Chapter 10: Tornadoes, lightning, heat and cold

Hypothermia

Deadly condition when the body temo drops below 35degrees celsius

Strong cold winds > 56km'/hr with blowing/falling snow

Blizzards

freezing rain

large volumes of supercoole rain that freezes on impact

Thunderstorms

Tall, buoyant clouds of rising moist air

3 mechanisms that develop thunderstorms

Convection: surface heated air rises buoyantly, cloud forms locally

Fronts: air masses collide at fronts, warmer air rises forming clouds

Orographic: air mass flows up steep slope, expands and cools increasing relative humidity to form clouds

How does condensation help in the creation of thunderstorms?

Condensation forms Cumulus clouds, heat released to power severe weather
Cumulonimbus clouds can build up to 20km high

When are thunderstorms categorized as severe?

When: Winds> 93 kmph

Hail diameter > 25mm

Supercell thunderstorms

These are violent sever thunderstorms with huge updrafts
20 to 50km rotating mass or mesocyclone
Vortex is rotating updraft about vertical axis

Where are thunderstorms common in the US

In central and southern states caused by the warm moist air moving coming from the Gulf of Mexico hitting the cold air masses moving from the north

What is Hail?

Layered ice balls dropped from storms with:

Buoyantly rising hot, moist air

Upper-level cold air creating large temp contrasts

Strong updrafts keeping hailstones aloft while adding layers

What are Tornadoes?

Rapidly rotating column of air from large thunderstorm
highest wind speeds of any weather phenomenon
About 70% of earth’s tornadoes occur in Great Plains of Central US
Travel up to 100km/hr, wind speeds can exceed 500 km/hr

How tornadoes form?

3 Air masses moving in different directions meet and give shear to thunderstorm.
—Warm, humid, low Gulf of mexico air

—Cold, dry, mid-altitude Canadian or Rocky Mountain air

—Fast, high altitude jet stream winds

What is the Corkscrew effect?

This is when rising gulf air is spun one way by mid-altitude cold air then spun another way by jet stream.

What are wall clouds?

This is where powerful tornadoes can emerge

What is hook echo?

This is a high reflectivity area in radar image shaped like a hook, indicator of tornado potential

Vortex scale

-Air mass collisions low in atmosphere create horizontal tube of air spinning parallel to ground
-Warm rising air provides vertical wind shear that lifts the spinning tube of air.
-can rise to mesocyclone status

During what year did 3 of the 5 biggest tornado outbreaks in histoy occur?

It occured during a 6-week period in April and May of 2011
-Deadliest outbreak happened between Apri 25 to 28

-Second deadliest outbreak happened about a month earlier sometime between May 21 - 27

How does the flow of electric current for lightening work?

-flow of electric current: top of clouds have excess positive charges seeking balance with the bottom of the clouds’ excess negative charfes

-Charge imbalance from freezing and shattering of super cooled water drops - charge separations distributed by updrafts and downdrafts during early cloud buildup

-Negative charges in basal portion of cloud interact with the ground, attracting positive chages on the ground surface

-Lightening moves from cloud to ground, ground to cloud or from cloud to cloud—The Triple Lightning Modes.

what has been the biggest killer of all severe weather phenomena in US for the past 30 years?

Heat.

Lightning Bolt formation

How many heat related deaths occured in Chicago July 1995.

-465 heat-related fatalities in Chicago
-Half who died lived on top floor

what is Urban heat Island in City Weather?

Cities are warmer than surrounding hinterlands, up to 10 degrees C at night