1. Be wary of the main storm hazards.
a. Thunderstorms can create many hazards to life and property:
lightning, tornadoes, hail, downpours and local flooding, and downburst
and gustfronts (we will learn about these in later vignettes).
2. Recognize thunderstorms, be able to identify thunderstorm components,
and explain how they evolve.
Looks like anvil or mushroom.Thick clouds. Sometimes a very large, rotating
single-cell thunderstorm forms, called a supercell Tstorm. They can cause
tornadoes, large hail, frequent lightning, heavy rain, strong wind
3. Explain how storms get their energy from the Sun.
a. Solar energy is absorbed at 3 different heights: thermosphere (top),
stratopause (middle) and earth surface (bottom).
b. Absorbed sunlight at ground changes to sensible heat (warms the
air) -> temperature increases.
c. Latent heat (evaporates water from lakes, etc) -> humidity
increases. 2 heat sources forms fuel storms.
4. Explain the main characteristics that make a supercell thunderstorm so
much nastier than a normal thunderstorm.
a. It has one rotating cell, and lasts 30+ minutes due to wind shear.
Windshear is from wind speed or direction changes with altitudes,
and it will continuously draw humid boundary air as fuel.
Mesocyclone is when the whole supercell storm rotates, and cloud
continues to spiral around the main updraft, forming the strongest
5. Be able to recognize thunderstorms in radar and satellite images.
a. Weather radar transmits a beam of microwaves into the
atmosphere, and "listens" for the faint echo of microwave energy
that bounces back off of raindrops. Heavier rain causes a stronger
echo, which is often coloured as yellow and red on radar displays.
The lighter rain is shown with the blues and greens. The radar
image below shows a number of thunderstorms producing spotty
heavy rain, with no rain (shown as black in this image) in between
b. On visible satellite photos of thunderstorms, you can often see the
shadow of the thunderstorm anvil that is cast on the lower clouds
or on the ground. The anvils (marking the tops of thunderstorms)
in the satellite image below are circled in red. 6. Describe the different types of lightning, how they form, and what
happens when they strike something.
a. Lightning forms because electrical charges build up in
thunderstorms, associated with the freezing and collision of cloud
droplets and ice crystals (called graupeln). When the electrical
potential (i.e., charge difference) between the cloud and ground
becomes great enough (a breakdown potential of 3 billion volts /
km is needed, for every km length of the lightning bolt), the air
b. Cloud-to-cloud (IC) lightening: occurs when voltage gradient
within a cloud, or between clouds overcomes electrical resistance of
c. Cloud-to-ground (CG) lightening: occurs when negative charges
accumulate in lower portions of cloud. Can be positive or negative.
Negative strikes are more frequent, come from cloud base. Positive
strikes are less frequent, come from anvil, primary cause of natural
7. Explain the behavior of downbursts and gust fronts, and identify their
associated cloud & dust features.
- ✦What: Downburst - cold (dense) air sinking.
- ✦Why: Tstorm can create dense air where rain falls; due
to •precipitation drag & •evaporative cooling.
- ✦Risks: Often invisible, but hazard to aircraft