SCIENCE NEWS
Severe Weather
characteristics of a
Severe Thunderstorm
Fueled by the increased instability of the
air
Intense
rotating updrafts as strong as
240km/h and lasting several hours
Know to produce: large hail, strong
surface winds, heavy rain and tornadoes
Severe thunderstorms
NationalWeather Service: - 3/4 inch
hail and/or 50 knot wind gusts at the
surface required to use term “severe”
Thebig difference from ordinary t-
storms is that many severe storms
have a tilted updraft this keeps the
downdraft from eventually killing the
storm
Severe thunderstorms
What is the name of a severe
thunderstorm that developed into
a self sustaining extreme storm?
SUPERCELLS
SUPERCELLS
Remember ????
A cell is formed in the Mature Stage
of a thunderstorm from the
up/downdraft
Ananvil shape of the
cumulonimbus cloud appears as the
updrafts hit the tropopause
SUPERCELLS
SUPERCELLS
SUPERCELLS & Strong
Winds
Winds speeds over 160k/hm
Violent
concentration of
downdrafts in a local area
known as downbursts
DOWNBURSTS
Classified by size of affected area
Macroburst: destruction up to 5 km
wide, wind exceeds 200 km/h, last
up to 30 min.
Microburst: destruction up to 3 km
wide, winds exceed 250 km/h, less
than 10 min
Macrobursts
Microbursts
SUPERCELLS & Hail
Hail
Collisionof super
cool water drops
forms layers
Formation from an
abundance of
strong up & down
drafts
SUPERCELLS &
Tornadoes
TORNADO
a violent whirling column
of air in contact with the
ground
Super cell that produced
a tornado
TORNADOES
Occurrence
Annually, the US has more than 1000
tornadoes 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.
TORNADOES
Features
Violent windstorm
Rotating column of air that extends down
from a cumulonimbus cloud
Low pressures inside causes the air to
rush into
Smaller suction vortices can form inside
stronger tornadoes
Rotating
clouds
are the
first sign
that a
super
cell may
form a
tornado
TORNADOES
Characteristics
Diameter between 500 & 2000 ft
Speed across landscape about 30 mph
Cut about a 6 miles long path
Most move toward the northeast
Intensity measured by the Fujita intensity
scale
Tornado Wind Speed
As the tornado moves
along a path, the
circular tornado winds
blowing opposite the
path of movement will
have less speed.
Example if the storm
rotational speed is 100
knots, and its path is 50
knots, it will have a
maximum wind of 150
knots on its forward
rotation side.
Tornados
Fujita Intensity Scale
Fujita-Damage Scale
Tornado damage
F5 Tornado damage
Tornado Damage
Other TORNADOES
Funnel Clouds
Rotating columns of air
Wind speed may exceed 200 knots
When the funnel cloud reaches the
ground it becomes a tornado
When the funnel cloud reaches the water
it becomes a waterspout
Waterspout
Dust-devil
ANY
QUESTIONS?
HOMEWORK
Read p 350 – 354