Transcript in southeast Colorado, and severe storms along a cold front from

Severe Weather
Conditions that form:
Thunderstorms
Tornadoes
Hurricanes
• http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es2002/es
2002page01.cfm?chapter_no=visualizatio
n
A. Thunderstorms
1. Created when:
a. cold dense air,
moving from the north
along the surface of
the earth, burrows
under a warm moist air
mass that is traveling
north.
b. The warm air rises
quickly producing
cumulonimbus clouds
Thunderstorm Stages
Stage 1: Cumulus
stage
Updraft
carries water vapor
to up in troposphere
where condensation
begins to form
cumulus cloud. The
cumulus clouds
expands both
vertically and
laterally..
Stage 2: Mature stage
The first drop of precipitation
reaches the ground.
Water droplets become too heavy for
the updraft.
Cloud tops exceed 60,000 feet
upwards.
Strong winds cause the cloud tops to
create an anvil shape. At the top of the
cloud ice crystals form.
Near the end of this stage, the rain
may be the heaviest, more lightning can
be created, and hail, strong winds and
tornadoes may form.
• Near the end of
this stage, the rain
may be the heaviest,
• more lightning can
be created,
• hail may be created
• strong winds and
tornadoes may form
Stage 3: Dissipating
Stage
The end of a
thunderstorm.
Precipitation falls
through the cloud,
breaks the cloud up.
During the
dissipating stage,
the humidity in the
air drops and the
precipitation ends.
Super cell thunderstorms
The stronger thunderstorms are called super
cells
Super cells are large, powerful
thunderstorms. These have strong vertical
wind with changes in wind speed and
direction.
Tornadoes can occur from these.
Human Impact
Lightning – power outages, personal
injury, deaths, fires, damage to
environment, property damage,
Floods- property damage, landslides,
deaths, emotional trauma, impedes
transportation,
Strong Winds – property damage, power
outages, possible deaths,
Hail – property damage, personal injury,
Rain/Snow – can create floods
B. Tornadoes
Created when:
•
during a
thunderstorm when
the warm air
spirals upward
(updraft)
•
latent heat is
released (as water
vapor
condenses).
• The rotating
updraft gains
velocity.
Tornados happen:
a. occur in the
spring and summer
b. most
frequent from
March to June
c. common in the
parts of Great
Plains, Texas and
Oklahoma =
Tornado Alley
Conditions for Tornado formation
a. Tornados form when strong cold, dry air
mass is overtaking a very warm, moist air
mass
b. Thunderstorms develop with strong
updrafts
c. The strong updrafts that are created
become a tornado.
Tornado Producing Storm along a
Cold Front
In the picture:
The satellite
showed a storm
system ("L") in
southeast
Colorado, and
severe storms
along a cold
front from
Kansas to Texas.
Picture and commentary from NOAA,gov
Dryline
• Where the
dry and the
moist air
meet is the
dryline.
• Updraft
occurs at this
point forming
storms and
possibly
tornados
As the tornado forms:
a. the storm
approaches, there is
a change in wind
direction and an
increase in wind
speed
b. This creates an
invisible, horizontal
spinning effect in the
lower atmosphere.
c. Rising air within the
thunderstorm
updraft tilts the
rotating air from
horizontal to
vertical.
d. An area of rotation,
2-6 miles wide, now
extends through
much of the storm.
Most strong and
violent tornadoes
form within this
area of strong
rotation
e. Moments later a
strong tornado can
develop in this area.
Supercell Tornado Formation
Tornadoes are
characterized by a
rotating updraft (usually
cyclonic)
This results from a
storm growing in an
environment of
significant vertical wind
shear.
Wind shear occurs when
the winds are changing
direction and increasing
with height.
Fujita Tornado Damage Scale
Developed in 1971 by T. Theodore Fujita
• F0 Wind speed < 73 mph
Light damage. Some damage to chimneys;
branches broken off trees; shallow-rooted
trees pushed over; sign boards damaged.
• F1 Wind speed 73-112 mph
Moderate damage. Peels surface off roofs;
mobile homes pushed off foundations or
overturned; moving autos blown off roads.
• F2 Wind speed 113-157 mph
Considerable damage. Roofs torn off
frame houses; mobile homes
demolished; boxcars overturned; large
trees snapped or uprooted; light-object
missiles generated; cars lifted off
ground.
• F3 Wind speed 158-206 mph
Severe damage. Roofs and some walls
torn off well-constructed houses; trains
overturned; most trees in forest
uprooted; heavy cars lifted off the
ground and thrown.
F4 Wind speed 207-260 mph
Devastating damage. Well-constructed
houses leveled; structures with weak
foundations blown away some distance; cars
thrown and large missiles generated
F5 Wind speed 261-318mph
Incredible damage. Strong frame houses
leveled off foundations and swept away;
automobile-sized missiles fly through the air
in excess of 100 meters (109 yds); trees
debarked; incredible phenomena will occur.
Why Tornadoes in the Spring and
Summer?
• Because the northern hemisphere is tilted
toward the sun, there is a greater
fluctuation between air mass temperatures
in the spring and the summer.
C. Hurricanes
1. Hurricane Overview
a. Definition: A hurricane is a large tropical
cyclone capable of high wind, heavy rains and
intense flooding
b. May include thunderstorms, tornados, winds
up to and beyond 155 MPH and storm surges of
15 feet or more
c. Storms turn counter-clockwise in the northern
hemisphere and clockwise in the southern
hemisphere
Rotation of a Hurricane
Cyclone Heta over The
South Pacific-Southern
Hemisphere – Jan 2004
•
•Notice the clockwise
rotation
• Hurricane Ivan over the
Gulf Coast – Sept 2004
• Notice the counterclockwise rotation.
2. Created when:
a. There is a pre-existing low pressure
disturbance
b. The ocean temp is at least 80o F.
c. There are light upper level wind-low
wind shear
Why Do Hurricanes Form in Summer?
Ocean Temperatures March 2003
Ocean Temperatures July 2003
Hurricanes
How Hurricanes form:
a. The low pressure disturbance
comes in contact with the warm
ocean water
b. As the warm, moist air rises, the
pressure decreases
c. As the air rises, it cools slightly,
condensing the water vapor.
d. This
condensation
releases heat
(latent heat)
adding more
energy to the
storm
More on Energy of a
Hurricane
e. The cloud tops will grow higher and the
storm will strengthen
f. As it gets stronger, the storm will start to
circulate around the low
4. Growth and death of a hurricane
a. If the storms stays over warm water and
upper level winds stay light, the storm will
usually strengthen
b. If the storms passes over cooler water,
the storm will start to dissipate
c. Landfall will quickly weaken a storm
because it shuts off it’s energy supply (heat)
d. The storm will re-intensify if it moves
over warmer waters again
Hurricane Ivan’s Path
5. Dangers of a hurricane
a. Storm Surge
1. Storm surge is a large dome of water 50 100 miles wide
2. Can be more than 15 feet deep
3. “Pulled up” by the decrease of air
pressure around the eye and “pushed
up” by the high winds
4. Greatest loss of life associated with storm
surges (flooding)
More Storm Surge
b. High Winds
1. The highest winds are generally on the
northeast (while making landfall on south
facing shores) or the north (while making
landfall on east facing shores).
2. They can rip apart roofs and destroy
unsecured buildings
3. Damage from flying debris as well
c. Rainfall
1. A typical hurricane can bring 6 to 12
inches of rain
2. This causes flash flooding and increasing
the flooding brought by storm surges
d. Tornados
1. Tornados can form on the fringes of the
storm
2. The greater the storm, the more tornados
are possible
Saffir - Simpson Scale
6. Saffir – Simpson Scale
a. Tropical Depression
Surface wind speeds below 39mph;
Must have formed over tropical
waters; Damage minimal; Not
named
Saffir - Simpson Scale
b. Tropical Storm
Surface wind speeds 40 mph – 73 mp:
Have some circulation; Damage to
foliage and unattached objects;
Named
Saffir – Simpson Scale
c. Category 1
Surface wind speeds 74
mph – 95 mph; No
real damage to
building structures
Damages mobile
homes, foliage and,
some coastal flooding
Hurricane Ophelia (2005)
Saffir – Simpson Scale
d. Category 2
Surface wind speeds 96
mph – 110 mph;
Roofing material and
windows damaged;
Piers damaged and
small watercraft can
break moorings
Hurricane Erin - 1995
Saffir – Simpson Scale
Aftermath of Hurricane Katrina:
Christian Pass MS, 2005
e. Category 3
Surface wind speeds
111 mph – 130 mph;
Major flooding along
coastal regions,
damage from floating
debris
Small buildings
severely damaged
Saffir – Simpson Scale
f. Category 4
Surface wind speeds 131 mph – 155 mph;
Roofs pulled off structures; Major beach
erosion; Major flooding damage of lower
floors of structures
Saffir – Simpson Scale: Cat. 4
Upper Left: Toppled House from NC
Lower Left: Damage from Dean, Jamaica 2007
Above: Hurricane Hugo 1989
Saffir – Simpson Scale
g. Category 5
Surface wind speeds greater than 155
mph.; Major damage to all buildings;
Small buildings completely gone; Most
building near shore completely damaged
or gone; Very few have made U.S. landfall
as a category 5
Saffir – Simpson Scale Cat. 5
Comparing Hurricanes Ophelia (Cat. 1) and Katrina (As a Cat. 5) 2005
Eye of Hurricane Katrina 2005
Damage from Hurricane Andrew, FL, 1992
Societal Impact of Hurricanes
7. Societal Impact of Hurricanes
a. Loss of Life
b. Property Damage
The Year That Was: 2005
• This was the first season on record with 26 named
storms in a single hurricane season. It was also the
first season that 7 tropical storms formed before
August 1st.
• A new record was set when 13 hurricanes formed in
the Atlantic Basin in 2005.
• Out of the 13 hurricanes that formed, 7 became major
hurricanes (category 3 or higher) and a new record
was set when three of those hurricanes (Katrina, Rita,
& Wilma) reached category 5 status in one season.
The Year That Was: 2005
• For the first time since records began, four
major hurricanes hit the U.S. (Dennis, Katrina,
Rita, Wilma).
• Five hurricanes (Dennis, Katrina, Ophelia, Rita
and Wilma) and three tropical storms (Arlene,
Cindy and Tammy) directly impacted the U.S.
• When this year’s list of hurricane names
expired, letters of the Greek alphabet were
used to name storms for the first time.
The Year That Was: 2005
• Hurricane Katrina is now the costliest hurricane on record with
at least $80 billion in damages. The previous record was
Hurricane Andrew (1992) with $26 billion in damages (1992
dollars) or $36 billion (2005 dollars).
• Hurricane Katrina was also the deadliest hurricane on record
since 1928 with at least 1,300 casualties.
• Hurricane Wilma became the strongest hurricane ever recorded
in the Atlantic Basin when the storm’s central pressure
plummeted to 882 mb. The previous record was in 1988 when
Hurricane Gilberts central pressure dropped to 888 mb.
Rotation of a Hurricane
• Cyclone Heta over The
South Pacific (Sothern
Hemisphere) – Jan 2004
•Notice the clockwise
rotation
• Hurricane Ivan over the Gulf
Coast – Sept 2004
• Notice the counterclockwise
rotation.
More on Energy of a
Hurricane