Transcript Thunderstorms Tornados

April 23, 2014
The Nature of Storms
Warm-up Review from Hurricanes:
1) What does a hurricane need to form (list
the 5 things)?
2) What is the most dangerous impact of
Hurricanes
Save this and turn in at end of class with
the other questions you will answer later
The Nature of Storms
Thunderstorms and Tornados:
Objectives
•Identify
•
•
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•
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the processes that form thunderstorms.
Compare and contrast different types of thunderstorms.
Describe the life cycle of a thunderstorm.
Explain why some thunderstorms are more severe than
others
Recognize the changes in severe weather
Describe how tornados form
Thunderstorms
Thunderstorms
Thunderstorms form
within large
cumulonimbus clouds
(thunderclouds)
They most often occur
in spring and summer
seasons
Air-Mass Thunderstorms

Thunderstorms classified by:
* what caused the air to rise.
• air-mass thunderstorm - air rising because of unequal
heating of Earth’s surface within one air mass.
– Mountain thunderstorms occur when an air mass rises as
a result of orographic lifting (Orographic lift occurs when
an air mass is forced from a low elevation to a higher
elevation as it moves over rising terrain.
– Sea-breeze thunderstorms - extreme temperature
differences between the air over land and the air over water.
Frontal Thunderstorms

Frontal thunderstorms - advancing cold
fronts and, more rarely, warm fronts.
• Cold-front thunderstorms get their initial lift
from the push of the cold air which can
produce a line of thunderstorms along the
leading edge of the cold front.
• Because they are not dependent on daytime
heating for their initial lift, cold-front
thunderstorms can persist long into the night.
ANNUAL THUNDERSTORM DAYS
Thunderstorms
How Do Thunderstorms Form?
How Thunderstorms Form

Three conditions must exist.
1. Moisture in the air.
2. Mechanisms for lifting the air.
3. Instability in portion of the atmosphere
through which the cloud grows.
Moisture
Lift
Instability
Stages of Development

Thunderstorms have three stages:
 the cumulus stage,
 the mature stage,
 the dissipation stage.
• Stages classified by the direction in which
the air is moving.
Stages of Development
1. Cumulus Stage
– air starts to rise upward.
– moisture condenses into a visible
cloud
– release latent heat.
– Droplets coalesce and form larger
droplets
– fall to Earth as precipitation.
Stages of Development
2. Mature Stage
– Precipitation falls and cools the
air around it which becomes more
dense than the surrounding air, so
it sinks creating downdrafts.
– Updrafts and downdrafts form a
convection cell.
Stages of Development
3. Dissipation Stage
– Supply of warm, moist air runs
out.
– Downdrafts cool the area from
which the storm draws energy.
– Without the warm air, updrafts
cease and rain stops.
How Thunderstorms Form
Limits to Growth
The air in a thunderstorm will keep rising until:
1. It meets a layer of stable air that it cannot
overcome
2. The rate of condensation, which diminishes
with height, is insufficient to generate enough
latent heat to keep the cloud warmer than the
surrounding air
Where is the thunderstorm?
Thunderstorms
Produce heavy rains,
strong wind,
possibly hail,
lightning and in
severe cases a
tornado.
Less than 1% of
thunderstorms
produce tornadoes.
Section Assessment
1. Why does there need to be an abundant
source of moisture in the lower levels of
the atmosphere for thunderstorms to
form?
The moisture feeds into a
thunderstorm’s updrafts,
releasing latent heat when
it condenses.
Section Assessment
2. What is the main cause of thunderstorm
dissipation?
The downdrafts created by a thunderstorm
eventually cut off the flow of warm, moist
air into the storm. Without the warm
updrafts, precipitation can no longer form
and the convection stops.
Section Assessment
3. Identify whether the following statements are
true or false.
true Latent heat is crucial in maintaining the upward motion
______
of a cloud.
false Thunderstorms are more likely to develop along a warm
______
front instead of a cold front.
true
______ A mountain thunderstorm is an example of an air-mass
thunderstorm.
true
______ In the mature stage of a thunderstorm, updrafts are
roughly equal to downdrafts.
Lightning and Thunder
Lightning and Thunder
During a
thunderstorm,
areas of positive
and negative
charge build up.
Lightning and Thunder
Lightning is a
sudden spark as
particles jump to
opposite charge.
Lightning and Thunder
Lighting can be as
hot as the surface
of the sun (10,000
degrees
Fahrenheit)
Lightning and Thunder
The lightning causes
the air around it to
expand rapidly and
then cool back
down causing a
shock wave we hear
as thunder.
Lightning and Thunder
What travels faster?
Sound
Or
Light
Lightning and Thunder
Since sound travels
much slower than
light, usually you
see the lightning
before the
thunder.
Lightning and Thunder
To figure out how
far the lightning is
start counting
when you see the
lightning, then
divide by 5 when
you hear the
thunder.
Lightning and Thunder
Most lightning is “cloud-tocloud” and never reaches
the ground “cloud-toground.”
Lightning Rods & Fulgurite
Metal rods that are
grounded by wires
provide a low resistance
path for lightning into
the earth, which is a
poor conductor.
The fusion of sand particles
into root like tubes, called
fulgurite, may result.
What Should You Do In
Thunderstorms?
Tornados
Tornado
A rapidly rotating
column of air that
evolve through a series
of stages, from dustwhirl, to organizing
and mature stages, and
ending with the
shrinking and decay
stages.
Winds in this southern
Illinois twister
exceeded 150 knots.
Tornado Occurrence
Tornadoes from all 50 states of the U.S. add up to more than 1000
tornadoes annually, but the highest frequency is observed in
tornado alley of the Central Plains.
Nearly 75% of tornadoes form from March to July, and are more
likely when warm humid air is overlain by cooler dryer air to cause
strong vertical lift.
Tornado Wind Speed
As the tornado
moves along a
path, the circular
tornado winds
blowing opposite
the path of
movement will
have less speed.
Suction Vortices
A system of tornadoes
with smaller whirls, or
suction vortices,
contained within the
tornado is called a multivortex tornado.
Fujita Tornado Scale
Tornado watches are issued when tornadoes are likely,
while a warning is issued when a tornado has been spotted.
Once the storm is observed, or has passed, the Fujita scale
of F0 – F5 is used to classify tornadoes according to their
rotational speed based on damage done by the storm.
Tornado Breeding Supercell Storm
Supercell thunderstorms may have many of the
features illustrated here, including a mesocyclone of
rotating winds formed when horizontal vorticity was
tilted upwards.
Rotating Clouds
The first sign that a supercell may form a tornado
is the sight of rotating clouds at the base of the
storm, which may lower and form a wall cloud,
shown in this picture.
Non Supercell Tornadoes
If a pre-existing
wall cloud was
not present, than
any tornado
formed is not
from a supercell
storm, and is
often called a
funnel cloud, or
may be a
gustnado if the
form along a gust
front.
Waterspout Funnel
Warm, shallow coastal water
is often home to
waterspouts, which are
much smaller than an
average tornado, but similar
in shape and appearance.
The waterspout does not
draw water into its core, but
is a condensed cloud of
vapor.
Landspouts
Landspouts, which
form over land but
look like
waterspouts.
Doppler Radar Analysis
A single Doppler radar unit can
uncover many features of
thunderstorm rotation and
movement, but cannot detect winds
parallel to the antenna.
Dopplar lidar (light beam rather than
microwave beam) provides more
details on the storm features, and
will help measure wind speeds in
smaller tornadoes.
NEXRAD Wind Analysis
NEXt Generation
Weather RADar
(NEXRAD) is
operated by the
National Weather
Service and uses
Doppler measurement
to detect winds
moving toward
(green) and away
(blue) from the
antenna, which
indicates areas of
rotation and strong
shear.