mature thunderstorms are found near the centre of the cluster, while dissipating thunderstorms exist on their downwind side, most common type

Multi-cell line thunderstorms

A line of thunderstorms that can form along a cold front, the squall line contains heavy precipitation, hail, frequent lightning, strong straight-line winds

Supercell thunderstorms

Large quasi-steady-state storms that form where wind speed or wind direction varies with height, separate downdrafts and updrafts, strongest and most severe (80% of these form destructive storms), strong link to tornado formation

Thunderstorm hazards

Lightning, hail, tornadoes, flash floods & debris flows (difficult to predict), downdrafts (high velocity winds)

Tornado definition

A rapidly rotating column of air that is in contact with both the ground and cumulonimbus cloud

Where do tornadoes occur

middle latitude (most occur in US)

Characteristics of US that make good tornado conditions

Low-pressure systems in the US pull warm moist air from the gulf of Mexico and cool dry air from the Rocky Mountains or the high desert in the southwest. The states that fall between those regions end up being the ideal location for severe weather and tornadoes

How are tornadoes formed

The updraft in a supercell begins to spin as it rises due to wind going in different directions, increasing rainfall drags with it an area of quickly descending air known as the rear flank downdraft (RFD). As the downdraft accelerates, it drags the supercell’s rotating mesocyclone toward the ground

Life cycle of a tornado

Increasing rainfall drags down the RFD, Downdraft accelerates as it approaches the ground and drags the supercell’s rotating mesocyclone towards ground, as mesocyclone lowers it takes in cool, moist air from the downdraft region of the storm, the convergence of warm air in the updraft and cool air causes a rotating wall cloud to form, as the updraft intensifies, it creates an area of low pressure at the surface, this pulls the focused mesocyclone down, in the form of a visible condensation funnel, as the funnel descends, the RFD also reaches the ground, fanning outward and creating an intense gust of wind

What is the tornado intensity scale

Fujita intensity scale (created 1973 and modified 2007)

What are wind speeds for EF0 tornadoes

65-85 mph

What are wind speeds for EF1 tornadoes

86-110 mph

What are wind speeds for EF2 tornadoes

111-135 mph

What are wind speeds for EF3 tornadoes

136-165 mph

What are wind speeds for EF4 tornadoes

166-200 mph

What are wind speeds for EF5 tornadoes

>200 mph

What is the most common intensity of tornadoes in the USA

EF0 or EF1 (80%)

What damage can be caused by a EF0 tornado

Little to no damage to man-made structures, breaks branches off trees pushes over shallow rooted trees

What damage can be caused by a EF1 tornado

Beginning of hurricane wind speed, peels surface off roofs; mobile homes pushed off foundations or overturned, moving vehicles pushed off road, moderate damage

What damage can be caused by a EF2 tornado

Considerable damage, roofs torn off of frame houses, mobile homes demolished, boxcars from trains overturned, large trees uprooted or snapped, light object missiles generated

What damage can be caused by a EF3 tornado

Roof and some walls torn off well-constructed houses, trains overturned, most trees in forest uprooted, heavy cars lifted and thrown

What damage can be caused by a EF4 tornado

Well-constructed houses leveled, structures with weak foundations blown away some distance, cars thrown and large missiles generated

What damage can be caused by a EF5 tornado

Strong frame houses leveled off foundations and carried considerable distances, automobile-sized missiles fly through the air in excess of 109 yards, trees debarked, steel reinforced concrete structures badly damages, complete devastation

How many tornadoes in the US each year

1,000

About how many tornado related deaths in the US each year

80

How many tornado related injuries in the US every year

1,500

Largest single tornado event

March 1925 “tri-state tornado”

What was the magnitude of the “tri-state tornado”

EF5

How many deaths were caused by the “tri-state tornado”

700

Where did the “tri-state tornado” occur

Missouri, Illinois, and Indiana

How many injuries were caused by the “tri-state tornado”

2,000

How much money in damages was caused by the “tri-state tornado”

$US 2.9 Billion

What were most injuries caused by during the “tri-state tornado”

Airborne debris

When and what was the most extensive tornado outbreak

The 2011 Super Outbreak in the SE USA

How many tornadoes were created during the 2011 Super Outbreak

360 confirmed tornadoes (224 of them within a single 24-hour period)

What hazard adaptation is little to no use for tornadoes

Altered land use planning (because tornadoes move)

What adaptations can you implement for tornadoes

Hardening structures (stronger buildings, shelters)

Issues with dispersing warnings for tornadoes

Radar can detect signatures not actual tornadoes, the program SKYWARN trains citizens on how to spot tornadoes but only way to confirm is by eyesight making early warnings difficult

Where do winter storms occur

Deep middle latitude depressions, wave run up in coastal environments

Characteristics of winter storms

Gale-force winds and coastal flooding, usually only rate 1 or 2 on the Saffir-Simpson scale (still have destructive energy after penetrating inland), Snow and Ice

What will 5cm of snow do

Create serious disruptions to traffic

What will 15 or more cm of snow do

Universally disruptive, unploughed roads not drivable, cars and trucks will get stuck on ploughed roads

What will 30 or more cm of snow do

Will collapse some roofs and bring down powerlines

What does the impact of winter storms depend on

Infrastructure, societies with regular snowfall are better adapted and have fewer impacts compared to societies with irregular or episodic snowfall

Adaptations to heavy snowfall

Snowploughs, salt, road grit, snow tires, studded tires, chains on tires, keeping utilities underground (don’t freeze or collapse), reinforced roofs, previous experience (driving in snow)

What happens in an ice storm

Freezing rain or “glaze” events, defined as a storm with at least 0,25-inch of ice accumulates on exposed surfaces

Two paths for ice storms to occur

Ice is precipitated above a warm layer, melts and then freezes in a surface cold layer (sleet falls), or liquid droplets can continue to fall without freezing, passing through the cold air just above the surface, air cools below freezing but the drops themselves do not freeze (supercooling) until they hit the ground or trees, powerlines etc.

Freezing rain hazards

Treacherous surface, power lines snap or are pulled down, tree branches snap, power outages (cause hypothermia, CO poisoning)

What are the most pervasive hazards

Atmospheric hazards (everyone interacts with the atmosphere)

What are tropical cyclones

non-frontal, synoptic-scale, organized low pressure systems that form over warm oceans

Tropical cyclones also known as

Hurricane (Gulf of Mexico), Typhoon (NW pacific), Tropical cyclone (Indian ocean, Australia, SW Pacific)

How large can tropical cyclones be

10-100 Km wide

How far can tropical cyclones travel

about 500 Km a day and roughly 5,000 Km over storm lifetime

How long can tropical cyclones last

Days to a few weeks

Variables that influence the impacts of tropical cyclones

Strength, Landfall location, interactions with local topography, interactions with local climate, socio-cultural conditions

What is the issue with nomenclature surrounding tropical cyclones

The classifications of tropical cyclones vary greatly depending on where the event occurs. Makes it extremely difficult to compare events across the world

What is the classification system in the Western Hemisphere

Intensity classified according to windspeed, the Saffir-Simpson Hurricane Wind Scale (SSHWS), Based on one minute maximum sustained speed

How many categories does the SSHWS have

Five

What are the wind speeds for a category 1 Hurricane

74-95 mph

What are the wind speeds for a category 2 Hurricane

96-110 mph

What are the wind speeds for a category 3 Hurricane

111-129 mph

What are the wind speeds for a category 4 Hurricane

130-156 mph

What are the wind speeds for a category 5 Hurricane

>157 mph

History of the Saffir-Simpson Hurricane Wind Scale

Developed in the 1970s by Herbert Saffir (consulting engineer), and Robert Simpson (director of the National Hurricane Center), Scale is based primarily on wind speeds and includes estimates of barometric pressure and storm surge

Tropical cyclone hazards

Strong winds, heavy rainfall, storm surge, secondary landscape effects such as loss of electricity, flooding, debris, damage to trees and powerlines, contamination of drinking water

How are tropical cyclones created

Almost exclusively over tropical seas, winds moving in a circle around their central clear eye, with winds blowing counterclockwise in Norther Hemisphere and clockwise in Southern Hemisphere (Coriolis effect), Energy is derived through the evaporation of water from the ocean surface (it recondenses into clouds and rain when moist air rises and cools to saturation

What conditions have to be met for tropical cyclones to occur

Water temperatures at least 26.5ºC down to a depth of 50 m, Rapid cooling with height, which allows the release of the heat of condensation that powers tropical cyclones (latent heat of condensation about 450 cal/g), high humidity is needed especially in lower-to-mid troposphere, Low amounts of wind shear are needed (high amounts are disruptive), Need to be offset from equator by 5 degrees allowing the Coriolis effect to deflect winds blowing towards the low pressure centre and creating circulation, Low latitude and low level westerly wind initiate disturbances

How do tropical cyclones travel

Steered by local adjacent winds which makes tracking path somewhat predictable

What is beta drift

Significant factor in the movement of tropical cyclones particularly in the Atlantic Ocean. Caused by the advection of the background potential vorticity field by the storm circulation. Causes cyclones to move poleward

Advection definition

Is the defined as the transport of a substance or quantity by the bulk motion of the substance (air in this case)

Potential vorticity

Key concept in fluid mechanics, absolute circulation of an air parcel enclosed between to isentropic surfaces

Isentropic definition

Having equal entropy

What are most deaths in tropical cyclones caused by

Storm surges

Example of tropical cyclone storm surges

1970 Bhola which killed up to 500,000 people in the Bay of Bengal, 2008 Cyclone Nargis, 138,000 people died in Myanmar

How high were storm surges in Hurricane Katrina

Over 9m in some areas with equates to category 5 (even though officially labeled a category 3)

How does the Hurricane severity scale complicate public perception

The scale is only tied to wind speed not rainfall or storm surge so residents may not have an accurate understanding of how dangerous the hurricane is

How many mm does the sea level rise with every 1 hPa pressure drop

10mm

Factors that influence storm surge

Atmospheric pressure, Storm intensity, storm size, Storm speed (open coast means greater surge), Angle of coast (perpendicular means greater surge), Shape of coastline, Width and slope of offshore (higher surge on wide, gently sloping shelves

Mitigation and adaptation methods for tropical cyclones

Insurance, sea walls, berms, leaving dunes in place, shelters, raised earth platforms, strengthen structures against wind, houses raised

What kind of countries usually have insurance for tropical cyclones

Mainly in MDCs

What percent of the most expensive disasters in the US were Tropical cyclones

80%

Characteristics of tropical cyclone forecasting and warning

Forecasting has made massive improvements; there are many services with technology that allows remote sensing and tracking that produce models and forecastable products