The Weather around Us
Weather = the state of the atmosphere at any given time
and place.
Extreme weather can
threaten lives, disrupt
transportation, and
cause billions of
dollars in destruction.
Billion dollar
weather
disasters,
1980-2005.
The Good Earth/Chapter 15: Weather Systems
The Atmosphere Checkpoint 14.2
When would oxygen have started to
accumulate in the atmosphere if the early
Earth had fewer land masses?
a) Before 2.5 billion years ago
b) After 2.5 billion years ago
c) 2.5 billion years ago (no change)
The Good Earth/Chapter 14: The Atmosphere
The Weather around Us
On average, 2-3 U.S. weather
disasters per year cause more than a
billion dollars in damage and threaten
numerous lives.
Today, more than 100 million
residents make the South the most
heavily populated region in the U.S.
People are migrating to Florida,
Georgia, and N.C. more than any
other state.
Most people are migrating from
states that have low incidences of
extreme weather events (New York,
Illinois, New Jersey).
Would you want to be riding in
one of these vehicles?
The Good Earth/Chapter 15: Weather Systems
The Weather around Us
• Almost 3 times as many people
die from extreme temperatures
than any other weather related
causes.
• More than 26,000 people in
Europe died in 2003 during
hottest summer on record
there (104°F or more).
• Extreme weather events can
change these statistics (e.g.
Katrina killed over 1,000
people)
• Extreme heat – “…underrated
and least understood of the
deadly weather phenomena.”
Weather-related fatalities.
The Good Earth/Chapter 15: Weather Systems
The Weather around Us
•
Can extreme heat, tornadoes, hurricanes, and other weather phenomena
be stopped?
− No, but meteorologists work to provide timely warnings.
− Hurricane Katrina – most expensive disaster in U.S. history.
− Over $100 billion in damage.
Hurricane
Katrina
approaches the
Louisiana coast,
August 28, 2005.
The Good Earth/Chapter 15: Weather Systems
Mid-latitude Cyclones
and Frontal Systems
A midlatitude cyclone
(a) At the point where a low-pressure
system (cyclone) interacts with
neighboring high-pressure systems, a
midlatitude cyclone forms. It is
centered over the low-pressure system
and is characterized by warm (red) and
cold (blue) fronts. Cloud cover
concentrates over the fronts and lowpressure center.
(b) Classic comma-shaped cloud pattern
associated with midlatitude cyclones.
Central U.S., Christmas Eve, 1997.
The Good Earth/Chapter 15: Weather Systems
Mid-latitude Cyclones and Frontal Systems
The boundary between
one air mass and another
is a front.
Frontal systems – pairs of
relatively narrow, long,
slightly curved regions
where air masses
interact.
Frontal systems bring
clouds and precipitation
and changes in moisture,
temperature, pressure,
and wind direction.
Weather patterns typically associated
with a cyclone (low-pressure system)
over the central U.S.
When warm and cold
fronts merge, they form
an occluded front.
The Good Earth/Chapter 15: Weather Systems
Mid-latitude Cyclones and Frontal Systems
Advancing Warm Fronts:
• Weather changes are not
as severe
- The warm air does not rise as
rapidly
-
Warm fronts slope gently
-
Warm fronts move more slowly
and the associated rain may last
longer than with a cold front
-
Warm fronts extend over a larger
area
-
Temperatures and humidity rise
-
Winds change direction
Occluded front. A cold air mass
overtakes a warm air mass.
Nimbostratus clouds generate
precipitation along an occluded
front.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Severe weather (as defined by NWS) has one or more of the
following elements:
A tornado
Damaging wind speeds (more than 58 mph)
Penny sized or larger hail
Only 10% of all the 100,000 thunderstorms that form over the
U.S. each year have these conditions.
Most thunderstorms are around 16 miles across and last less
than 30 minutes.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Moisture in the atmosphere + warm air + a lifting
mechanism = a thunderstorm!
The life cycle of a thunderstorm.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Lightening! Lightening joins two centers of opposite charge associated
with a thunderstorm. Cloud to ground lightening – negative charges in a
cloud are connected to positive charges on the ground. Cloud to cloud
lightening – opposite charges in one or more cloud are connected.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Thunderstorms can occur anywhere in the U.S. but their causes vary
by region:
Central or eastern portion of the states – isolated afternoon
thunderstorms in warm summer months when moist air rises. They
are typically brief and associated with a single large cloud called a cell.
Warm land surface heats the overlying air, causing it to rise, condense,
and generate a thunderstorm.
Eastern U.S. – thunderstorms associated with midlatitude cyclones.
Severe storms from a series of cumulonimbus clouds called
supercells. They are associated with frontal lifting along a cold front
between cP and mT air masses. Most common during spring and
early summer.
Rocky Mountains – related to orographic lifting.
Florida – warm maritime air rises due to several lifting mechanisms.
Thunderstorms are rare in Pacific coast states because weather is
influenced by cool ocean  more stable air.
The Good Earth/Chapter 15: Weather Systems
Weather Systems Checkpoint 15.14
Updrafts responsible for the formation of
thunderstorm clouds are most likely to
occur with which combination of
conditions?
a. Low-level warm, moist air; upper-level warm, moist air
b. Low-level cool, dry air; upper-level warm, moist air
c. Low-level warm, moist air; upper-level cool, dry air
d. Low-level cool, dry air; upper-level cool, dry air
The Good Earth/Chapter 15: Weather Systems
Weather Systems Checkpoint 15.16
Rank the three thunderstorm components
(air temperature, moisture, a lifting
mechanism) in order of their significance
in causing thunderstorms. Justify your
ranking.
The Good Earth/Chapter 15: Weather Systems
Weather Radar
Rain
Bow Echo
• Notice the big bow in this
squall line? It's called a
bow echo and the white
arrow is pointing to the
area that is likely going to
get very high winds. This
is an extreme case and if
you see this approaching
your location, very high
winds are likely.
Hook Echo
•
http://blogs.agu.org/wildwildscienc
e/category/radar/
Radar IN MOTION
Severe Weather: Thunderstorms and Tornadoes
Tornadoes = narrow, funnelshaped spirals of rapidly
converging and rotating air
that form in association with
thunderstorms.
Near-circular low-pressure
systems that rotate
counterclockwise in the
Northern Hemisphere
Pressure gradient is much
more intense for tornadoes
People have been “storm chasing” for about 50
years. Tourists pay companies to get them
into tornado prone areas to get footage of
tornadoes. Groups of tourists will pile out of
minivans and cheer as a tornado rips apart a
farmhouse. Is this sensible?
Tornadoes generate the
strongest natural winds on
Earth!
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
The worst tornado outbreak in U.S. history – April 3, 1974.
Tornadoes were spotted from Canadian border all the way
down to Gulf coast, and from Illinois to Virginia.
A total of 148 tornadoes touched down in 13 states.
330 people killed, over 5,000 injured.
A massive single tornado threw two tractor-trailers onto the
roof of a bowling alley in Xenia, OH as the storm sped
through at 50 mph.
33 people killed, 1300 buildings destroyed in Xenia that day.
http://www.weather.com/outlook/weathernews/news/articles/tornado-superoutbreak_2011-10-26
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Union City, OK
tornado May
1974.
a. Early stage
b. Mature stage
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Tornadoes are ranked on the Fujita intensity scale, which
places them in a category based on the destruction they
cause.
Rule of thumb: Weak tornadoes can tear shingles off the roof of
a house, strong tornadoes can tear the roof off a house, and
violent tornadoes can tear up the whole house.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Characteristics of tornadoes:
• Funnels are less than 2,000 feet wide
• Average funnel velocities are 31 mph, with highs of 125
mph
• Path of destruction typically 3-16 miles long
− Some may stay on ground for over an hour and
travel over 62 miles
Tornadoes follow the path of their parent thunderstorms (most travel east
or northeast, as they are often associated with midlatitude cyclone
thunderstorms.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
a. Early stage. Friction slows winds near surface. Higher wind velocity
moving upward from the surface. Contrasting vertical wind speed
generates counterclockwise winds about a central horizontal axis.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
b. Updraft stage. Updrafts below a thunderstorm draw spiraling horizontal
winds upward to form a mesocyclone within the larger storm cloud. These
are rotating thunderstorms that can be seen on radar (up to 6 miles across).
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
c. Tornado stage. Rotation in the mesocyclone forms small intense
spiraling winds within a newly formed tornado. These winds then extend
downward from a cloud base toward the ground surface.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Why do you
think U.S.
tornado
fatalities have
declined in the
past 50 or so
years?
Better
forecasting
and
warnings.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Thunderstorms and Tornadoes
Tornadoes occur
when
thunderstorm
activity is at an
optimum across
much of the
nation.
More common in
Gulf coast and
SE states in
early spring,
migrates to
Great Plains in
late spring.
Tornado Alley. The U.S. is home to the majority of
the world’s tornadoes, averaging about 1200 per
year. These states have an annual average of
more than 5 strong to violent tornadoes, 19501995.
The Good Earth/Chapter 15: Weather Systems
Weather Systems Checkpoint
15.20
Explain why the number of tornadoes
counted each year has increased, while
the number of days with at least one
tornado sighting has remained essentially
unchanged for several decades.
The Good Earth/Chapter 15: Weather Systems
Storm chasing break
Severe Weather: Hurricanes
Hurricane Katrina was the worst natural disaster to strike
the United States in the last century.
Are we doomed to repeat history? Can a hurricane strike
the same place twice?
More than 1,300 people died
An estimated $100 billion in damage in communities in Louisiana,
Mississippi, and Alabama
Much of the damage had long been predicted – A dozen major
hurricanes had made landfall along coastal Louisiana in the last century
Government reports, scientific articles, and newspaper stories had all
predicted what would happen if a major hurricane made landfall near
New Orleans
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Who should address the issue?
Scientists – best equipped to determine the probability and destruction
of a hurricane, but no funds or resources to do much about it.
Government – have power and funds for levees or evacuation plans, but
don’t always understand the seriousness of the threat.
“We learn from history that we learn nothing from history.” George
Bernard Shaw
Blue
areas =
flooded
areas
New Orleans before and after Katrina.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Key observations of
Katrina:
Large size
Dense mass of clouds
surrounding central clear
“eye”
Swirling spiral pattern of
clouds
Centered over the ocean
(Gulf of Mexico)
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Hurricanes originate in areas of the world’s oceans where the temperature
is greater than about 80°F. Hurricanes are most common in the summer
seasons of each hemisphere.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
How would you use these data if you worked for an insurance
company? How about a construction company?
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
What are hurricanes:
High winds
Heavy rainfall
Storm surges (elevated water levels) along coastlines
Not all hurricanes make land fall
Biloxi, Mississippi before and after Katrina.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
North Atlantic hurricane season  June 1 – November 30
Hurricanes only develop over warm (>80°F) water down to ~200 ft
Needs sufficient evaporation and condensation to foster large volume
of moisture to foster growth of huge cloud masses
Warm surface waters move north from equator in the summer in N.
Hemisphere creating optimal hurricane conditions
Development of Atlantic hurricanes that make landfall:
2-3 weeks prior to landfall – Cloud mass develops over warm ocean
water. Most storms generated in east Atlantic take about 3 weeks to
reach the coast of N. America
Katrina – developed in west Atlantic near the Bahamas.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Hurricanes begin to grow when warm, humid air is forced
aloft.
The rising air cools and condenses to form cumulus clouds
that will develop into cumulonimbus cells.
Earth’s rotation imparts a counterclockwise rotation to the
storm in the Northern Hemisphere. This rotation is zero at the
equator, therefore the majority of hurricanes originate between
10° and 20° N or S of the equator.
To maintain wind speed, inflow of air into developing lowpressure system must be matched by outflow of air in the
upper troposphere.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
1-2 weeks prior to landfall – Tropical depression develops (winds 2339 mph). After about 5 days this develops into a tropical storm
(winds 39-74 mph). Finally, a hurricane develops (winds at least 119
mph).
Air pressure is lowest in the eye, where warm air is
rising.
The lower the pressure inside the hurricane, the faster the
winds.
Hurricanes will continue to grow in size and intensity as
long as underlying water temperature remains above
80°F.
Precipitation concentrates within 124 miles on either side
of eye, releasing up to 20 billion tons of water per day.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
3-7 days before landfall – Atlantic hurricanes are
driven west by prevailing winds at 6-16 mph.
Florida and Texas experience more landfalls than any
other state.
Hurricane may turn parallel to the east coast or pass
south of Florida to strike the Gulf Coast or Caribbean
islands.
2-3 days before landfall – The likely landfall site is
identified.
Evacuations should be in full gear by now.
1-2 days before landfall – Size and slow motion of
hurricanes means their impact is drawn out over
several days.
Effects can reach coast before worst affects from the
eye.
Predicted landfall
site of Katrina. It
hit within 19 miles
of the predicted
site.
Measurements are made off coast by buoys to gather
info about eye
Waves over 100 feet high during Katrina
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Winds in the NE
quadrant blow
onshore, piling up
water in a storm
surge.
Surges cause ~90%
of the damage in
coastal areas.
Can potentially
reach inland areas
up to 6-12 miles
from shore.
Katrina – water
reached heights of
30 feet above sea
level in NE quadrant
of storm.
Winds in NW quadrant blow offshore. In the
case of Katrina, winds in NW quadrant pushed
water from Lake Pontchartrain (located NW of
the city) over levees into the city.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Hurricanes can take days to make their way
onshore.
Hurricanes lose intensity over land because of
frictional drag and loss of a moisture source.
Damaging winds near the core have speeds similar
to F1-F3 tornadoes.
Can rain up to 24 inches of rain in just a few days
over inland regions.
Water causes major erosion and damage from
flooding.
Erosion from hurricane Ivan
eroded most of N segment
of Chandeleur islands, LA.
In box – lighthouse.
The Good Earth/Chapter 15: Weather Systems
Severe Weather: Hurricanes
Katrina – category 3 hurricane
In 1973 in Bangladesh – Cyclone pushed onshore from Bay of
Bengal
22-foot storm surge produced widespread flooding on the low lying
plain
300,000 deaths
The Good Earth/Chapter 15: Weather Systems