Severe and Unusual Weather Exam 3

Thunderstorm

A cloud or collection of clouds (cumulonimbus) that produces lightening and thunder.

LIGHTENING because it is needed to create thunder.

What is the key ingredient that defines a thunderstorm?

$2.4 billion

What is the $ of U.S. damage of lightening, hail, wind, and tornadoes?

1. Threaten lives

2. Threaten property from wind and hail

How does the NSW reserve the term "severe" thunderstorms?

It has to have the potential for 2 things?

1. Wind damage

2. Gusts 58mph or greater

3. 1'' hail or larger

How does the NSW reserve the term "severe" thunderstorms?

Must have 1 of the following

3 Options

1. Moisture in lower to mid levels of atmosphere

2. A mechanism to trigger updraft

3. Unstable Air Mass

All thunderstorms require 3 things:

1. Vertical Wind Shear

All thunderstorms require 3 things.. however severe thunderstorms require 1 additional requirement?

Large bodies of water

The first ingredient for a thunderstorm is: WARM, MOIST AIR

Typical sources of moisture are .....?

Differential Surface Heating

The second ingredient for a thunderstorm is: *LIFTING MECHANISM*

- Sunlight warms the Earth's surface. The heating is not uniform.

-The warmest air rises due to convection and produces cumulous clouds

Topography

The second ingredient for a thunderstorm is: *LIFTING MECHANISM*

- As air encounters a mountain it is forced up the slope of the terrain.

-Upslope thunderstorms are common in the Rocky Mountain west during the Summer

Fronts

The second ingredient for a thunderstorm is: *LIFTING MECHANISM*

- If the air ahead of a cold front dry line is moist and unstable, thunderstorms will form along the front.

Outflow Boundaries

A result of the rush of cold air as a thunderstorm moves ahead.

RISE and RISE

The third ingredient for a thunderstorm is: UNSTABLE ATMOSPHERE

- A lifting mechanism forces air to ....., if it is unstable it will continue to .... when given a nudge upward.

Soundings

Graphs representing the vertical profile of the atmosphere. The data used to create these come from radiosonde measurements.

DALR

Air that is initially UNSATURATED rises and cools at the ...?

Direction or Speed

The fourth ingredient for a thunderstorm (must be severe) is: VERTICAL WIND SHEAR

Change in wind ...... or ..... with heigh

WITHIN

WITHOUT Vertical Shear precipitation develops ..... the cloud

Warm, moist air

WITHOUT Vertical Shear precipitation and downdraft takes over the cloud and cuts off the supply of .........

Updraft

WITH Vertical Shear precipitation is transported away from the .....?

Updraft

Stream of rapidly rising air within a thunderstorm.

CLOUD

Updraft is the reason we have a ...?

Anvil

-A fat cloud formation at the top of a storm.

-Created when the updraft hits the tropopause and spreads out laterally.

Has a strong updraft

If anvil is thick?

Has a weak updraft

If anvil is thin?

Ice Crystals

Extremely cold temps in the upper troposphere mean that the anvil is composed of ...?

Overshooting Top

"Bubble" of cloud that sticks above the anvil.

Forms when the updraft overshoots the anvil.

Mammatus Clouds

"Pouches" of clouds that hang down from underneath anvils.

Occur after the worst of thunderstorms have passed.

Downdraft

Stream of descending air within a thunderstorm.

Downdraft

The ...... is associated with precipitation

1. Falling Precipitation drags cold air down to the surface.

2. Some of the precipitation melts.

3. Some of the precipitation evaporates/sublimates

3 Downdraft Contributions

Downburst

Downdrafts that are strong enough to cause damage to the ground.

Outflow

Cold air that develops under a thunderstorm

Associated with a downdraft.

Gust front

Boundary between the cool outflow air mass and the warm mass feeding into the storm.

Shelf Cloud

Cloud that extends below the base of the storm and forms along gust front.

Shelf Cloud

Official name: Arcus cloud

A wedge-shaped appearance. A strong gust front can cause the leading edge of a shelf cloud to appear "ragged"

Roll Cloud

Cloud that forms along gust front, tube-like

Detached from the base of the cumulonimbus cloud

Hail

The precipitation of a ball of chunk of ice.

It forms in thunderstorms with strong updrafts.

Vivian, South Dakota

Largest US Hail?

Bangladesh

World's largest hail?

1. Hail growth in laboratory win tunnels

2. Launch balloons into thunderstorms

2 different types of Hail Research

1. strong updraft

2. hail embryo

2. Lots of supercooled water

What are the 3 requirements for hailstone growth?

Hail embryo

An ice particle that occupy the center of a hailstone and serves as a core for their initial growth.

Water that is colder than 32 degrees Fahrenheit, but remains unfrozen

How cold does the water have to be to be "super cooled" water for hail formation?

Supercells

The largest hailstones form in ...?

Hail

If the preciptation cascade from a storm looks like "tendrils", its composed of ...."

Lightning

..... occurs to equilibrate a charge imbalance in the atmosphere

The stepped leader forms

- Channel of negative charge from cloud

Step 1 of lightning

Streamers form

- + charge that reaches up to approaching charge

- tries to connect with stepped leader

Step 2 of lightning

Streamers & Stepped Leader connect

- + and - charge connect

Step 3 of lightning

The discharge

- conductive current between cloud and ground

- charge flows downward from cloud

+ charge flows upward from ground

- Return stroke is what we see

- Travels from the ground to the sky

Step 4 of lightning

Their tops are closer to the base of the storm clouds.

Why do tall objects get struck more frequently?

Dart Leader Forms

-Occurs if electrical potential remains, another leader, called the dart leader propagates to the ground.

Not branched

Doesn't occur in steps

Step 5 of lightning

Streamer Forms

- A streamer extends up from old channel

Step 6 of lightning

Streamers and Dart Leader Connect

- and + charge connect

Step 7 of lightning

The Discharge (2nd return stroke)

-conductive current between cloud and ground

Step 8 of lightning

Bolt from the Blue

is a cloud to ground lightning flash which typically comes out of the back side of the thunderstorm cloud, travels a relatively large distance in clear air away from the storm cloud, and then angles down and strikes the ground.

Thunder

The sound lightning makes

5 seconds to travel one mile

How long does it take to hear thunder?

Refract

The difference in speed causes the sound wave to .... toward the COOLER AIR.

Direct strike

A person struck directly by lightning

Side flash

Occurs when lightening strikes a taller object near the victim and a portion of the currents jump from a taller object to the victim.

Ground Current

When lightening strikes a tree or other object, much of the energy travels outward from the strike in and along the surface.

Conduction

Lighting can travel Long distances in wires or other metal surfaces.

Males

Males or females or more frequent lightning victims?

Tropical Cyclones

-Low pressure systems that begin as a collection of unorganized thunderstorms.

-They form over tropical or subtropical waters and eventually evolve into a highly organized cyclone.

-DO NOT have weather fronts associated with them

Tropical Disturbance

Wind = 0 to 22mph

- is a tropical weather system of unorganized thunderstorms that maintains its identity for 24 hours or more.

Tropical Depression

Wind= 23 to 38 mph

Tropical Storm

Winds= 39 to 73 mph

Eye

Where do you find the lowest pressure of a hurricane?

The outside edges of the hurricane

Where do you find the highest pressure of a hurricane?

Eyewall

Where are the fastest wind speeds in a hurricane.. this is the location with the large pressure gradient.

1. Warm ocean water

2. Weak Vertical Wind Shear

3. Unstable Atmosphere

What are the ingredients for a hurricane?

For warm air to rise and create area of low pressure

1st Ingredient of Hurricane: Warm Ocean Water

Why do we need warm water?

To keep air accelerating upward to form thunderstorms

2nd Ingredient of Hurricane: Unstable Atmosphere

Why do we need an unstable atmosphere?

To let storm grow

3rd Ingredient of Hurricane: Vertical Wind Shear

Why do we need vertical wind shear?

Storm Surge

Rapid rise in sea level that occurs as a hurricane approaches a coastline

1. Hurricane sucks up the water into the low pressure center

2. Strong winds pushing and piling up water

What 2 things cause a storm surge?

Northeast Quadrant

Storm surge is highest in the .... quadrant that the hurricane is moving>

Rotates

A key difference between supercell thunderstorms and all other thunderstorms is that the updraft ......?

Mesocyclone

What is the rotating updraft called?

Rain-free base

You can identify the location of a mesocyclone by looking for what is known as a ......... This is a non-precipitating cloud base that forms beneath the updraft.

Wall Cloud

an isolated cloud lowering attached to the rain-free base of a thunderstorm

SOUTHWEST

The wall cloud is usually located in the .... portion of the storm

2

How many downdraft do supercells have?

Forward Flank Draft

The FFD is the main downdraft of the supercell. It is the downwind of the updraft and the rain-free base.

What is FFD?

Rear Flank Draft

The RFD is an area of descending air that occurs behind the updraft.

What is RFD?

Flanking line

a line or row of towering cumulous clouds leading up to the main updraft tower.

Tornado

Violently rotating column of air

-in contact with the ground

-extend downward from a cumulonimbus cloud

Funnel Cloud

Condensation Cloud

-extends from a deep convective cloud

-associated with a rotating column of air

-NOT in contact with ground

Dust Swirl

Created when you have rotation at the ground and those winds kick up dirt and debris.

- Intense low pressure

- Strong pressure gradient is what is responsible for extreme damage

2 Characteristics of a Tornado

Counter-clockwise

What direction does a tornado spin?

SW to NE

What direction does a Tornado travel?

Storm Spotters

Provide ground truth on observations from radar, satellites, and reporting stations.

Radar and Doppler Radar

How do you detect a tornado?

HOOK ECHOS

TORNADO

Not all ..... contain a tornado.

Not all ..... produce a hook echo.

Fujita Scale

-Uses the damage associated tornadoes

-Estimates wind speeds

Tornado WATCHES

-Issued by NWS when conditions are favorable for severe thunderstorms to produce tornadoes in and close to watch area

Tornado WARNINGS

Issued by NWS when a tornado has been sighted by a storm spotter or indicated on radar.