Download ND-severe_weather

Severe Weather
Solar Heating and Latitude
Solar Heating and the Seasons
Relationship of sun angle and solar
radiation received on Earth
Solar Heating and Atmospheric
Circulation

Air at high elevations:



Cooler
Expands
Water vapor tends to
condense

Air at sea level:



Warmer
More compressed
Can hold more water
vapor
Air Circulation & Convection
Currents
Coriolis Force
Atmospheric Circulation &
Convection Cells
Air masses are classified on the
basis of their source region
Fronts
 Types

of fronts
Warm front
•
•
•
•
•
•
Warm air replaces cooler air
Shown on a map by a line with semicircles
Small slope (1:200)
Clouds become lower as the front nears
Slow rate of advance
Light-to-moderate precipitation
Fronts
 Types

of fronts
Cold front
•
•
•
•
•
Cold air replaces warm air
Shown on a map by a line with triangles
Twice as steep (1:100) as warm fronts
Advances faster than a warm front
Associated weather is more violent than a warm
front
Cold Fronts and Warm Fronts
Rotating Air Bodies
 Bends
in the polar jet create troughs and
ridges
 Forms cyclones and anticyclones
Rotating Air Bodies

Low Pressure Zone
Formation



Warm air rises
Creates a low
pressure zone
At the Earth’s surface,
air “feeds” the low
pressure zone, moves
counterclockwise

High Pressure Zone
Formation



Cool air sinks
Creates a high
pressure zone
At the Earth’s surface,
winds blow clockwise
Cyclones and Anticyclones
Types of Severe Weather
 Thunderstorms
 Snow
/ Rain storms
 Mid-latitude cyclones


Blizzards
Tornadoes
 Tropical



cyclones
Typhoons in the western Pacific
Cyclones in the Indian Ocean
Hurricanes in the U.S.
Stages in the development
of a thunderstorm
Thunderstorms
 How
Lightning Works
Thunderstorms
Lightning Varieties
cloud-to-ground
Blue jets
Cloud discharge
Red sprites
Ball lightning
Elves
(NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)
Lightning Varieties
Volcanic Lightning
Nuclear Lightning
Triggered Lightning
(NOVA: Science Now – Lightning http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html)
Thunderstorms
 Lightning


- Don’t Get Struck!
Boating or swimming – get away from the
water.
Try to take shelter in:
• substantial, permanent, enclosed structures.
• a car, truck or other hard-topped vehicle.
• an area protected by a low clump of trees.

No shelter available?
• Find a low-lying, open place away from trees,
poles/metal objects and water.
• Make yourself the smallest target possible.
• Do not lie flat, as this makes you a larger target.
Severe weather types
 Tornadoes

How a Tornado Forms
• Moist air from Gulf of
Mexico
• Fast moving cold, dry
air mass from Canada
• Jet stream moving east
at 150 mph
• Sets up shearing
conditions
Severe weather types
 Tornadoes

How a Tornado Forms
• Warm moist Gulf air
releases latent heat,
creates strong updraft
• Updraft sheared by
polar air, then twisted in
a different direction by
jet stream
Severe weather types
 Tornadoes


Why do some thunderstorms spawn
tornadoes while others do not?
Super Cell Thunderstorms
Severe weather types
 Tornadoes

The Fujita-Pearson Scale
• The size of a
tornado is not
necessarily an
indication of its
intensity!
Tornadoes
 “Tornado

Capitol of the World”
CNN’s “10 deadliest U.S. tornadoes”
Source: cnn.com
Tornadoes
 Tri-State

Tornado, 18 March 1925
Largest tornado known
• Travelled 353 km (219 mi)
across Missouri, Illinois
and Indiana
• Widest swath recorded
- 1 mi in diameter


In this photo, engineers examine a board
that the tornado's high-speed winds drove
through a larger plank. cnn.com
Devastated 23 cities
Killed 695 people and injured 2,027
Tornadoes
 The




Super Outbreak, 3-4 April 1974
5 weather systems collided
Dry air from the SW overrode moist Gulf air,
creating an inversion layer
Gulf air pushed through the inversion layer
Thunderstorms developed
Tornadoes
 The
Super Outbreak,
3-4 April 1974

147 tornadoes
• 6 F5 tornadoes


13 states
16 hours
Tornadoes
 Why



don’t tornadoes strike large cities?
Occur over large regions
Cities are relatively small targets
Oklahoma City Tornado (1999)
Tornadoes
 Safe


Rooms
Best ones are underground
Some are above ground
Mid-latitude Cyclones
 Idealized

weather
Middle-latitude cyclones move eastward
across the United States
• First signs of their approach are in the western sky
• Require two to four days to pass over a region

Largest weather contrasts occur in the spring
Mid-latitude Cyclones
Mid-latitude Cyclones
 Nor’easters

The Eastern U.S. “White Hurricane” of 1993
• AKA “Storm of the Century”
• Three storm fronts all converged with a trough in
the jet stream
• Collision began in Florida, and moved up the
eastern seaboard with the jet stream
• 238 people died from Cuba to Canada
• 48 sailors lost at sea
2
3
1. Low pressure zone
from Gulf of Mexico –
lots of thunderstorms
2. Trough in jet stream drew
in fast-moving arctic front
1
X
3. Trough also drew in a
rain/snow front from the
Pacific
Mid-latitude Cyclones
 Blizzards

Form when a long cyclone brings
• Cold 60 km/hr winds
• Freezing temperatures
• Lots of snow


Can travel very slowly
Storm itself usually doesn’t kill
• Shoveling snow, auto accidents, etc.
Mid-latitude Cyclones
 Blizzards

Northeastern United States, 6-8 January 1996
• Storm centered on Ohio, Pennsylvania, West
Virginia, and New Jersey
• 50 mph winds, record snow falls
• 154 people died
• Warm, wet weather immediately followed
• 187 people died
Mid-latitude Cyclones
 Ice

Storms
Formation:
• Falling snow and ice melt, change to rain, then
freeze again as they reach the ground
• Sleet
• Freezing rain
Mid-latitude Cyclones
 Ice

Storms
Canadian Ice Storm, 5-9 January 1998
• 80 hours of freezing rain
• Power systems collapsed



had to be completely replaced
People without power for up
to 4 weeks
16 U.S. and 28 Canadian
deaths
• Damages


$1.4 billion for the U.S.
$3 billion for Canada
Source: cnn.com
Hurricanes
Hurricanes
 Only
natural disaster that is given a human
name
 Actually large tropical cyclones
 Convert heat in the ocean into winds
 Exports excess heat from the tropics to the
midlatitudes
Hurricanes
 How

a Hurricane Works
Tropical disturbance
• Low pressure zone develops and draws in clusters
of thunderstorms and winds
Hurricanes
 How


a Hurricane Works
Tropical disturbance
Tropical depression
• Surface winds strengthen, move about the center
of the storm
• Central core funnels warm moist air up towards
stratosphere
• Air cools, vapor condenses, latent heat released
• Fuels more updrafts, cycle repeats, storm grows
Hurricanes
 How



a Hurricane Works
Tropical disturbance
Tropical depression
Tropical Storm
• Storm has sustained surface wind speeds of +39
mph
Hurricanes
 How




a Hurricane Works
Tropical disturbance
Tropical depression
Tropical Storm
Hurricane
• Surface winds consistently over 74 mph
Hurricanes
 How





a Hurricane Works
Tropical disturbance
Tropical depression
Tropical Storm
Hurricane
The Eye
• As wind speed increases, winds are spiraled
upwards prior to reaching the center
• A distinctive clear “eye” is formed
• Strongest winds are located on the walls of the eye
Hurricane Wind Patterns
Hurricane Origins
in the tropics ~ 5° and 20 ° latitude
 Cannot form at the equator
(Coriolis effect = 0)
 Form
Hurricanes
 Hurricane

Damages
Storm Surges
• Large mound of water builds up beneath the eye
• Reaches land as a surge of water
Hurricanes
 Hurricane

Damages
Storm Surges
• Wind speed varies
depending upon which
side of the hurricane
you’re on
• Amount of damage on the
coastline will vary
accordingly
Hurricanes
 Hurricane



Damages
Heavy Rains
Mudflows and Debris Avalanches
Flooding
Hurricanes
 Hurricane


paths
Curves due to
Coriolis affect
Storms must go
around high
• Strong and large –
storms to Atlantic
seaboard
• Small and to the
north – storms may
miss the U.S.
Hurricane Paths
Forecasting the Hurricane
Season
 Frequency
of hurricanes in the North
Atlantic is affected by climate



Wet Sahel region in Africa = more
thunderstorms
Warm SST = more energy for tropical
depressions
Low atmospheric pressure in Caribbean =
more cyclones
Forecasting the Hurricane
Season
 The


La Nina / El Nino Connection
La Nina present in Pacific = more winds to
move storms
El Nino present in the Pacific = less winds,
disrupts storms
Cape Verde-type Hurricanes





Begin as low pressure storms in western Africa
Travel west within the trade wind belt
Strengthen as they reach subtropical waters
Trade winds move cyclone westward
Coriolis affect moves the storms northward
How Hurricanes Form (source: AP.org)
Cape Verde-type Hurricanes
 Hurricane

Katrina in Florida
Thursday, Aug. 25, 2005
• Category 1 hurricane
• Crossed the southern tip of Florida then headed
into the Gulf of Mexico.
AP’s Hurricane Tracker (flash file) | AP’s Katrina’s Impact (flash file)
Cape Verde-type Hurricanes
 Katrina

in Florida
Facts:
•
•
•
•
Eleven Deaths
Evacuations ordered
Numerous power outages
Damages est. from $600 million to $2 billion.
Katrina in Florida
 Storm
waves
Russell Crossey and his dog get a serious
soaking Thursday on the north jetty of the
Boynton Inlet in Manalapan, Florida, as
huge waves, whipped up by Katrina, break
against the wall. (cnn.com)
Keena Baker took this photo of waves hitting
the Dan Russell Municipal Pier in Panama City
Beach. The pier is still damaged from Hurricane
Dennis that hit Florida in July. (cnn.com)
Katrina in Florida
 Flooding
This south Miami Heights neighborhood is
sinking in floods after a visit from Hurricane
Katrina. (cnn.com)
South Miami-Dade County as seen during a fire
department aerial reconnaissance mission in the
wake of Hurricane Katrina on August 26, 2005.
Photograph courtesy Lt. Eric Baum/Miami-Dade
Fire Rescue (nationalgeographic.com)
August 29: Louisiana
Category 4
August 25-26: Florida
Category 1
Katrina in the Gulf States
cbsnews.com
Cape Verde-type Hurricanes
(Mario Tama/Getty Images)
 Katrina

in the Gulf States
Emergency Shelter
• Not everyone could
evacuate
• 10,000+ people took shelter
in the Louisiana Superdome
(cnn.com)
(cnn.com)
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
Storm Surge
• 20+ feet (6 m) at Louisiana / Mississippi border
• 10 feet (3 m) at Mobile Bay, Alabama
A casino barge sits among homes in
Biloxi (Photo: AP) (cbsnews.com)
The storm surge from Hurricane Katrina
floods a parking lot in downtown Mobile,
Ala. (AP Photo/Michelle Rolls, Mobile Register)
Cape Verde-type Hurricanes
 Katrina
in the Gulf States
The I-90 bridge over St. Louis
Bay is the end of the road
after the high winds and
waves of Hurricane Katrina
hit the area destroying the
bridge.(AFP/Paul J. Richards)
A boat sits among trailers
damaged by Hurricane
Katrina Wednesday, Aug. 31,
2005, in Gulfport, Miss. (AP
Photo/David J. Phillip)
A casino barge damaged by
Hurricane Katrina sits on the
road Wednesday, Aug. 31,
2005, in Gulfport, Miss. (AP
Photo/David J. Phillip)
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
High Winds
Debris from the storm in Mississippi.
(Mississippi Press-Register, William
Colgin/AP Photo) (abcnews.com)
Trees litter New Orleans streets after
Hurricane Katrina pounded the city
on Aug. 29, 2005. (Dave Martin/AP
Photo) (abcnews.com)
Katrina in the Gulf States
cbsnews.com
Katrina in the Gulf States
cnn.com
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
Urban Flooding
The Mound Underpass on Interstate 10 is flooded near
downtown New Orleans on Monday. (cnn.com)
Floodwaters from Hurricane Katrina fill the
streets near downtown New Orleans Tuesday,
Aug. 30, 2005 in New Orleans.
(AP Photo/David J. Phillip)
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
Urban Flooding
Oil slick in water surrounding a house in
New Orleans (AFP/Pool/Vincent Laforet)
A toxic film spreads over the water near a
flooded home in a lakeside area in New
Orleans, Louisiana. (AFP/Getty
Images/Dave Einsel)
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
Urban Flooding / Levee
Failure
REUTERS/Marc Serota
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
Structural Damage
A toppled brick wall in the French Quarter.
Photograph by Mario Tama/Getty Images
(nationalgeographic.com
An old building near the French Quarter in New
Orleans is severely damaged by the storm
Monday. (cnn.com)
Cape Verde-type Hurricanes
 Katrina

in the Gulf States
Indirect effects









Lack of electricity / power
Lack of telecommunications
Lack of clean water
Lack of food / water / clothing / medicine
Lack of health care
Lack of employment
Shelter compromised
Access to personal funds compromised
Increased “critter” activity (snakes, alligators)
Caribbean Sea and Gulf of
Mexico-type Hurricanes
 Form
in the Intertropical Convergence
Zone (ITCZ) – Caribbean Sea & Gulf of
Mexico
 SW blowing Trade Winds of the N
Hemisphere collide with the NW blowing
Trade Winds of the S Hemisphere
 ITCZ moves with the tilt of the Earth’s axis
Caribbean Sea and Gulf of
Mexico-type Hurricanes
Caribbean Sea and Gulf of
Mexico-type Hurricanes
 Mitch,



October 1998
Formed in the Caribbean
Sea
Within 36 hours it was a
hurricane
Stalled off the Honduras
& Nicaragua coast
• 25-75” of rain fell over three days
Caribbean Sea and Gulf of
Mexico-type Hurricanes
 Mitch,

October 1998
Nicaragua:
• 3800 people killed
• 2000 killed when a
crater lake
overflowed and
created a lahar

15 day total:

Honduras:
• 6500 people killed
• 20% of population
left homeless
• 60% of roads
unusable
• 70% of crops
destroyed
• 11,000 people died
• Second deadliest hurricane on record
Hurricanes and the Gulf of
Mexico Coastline
 Gulf
of Mexico Coast
Example: Texas



Passive coastline
Lots of barrier islands
and broad, flat
beaches
Low in elevation
Hurricanes and the Gulf of
Mexico Coastline
 Galveston,







Texas, September 1900
Built on a low-lying sand island
38,000 residents in 1900
Hurricane warning issued, many evacuated
Hurricane hit the island in the afternoon
Covered the entire island with water
6000 people died
Half the houses destroyed, in addition to all
forms of communication
Hurricanes and the Atlantic
Coastline
 The



Evacuation Dilemma
Population growth exceeds building of new
roads
Need to evacuate several days in advance
No guarantee that the hurricane will strike the
area evacuated
Oblique aerial photographs taken on Topsail Island, North Carolina before and after Hurricane
Fran in 1996. The yellow arrows point out the same buildings in both photos. Note the destroyed
buildings, the overwash, and the damaged road in the post-storm photo on the right.
Reduction of Hurricane
Damages
 Building

Codes
Roofs
• Make it either easier or harder for roof to lift off
• Strap roof to walls
• Ban use of staples to secure roofing materials
Reduction of Hurricane
Damages
 Building

Codes
Impact of Wind-borne Debris
• Protect windows
• Pick up around the house
• Landscape with native species
Reduction of Hurricane
Damages
 Land-Use
Planning
 Coastal Development Restrictions
Global Rise in Sea Level
 Average
rise 1 foot per
century
 Response is to build
seawalls

Cause more harm than
good
Hurricanes and the Pacific
Coastline
 Pauline,
October 1997
 Iniki, September 1992
Cyclones and Bangladesh
Cyclones and Bangladesh
Cyclones and The Bay of
Bengal
 Bangladesh

Has one of the worst
records for natural
disasters






Floods
Cyclones
Tidal surges
Tornadoes
Droughts
and even cold spells.
Cyclones and The Bay of
Bengal
 Bangladesh

1971
• Over 1,000,000 people dead
• country's entire infrastructure on the south coast
was wiped out.

1991
• Cyclone killed nearly 140,000 people, most of
them women and children.
• Government cyclone shelter program
Cyclones and The Bay of
Bengal
 The


Indian “Super Cyclone” 1999
Hit the Indian state of Orissa hardest
Indian officials state that
“development in the state
has been set back an entire
generation”
Cyclones and The Bay of
Bengal
 The

Indian “Super Cyclone” 1999
Orissa is one of India’s poorest states
•
•
•
•
•
India's highest infant mortality rate
2/3 of the rural population living in abject poverty
lowest number of doctors per capita
Lack of electricity and water
< 5% of the population has access to subsidies for
food and fuel aimed at poverty-alleviation.
Cyclones and The Bay of
Bengal
 The

Indian “Super Cyclone” 1999
Most of the damage caused by
 Storm surge
 Heavy rainfall
 Flooding
Oct 29
Landfall
Oct 27
Hurricane
Oct 26
Tropical
Storm
Nov 01
Tropical
Disturbance
Oct 24
Disturbance
forms
Cyclones and The Bay of
Bengal
An aerial view of the heavily-damaged
Paradip port, where the cyclone made landfall.
Large areas of Orissa are still under water &
entire villages are feared to be submerged.
Cyclones and The Bay of
Bengal
 The

Indian “Super Cyclone” 1999
The Human Cost
• As of 10th November 1999 the death toll was
estimated at 7,500, but expected to rise to near
10,000.
• Over ten million were affected by the cyclone of
which at least a million have been made homeless.
~ End ~