Week 5: Severe weather

The earths energy balance

There is an equilibrium between incoming radiation and outgoing radiation

* Earth intercepts only a small portion of the suns radiation

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The Sun’s energy drives the hydrologic cycle and all weather phenomena on Earth.

* nearly all of the energy available at earths surface comes from the sun

The atmosphere

It is composed of __***nitrogen (78%***____)__ and __***oxygen (21%)***__

* the remaining 1% consists of water vapour, carbon dioxide, and other ‘trace’ gases

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water vapour in the atmosphere can result in cloud development and the formation of precipitation

* water vapour comes from evaporation from the oceans

Structure of the atmosphere

All weather (i.e., clouds and precipitation) id confined to the troposphere

* the ozone layer (25km) above the surface) protects us from the sun’s harmful UV rays; it is found in the stratosphere

Clouds

Cloud names generally contain a prefix and a suffix.

* The **prefix** describes the **height** of the cloud
* the **suffix** describes its **appearance.**

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**Prefixes:** **Suffixes:**

High cloud: cirro- Puffy: -cumulus

Mid-level cloud: alto- Flat: -stratus

Low cloud: strato-

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Ex:

“nimb” clouds

Clouds that produce precipitation contain “nimb” in their name.

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__**Cumulonimbus**__

* A cloud that produces lightning, thunder, and heavy rain

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__**Nimbostratus**__

* A cloud that produces prolonged precipitation

Fronts

A front marks the boundary between two air masses.

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The name of the front describes the type of air __**behind**__ that front.

* at a cold front, dense cold air undercuts warm air
* at a warm front, the less dense warm air overrides cold air.

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**image:**

blue line = cold front

red line = warm front

Thunderstorms

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what 3 things does a thunderstorm need?

At any moment, there are approximately 2000 thunderstorms occurring on Earth.

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Thunderstorm development

requires:

* unstable environment (a steep vertical temperature gradient)
* water vapour
* rising air (or a lifting mechanism, eg., **a front**)

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image:

* days per year with thunderstorms

Thunderstorm development

they develop in 3 stages:


1. cumulus
2. mature
3. dissipative

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\*most storms pass through all the stages in 1 hour

Cumulonimbus

* hot air + cold air
* hot air rises until it hits the statosphere
* cold air pushing down
* rain is where the cold air is

Hail formation

It is formed during thunderstorms in cumulonimbus clouds

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Updrafts in the cloud repeatedly force a water droplet upward

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The droplet develops a ring of ice around it each time it enters the cold part of the cloud.

Hail

The ball oof ice eventually becomes heavy enough to fall to the surface

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hail stones are measured against everyday objects

* Hail the size of basketballs killed 25 people

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image:

* China (2002)

Lightening

Definition:

* **a spark of electricity occurring in a cloud**

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Most lightning strikes are within the cloud.

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Lightning heats the air causing the air to expand thus creating a shockwave (thunder).

* sometimes the atmosphere refracts thunder making it inaudible

Cases of lightening

What is the main requirement for lightning?

* a cumulonimbus cloud containing a region of opposite charges

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The interaction of ice crystals, hailstones, and water droplets result in a separate distribution of charges in the cloud.

Tornado

Definition:

A rotating column of air touching the ground that formed within a supercell thunderstorm.

* a rotating column not touching the ground is called a funnel cloud

Characteristics of tornadoes

On average they are approximately 300 metres wide.

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They travel from the southwest toward the northeast at an average speed of 50 km/h.

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they tend to exist for less than 30 minutes with a defined life cycle

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The most common season for tornadoes is summer in Canada and Spring in the U.S.

Tornado life cycle (3 stages)

Tornadoes exist in three defined stages:

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__**Organizational Stage**__

* Wind shear causes rotation to develop
* funnel cloud protrudes from above
* dust and debris rotate beneath

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__**Mature Stage**__

* most severe damage occurs at this stage

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__**Rope Stage**__

* the tornado stretches out and weakens

Wind shear

a change in wind speed or wind direction over a distance

Classifying Tornadoes

Enhanced Fujita Scale:

Tornadoes are classified on a scale of EF0 to EF5, based on the damage produced.

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EF5 tornadoes:

* complete devastation; wind speed over 322km/h
* less than 1% of tornadoes are classified as EF5

Tornado Alleys

The U.S. experiences the most tornadoes on Earth.  Canada experiences the 2nd most.

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United States Tornado Alley

* Kansas and Oklahoma

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Canada Tornado Alley

* Southwestern Ontario

Why do tornado alleys exist?

* They are areas where air masses commonly collide


* they are areas of relatively flat land (this allows for undisturbed rotation)

Canada’s Tornado Alley

Tornadoes in Ontario occur when a southwesterly wind brings warm, moist air from the Gulf of Mexico.

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The warm, moist air often interacts with cooler lake breezes.

Notable Tornadoes - Canada

April 3, 1974   “Super Outbreak”

On this day, 148 tornadoes touched down between Ontario and Alabama

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* 9 people died when a tornado destroyed the Windsor Curling Club.


* One of the strongest tornadoes in the outbreak killed 23 people in Guin

Notable Tornadoes - Worldwide

The largest tornado outbreak in world history occurred in 2011 from April 25th to April 28th.

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In the southeast U.S. 358 tornadoes touched down and 324 people were killed (239 in Alabama).

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Overall, more people were killed by tornadoes in 2011 than any other year since 1925.

Joplin Tornado

May 22, 2011

* An EF5 tornado killed 162 people in Joplin, Missouri
* This tornado was the costliest in U.S history ($2.2 B) and the deadliest in the U.S. since 1947

Goderich Tornado

A tornado in Goderich killed 1 person and

destroyed much of the town core on Aug. 21, 2011.

* it was the first EF3 tornado to touch down in Ontario in 15 years

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The tornado was spotted over Lake Huron on RADAR and a warning was issued 12 minutes before it reached the town.

Moore Tornado

On May 20, 2013 an EF4 tornado in Moore, Oklahoma killed 24 people.

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Advances in weather technology have greatly improved warning systems over the past decade.

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A tornado warning was issued for the area 16 minutes in advance

Tropical cyclones

These form over warm water at latitudes 5-20°.

They include tropical depressions, tropical storms, and hurricanes.

* they contain high winds, heavy rain, storm surges

Extratropical cyclones

These form over land or water in temperate regions at latitudes 30-70°.

They are associated with fronts and are also called mid-latitude cyclones.

* They contain rain, snow, freezing rain, etc.

Tropical cyclone development

(ranked in order of severity)

4. __**Tropical Disturbance**__

* A large area of low pressure with unsettled weather

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3. __**Tropical Depression**__

* Un organized area of thunderstorms

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2. __**Tropical Storm**__

* An organized area of storms with wind of 65-119 km/h

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1. __**Hurricane**__

* An area of low pressure with wind of at least 120km/h

Tropical cyclones around the world

They are referred to by different names in different parts of the world.

* they require a water tempurature of at least __**26 degrees**__

Components of hurricanes

**Eye**

* A region in the centre with light winds and clear to partly cloudy skies

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**Eye wall**

* A ring of intense thunderstorms that whirl directly around the eye.

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**Spiral Rain Bands**

* Rings of tall clouds and heavy rain that exist throughout the hurricane

Anatomy of a hurricane

Naming hurricanes

Names were first assigned to hurricanes in 1953.

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Alternating male and female names are used in alphabetical order (5 letters are skipped)

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The name is retired if the hurricane produced notable damage.

* Ex:
* Andrew, Katrina

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Names were exhausted for the first time ever in 2005 when 27 hurricanes occurred and for the second time in 2020.

* when the list of names is exhausted, the remaining storms are named after the letters of the greek alphabet (in order).

Hurricane Movement

Hurricanes typically travel very slowly (less than 20 km/h).

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Because wind in a hurricane rotates counter-clockwise, wind speed varies over the area of the hurricane.

__**Examples midterm question:**__

If a hurricane is moving to the northwest, where will its highest winds be located?

1. draw arrow pointing Northwest
2. Remember hurricanes rotate __**counter clockwise**__
3. draw a circle with arrows going counterclockwise
4. match up the arrow with original direction of movement

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\*see camera roll for example

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* weakest winds - opposite direction

Storm surge

__**It is the most devastating effect of hurricanes**__

It results from powerful winds creating an abnormal rise in sea level.

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Hurricane Andrew (1992):

* 23ft storm surges were reported in Florida

Classifying hurricanes

Hurricanes are classified by the Saffir-Simpson scale

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The classification is based on wind speed

Regions at risk

In North America, areas at highest risk are found along the Atlantic coast and the Gulf of Mexico coast.

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\*The official hurricane season ranges from June 1st to November 30th

(remember hurricanes feed of warm water)

Many hurricanes occur in August and early September because this is when the water is warmest.

Hurricane Katrina

Hurricanes in Canada

Hurricane Fiona:

* Sep. 24, 2022
* caused 2 deaths and was a category 2 hurricane when it made landfall in Nova Scotia

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Hurricane Hazel:

* Oct. 15, 1954


* It killed 81 people when intense flash floods in Toronto swept away homes; no other natural disaster has caused that many deaths in Canada to this day.
* flooding of the Humber river caused the most damage

Fog

It is a cloud with its base at the Earth’s surface that reduces visibility.

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It occurs at night when the air cools to the dew point (at which point water vapour condenses into droplets)

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Fog

Snowstorms as hazards

The worst natural disaster in Detroit in terms of death toll was a snowstorm in 2003.

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The storm resulted in the deaths of 36 o people from heart attacks while shovelling snow

Blizzards

They are intense winter storms with very specific conditions:

* wind of at least 40km/h
* snow falling or blowing snow occurring
* visibility less than 400m
* all of these must occur for at least 4 hours

Lake effect snow

Snowbelts are found downwind of the lakes (in winter, the wind is often from the northwest)

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Lake effect snow is caused by cold air moving over relatively warm water.

→ heavy snow falls downwind of lakes

Lake effect snow in Southern Ontario

London and Kitchener frequently receive lake effect snow from Lake Huron causing high annual snowfall.

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Windsor occasionally receives lake effect snow from lake Michigan

Lake effect clouds

Southern Ontario frequently experiences lake effect clouds in Winter.

* both lake effect clouds and lake effect snow diminish when the lakes freeze (this can occur by feb)

Haboobs

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what causes it to form?

These are sandstorms that occur

in arid and semi-arid regions.

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What causes a haboob to form?

* downdrafts on the leading edge of a thunderstorm

Dust devils

Definition:

* a small spinning vortex of air formed over hot, dry land

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What causes a dust devil to form?

* as hot air rises, the wind direction may change due to obstacles
* this may result in a spinning column of air

Ice storms

These are mainly caused by freezing rain.  The weight of the ice can pull down trees and power lines.

Droughts

This is an extended period of unusually low precipitation.

* droughts affect more people in North America than any other hazard

They cause water shortages that can lead to crop failure.  In developing countries, this may lead to malnutrition and famine.

* droughts are linked to global weather patterns and are a normal part of the climate system

Wind chill & humans

Wind chill is a correction factor to a temperature reading caused by the presence of wind making the air feel cooler than the temperature suggests.

Humidex & humans

Humidex is a correction factor to a temperature reading caused by high levels of humidity making the air feel warmer than the temperature suggests.

Minimizing severe weather hazards

Forecasting has improved dramatically with better technology; 3-day forecasts are very accurate today.

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Weather satellites detect cloud cover and aid in forecasting hurricanes and mid-latitude cyclones.

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RADAR detects precipitation (both the type of precipitation and intensity)

Hazardous weather

The most important job of a forecaster is to alert the public of potentially dangerous weather.

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Alerts are broken into three categories:

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1. __**Watch**__
* an alert covering an area
* eg. tornado watch, winter storm watch
2. __**Warning**__
* An alert that usually covers smaller areas. It indicates that hazardous weather is currently occurring in the area
* eg. severe thunderstorm watch
3. __**Advisory**__
* used to alert the public of less hazardous weather conditions
* dense fog advisory

Watch:

Watch:

An alert covering a wide area.

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eg.

Warning

An alert that usually covers smaller areas

eg.

Advisory:

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eg.

What atmospheric layer contains all weather?

troposphere