Transcript Weather - dawson78ips

WEATHER SYSTEMS
Quick Review
• What causes wind?
Answer: uneven heating of the earth by the sun.
• Is hot air high pressure or low pressure?
Answer: low pressure.
• What about cold air?
Answer: high pressure
• Which type of air rises? Which one sinks?
Answer: hot air (low pressure) rises, and cold air (high pressure) sinks.
Now lets talk about Air Masses
Air Masses
A large body of air that has nearly the same temperature and humidity
throughout- They have similar properties as the part of the earth’s surface
over which they form.
Why are Air Masses important?
• They can cover an area of thousands of
square kilometers.
• They are responsible for day to day
weather changes.
Which way do the winds blow?
high
low
• From ___________
pressure to _____
pressure.
Do you know what instrument we use to measure air pressure?
A Barometer
Cyclones
• In the northern hemisphere, once wind
blows into a low pressure area, it rises in a
counterclockwise direction; this is called a
cyclone. Low pressure areas usually have
stormy weather. ** This is not the
same as a tornado**
Anticyclones
• Wind also blows AWAY from the center
of high pressure. In the northern
hemisphere, this wind blows in a clockwise
direction. High pressure areas usually
have good weather.
Fronts
• What is a front?
• It is a boundary between two air masses of
•
different density, moisture, or temperature.
There are four types of fronts; can you name
Cold front
Warm front
them?? _____________,
______________
Occluded front
Stationary front
_____________,
and ______________
Precipitation Along a Cold Front
lifting the warm moist air ahead of it
A Closer Examination of the Animation:
Initially, the cold air mass wedges into the warmer air mass ahead
of it, (separated from each other by the cold front). The lighter
warm air is lifted upwards by the denser cold air and if enough
water vapor condenses, clouds develop.
Precipitation Along a Warm Front
warm moist air overriding colder air
A Closer Examination of the Animation:
Initially, a warm air mass (in yellow) nudges against a colder air
mass (in blue) ahead of it, (separated from each other by the
warm front). The lighter warm moist air behind the front is lifted
upward and "overrides" the colder air.
Stationary Front
SEVERE WEATHER
What is a thunderstorm?
- A thunderstorm is a weather event where there is heavy rain,
lightning, thunder roars, and possible hail.
How do they form?
-They occur in warm moist air masses and along fronts.
cooled
-The air is forced upward where it is __________,
and
cumulonimbus
condensation occurs forming _________________clouds.
precipitation
-Then __________________
happens in the form of rain or
hail. The rain cooled air sinks and strong updrafts of warmer
air causes strong winds.
Can thunderstorms cause damage?
• YES!
• How?
• By flooding
• Hail damage
• Wind damage
• Lightning strikes
What is lightning?
Lightning is a bright flash of electricity produced by a
thunderstorm. All thunderstorms produce lightning and are
very dangerous. If you hear the sound of thunder, then you
are in danger from lightning. Lightning kills and injures more
people each year than hurricanes or tornadoes; between 75 to
100 people.
What causes lightning?
Lightning is an electric current. In a thundercloud, many small bits of ice
(frozen raindrops) bump into each other as they move around in the air. All
the collisions create an electric charge. Once the cloud fills, with electrical
charges, the positive charges form at the top of the cloud and the negative
charges form at the bottom of the cloud. Since opposites attract, this
causes a positive charge to build up on the ground beneath the cloud. The
grounds electrical charge concentrates around anything that sticks up,
such as mountains, people, or single trees. The charge coming up from
these points eventually connects with a charge reaching down from the
clouds and - zap - lightning strikes!
Lightning
can
alsoforms
form within
between
clouds,
not just
Lightning
also
withinorand
between
clouds.
from the cloud to the ground
What causes thunder ?
Thunder is caused by lightning. When a lightning bolt travels
from the cloud to the ground it actually opens up a little hole
in the air, called a channel. The lightning heats up the air and
causes it to expand. Once the lightning is gone the air
collapses back due to quick cooling, and creates a sound wave
that we hear as thunder. The reason we see lightning before
we hear thunder is because light travels faster than sound!
Which do you think is hotter, a bolt of lightning, or
the surface of the sun?
Lightning- it is 30,000 degrees
Celsius. That’s 5 times hotter
than the sun!!
Can you tell how far away a thunderstorm is?
Yes, you can use thunder to tell how far away a storm is. Next
time you see a storm, count the number of seconds between
when you see the lightning and hear the thunder. Take the
number of seconds and divide by 5 and that will tell you how
far away the storm is in miles. For example: If you counted 10
seconds between the lightning and the thunder, the lightning
is 2 miles away!
How do tornadoes form?
When thunderstorms develop, a change in wind direction and
an increase in wind speed with increasing height creates an
invisible, horizontal spinning effect in the lower atmosphere;
this is wind shear. Rising air from the updraft of a
thunderstorm tilts the rotating air from horizontal to vertical.
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.
Know the Lingo
TORNADO WATCH - Tornadoes are possible in your area. Stay tuned to the radio or
television news.
TORNADO WARNING - A tornado is either on the ground or has been detected by Doppler
radar. Seek shelter immediately!
Measuring Tornadoes
The Fujita Scale
F0
gale tornado
40-72 mph
F1
moderate tornado
73-112 mph
F2
significant tornado
113-157 mph
F3
severe tornado
158-206 mph
F4
devastating tornado
207-260 mph
F5
incredible tornado
261-318 mph
Some damage to chimneys; breaks branches off trees; pushes over shallowrooted trees; damages sign boards.
Lower limit is the beginning of hurricane-force winds. Peels surface off roofs;
mobile homes pushed over; moving autos pushed off roads.
Roofs torn off frame houses; mobile homes demolished; boxcars pushed over,
large trees snapped or uprooted; light-object missiles generated.
Severe damage. Roofs and some walls torn off well-constructed homes; trains
overturned; most trees in forest uprooted; heavy cars lifted off the ground and
thrown.
Well-constructed homes leveled; structures with weak foundations blown off
some distance; cars thrown and large missiles generated.
Phenomenal damage. Strong frame homes disintegrate or lifted off
foundations and carried considerable distance; trees debarked.
Where are tornadoes most likely to occur?
The geography of the central part of the United States,
known as the Great Plains, is suited to bring all of the
ingredients together to forms tornadoes. This includes Texas,
Kansas, and Oklahoma. More than 500 tornadoes typically
occur in this area every year and is why it is commonly known
as "Tornado Alley".
What is a hurricane?
A hurricane is a huge storm! It can be up to 600 miles
across and have strong winds spiraling inward and
upward at speeds of 75 to 200 mph. Hurricanes usually
lasts for over a week, moving 10-20 mph over the open
ocean. Hurricanes gather heat and energy through
contact with warm ocean waters. Evaporation from the
seawater increases their power. Hurricanes rotate in a
counter-clockwise direction around an "eye." The center
of the storm or "eye" is the calmest part. It has only light
winds and fair weather. When they come onto land, the
heavy rain, strong winds and large waves can damage
buildings, trees and cars. Similar storms are called
typhoons in the Pacific Ocean and cyclones in the Indian
Ocean.
How do hurricanes form?
Hurricanes form over warm ocean water of 80°F or warmer.
The atmosphere must cool off very quickly the higher you go.
The wind must be blowing in the same direction and at the
same speed to force air upward from the ocean surface.
Winds flow outward above the storm allowing the air below
to rise. Hurricanes typically form between 5 to 15 degrees
latitude north and south of the equator. The Coriolis effect
is needed to create the spin in the hurricane.
Saffir-Simpson Hurricane Scale
Category
Winds (MPH)
Storm Surge
(Feet)
1
74-95
4'-5'
2
96-110
6'-8'
3
111-130
9'-12'
4
131-155
13'-18'
Extensive
Extreme
5
>155
>18'
Catastrophic
Damage
Minimal
Moderate
Can Hurricanes cause damage?
• Absolutely!
• Storm surges usually cause the most
damage and death
• Winds can destroy homes and uproot
trees
• Extensive rain can also cause major
flooding
What is a storm surge?
Shallow-Water Coastline
Deep-Water Coastline
Know the Lingo
TROPICAL STORM WATCH - Tropical Storm conditions with sustained
winds from 39 -74 mph are possible in your area within the next 36
hours.
TROPICAL STORM WARNING - Tropical Storm conditions are
expected in your area within the next 24 hours.
HURRICANE WATCH - Hurricane conditions with sustained winds of
74 mph or greater are possible in your area within the next 36 hours.
This WATCH should trigger your family's disaster plan, and protective
measures should be initiated. Especially, those actions that require
extra time such as securing a boat and leaving a barrier island.
HURRICANE WARNING - Hurricane conditions are expected in your
area within 24 hours. Once this WARNING has been issued, your family
should be in the process of completing protective actions and deciding
the safest location to be during the storm
How do blizzards form?
A blizzard is a long-lasting snowstorm with
very strong winds and intense snowfall. You
need three things to have a blizzard; cold air
at the surface, lots of moisture, and lift.
Warm air must rise over cold air. Blizzards
have winds of at least 56 km/h, temperature is
below 20 degrees fahrenheit, and visibility is
less than 400 meters
Forecasting Weather
• What information do you need to know to
forecast weather??
• Temperature
• Winds
• Air pressure
• Humidity
• Precipitation
Do you know the scientific name
for a weather forecaster?
A Meteorologist is what they’re
called.
• Meteorologists measure temperature, air
•
•
pressure, winds, humidity, and precipitation.
They use Doppler radar, satellites, and
instruments attached to balloons to get their
information.
They gather information from the upper
atmosphere, as well as from the earth’s surface.
STATION MODEL
Key to Features
1 -- Cold Front
2 -- Warm Front
3 -- Stationary Front
4 -- Occluded Front
5 -- Trough ("TROF")
Also used to depict Outflow Boundary ("OUTFLOW BNDRY")
6 -- Squall Line
7 -- Dry Line
8 -- Tropical Wave ("TRPCL WAVE")
A hash mark denotes a change in frontal type, as in the example below.
Note: The hash mark will always be drawn perpendicular to the boundaries.
They are not drawn at "triple points" (the intersection of an occluded, cold and
warm or stationary front) and where a low pressure center separates the different
frontal types
A weather map showing surface-pressure systems, air masses, fronts, and
isobars (in millibars) as solid gray lines. Large arrows in color show air
flow. (Green-shaded area represents precipitation.) Isotherms are similar
to isobars, except they show temperature (Not Shown here)