Download Weather

Created by Mrs. Susan Dennison
2015-2015
The atmosphere is a layer of invisible
gas (air) that surrounds the Earth. It
wraps around the planet like a blanket.
All weather happens in
the lower atmosphere.
What causes weather?
Winds keep our atmosphere in motion (moving). Air moves in masses. Winds push
those masses around. All weather gets its start in the atmosphere. We can often
predict the movement of those air masses and therefore know what weather may
come our way. Scientists who study the weather are called meteorologists.
How is weather different from climate?
Weather: what conditions of the atmosphere are over a short period
of time
Climate: how the atmosphere "behaves" over relatively long periods
of time
A meteorologist is a scientist who collects
data about the weather and uses it to
make predictions, or forecasts.
People who study meteorology
depend on special instruments to help
them understand what has happened
and to forecast what will happen.
A thermometer is the device that
measures the temperature (amount of
thermal, or heat energy) of the air and
tells us how hot or cold it is in degrees.
17° C
62° F
Degrees in Fahrenheit
Degrees in Celsius
*Most of Europe and the rest of
the world use this system.
*This is a system we most
commonly see in the U.S.
The two scales used to measure
temperature are named after their
inventors who lived in the early 1700s.
Fahrenheit
Celsius
Fresh water freezes at 32° F
Fresh water freezes at 0°C
Human body is 98.6° F
Human body is 37° C
Water boils at 212° F
Water boils at 100° C
Anemometers are instruments that
measure wind speed and sometimes direction.
Wind or weather vanes are instruments that
tell from which direction (n,s,e,w) the wind is blowing.
Barometers are instruments that
measure air pressure– the weight
of the atmosphere.
The dial has numbers and sometimes pictures of a cloud or sunshine.
The HIGHER the air pressure, the drier the weather is likely to be.
The LOWER the air pressure, the nastier the weather is likely to be.
Air pressure is the force caused by the weight of the
air pushing on things. The wind blows from areas of
high pressure (high means “heavier”) towards areas
of low pressure (“less pressure”). Warm air rises and
cool air sinks towards the ground.
HIGH PRESSURE = happy weather
LOW PRESSURE= less happy weather
Rain gauges are instruments that
measure the amount of rain that has
fallen. Rain falls into a large cylinder that
has measurement markings on the side.
Hygrometers are instruments that
measure the amount of humidity, or
moisture, there is in the air. When it is
humid, we usually feel sticky and our hair
gets frizzy. If it is hot, we feel “icky.”
*Higher numbers show more moisture.
The air is more “wet.”
Satellites are machines that scientists also use to keep an eye
on our weather. They hover over our Earth and send
information and pictures back to groups like The National
Oceanic and Atmospheric Administration (NOAA).
Where do clouds come from?
1. Water evaporates.
2. The air becomes full of water vapor (clouds are condensing water vapor).
3. Air currents rise.
4. Water vapor condenses and falls as water droplets or
frozen precipitation (rain, sleet, snow, hail).
Clouds are made of billions of tiny
droplets of water formed around specks of
dust in the air. Fog is a cloud close to the
ground. There are many types of clouds.
Cirrus clouds are “feathery” and usually
are seen on fair (good) weather days.
Cumulus clouds are fluffy,
white clouds with flat bottoms. The
billow out, change shape, and even look
like familiar shapes or cotton balls. The
usually indicate fair (good) weather.
Stratus clouds are smooth and gray. They
cover the whole sky, like a gray blanket,
and block direct sunlight. They usually
indicate light rain, drizzle, or snow (if it is
cold enough).
Cumulonimbus clouds are big, “stacked,” and
darker on the bottom. ‘Cumulo-nimbus’ is
Latin for “heap rain.” They usually indicate
downpours of rain, hail, lightning, high winds,
and sometimes even tornadoes!
Precipitation: hail, rain, sleet, and snow
In Virginia, we are most likely to see hail
and rain during the summer. It does not
have to be cold outside for us to see hail!
Precipitation: hail, rain, sleet, and snow
When rain and snow are mixed, we
experience sleet, which is “slushy.” We see
this when temperatures are just slightly above
freezing and rain or snow is in the forecast.
Precipitation: hail, rain, sleet, and snow
If both the air temperature in the clouds and
the atmosphere is below freezing, we will
experience snow, or frozen precipitation.
Dew forms when warm, moist air cools
down causing water to condense. Ever
notice dewy grass on a foggy morning?
If there is a lot of water vapor in the air,
meteorologists tell us that it is very
humid outside. When there is a lot of
humidity, many of us feel “icky and
sticky,” especially if it is also hot outside!
What else can tell a meteorologist that
wild weather is in our future? Areas where high pressure is
about to collide with low pressure are called fronts. They
can often bring wild weather and are “trouble spots.”
When a cold air mass is cutting under a warm air mass and
lifting it, it is called a cold front. Its symbol on a weather
map looks similar to icicles and is usually depicted in blue.
If a warm air mass is rising up over a cold air mass, it is
called a warm front. It looks like half a sunrise on a weather
map and is usually depicted in red.
What other symbols are used on a
weather map?
There is a lot of useful information on a weather map. For example, a big, blue H
shows high pressure systems that will bring cool, dry air and light winds.
L
Low pressure systems will be shown with a big, red . They bring swirling masses of
warmer air that is moist. Stormy and windy weather is often on its way.
By reading the map legend of a weather
map, you can also see warnings of snow,
possible thunderstorms, floods, and other
dangerous conditions. You can better
prepare yourself for the weather to come.
Hazardous, or dangerous weather
conditions include things that could cause
harm or damage. We need to prepare for
things like thunderstorms with lightning,
hurricanes, and tornadoes.
Thunderstorms are often characterized
by loud rumblings, called thunder, and bright
displays of lightning. Lightning is nature’s static
electricity, and it is very powerful.
Thunderstorms can cause tornadoes, hail, flash
flooding, strong winds, and even wild fires!
Three things are needed to make a
thunderstorm:
1. Moisture
2. Unstable air
3. A lifting source
Hurricanes are huge, slow-moving
storms that are fueled by heat and energy
from warm ocean waters. They always
form over large bodies of water.
Hurricanes that blow over the warm Pacific
Ocean currents are called by another
name, typhoons. Ones that blow over the
Indian Ocean are called cyclones.
Hurricanes can cause storm surges, wind
damage, and severe flooding. They are
named after people.
In 2005, Hurricane Katrina’s storm surge brought terrible
destruction to the southern U.S. coast.
Tornadoes, also called twisters, are
dangerous, funnel-shaped columns of air that
reach from a thundercloud to the ground.
There is usually a warm air temperature.
They have winds that spin dangerously fast.
Tornadoes can be extremely dangerous
and more difficult to predict than other
storms. These strong storms can also bring
giant hailstones and torrents of rain.
A tornado’s spinning winds form a vortex that
pulls up at the center of a storm. The vortex
is a mass of spinning air.
Weather Conditions
Day
Air Temperature (°F)
Air Pressure
Day 1
25 °F
low
Day 2
80 °F
low
Day 3
30 °F
high
Day 4
65 °F
high
According to the data table above, on which day will there
most likely be a thunderstorm with heavy rain?
1.
We know that there will be snow, not rain, if the
temperature is well below freezing.
2.
We know that high pressure indicates fair, or good
weather. Low pressure indicates poor weather.
Day 2 is the day we can expect thunderstorms and heavy rain. A
warm front has come in and the air pressure is low.