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What is the Weather
-the state of the atmosphere at a specific time and place.
What does it tell us?Weather describes conditions such as air
pressure, wind, temperature and the amount of moisture in the air.
How weather forms?1. The sun provides almost all the
Earth’s energy. Energy from the sun evaporates water into the atmosphere where it forms clouds.
2. The sun is a source of heat energy which is absorbed by the earth’s surface, that heats the air above it.
3. Weather is the result of heat and earth’s air and water.
Air TemperatureAir- molecules that are always moving
randomly even when there’s no wind.Temperature- a measure of the average
amount of motion of molecules.
Hi temperatures = rapidly moving molecules
Lo temperatures = slow moving molecules
Wind- Air moving in a specific direction.
Warm air -> low atmospheric pressureCold air -> high atmospheric pressure
How wind formsAir moves from regions of high pressure
to regions of low pressure.
Humidity- The amount of water vapor present in
the air.
Saturation- when water vapor present in the air for condensation
Relative Humidity
- A measure of the amount of water vapor present in the air compared to the amount needed for saturation at a specific temperature.
Ex. if the relative humidity is 50% => the air contains 50% of the water needed for the air to be saturated.
Dew Point- The temperature at which air is
saturated and condensation forms.
When air near the ground cools to its dew point, water vapor condenses and forms dew (fog).
When dew is cooled to 00C frost may form.
Forming Clouds1. Warm air is forced upward, expands and
cools.(conduction) 2. Air cools (convection), the amount of water
vapor needed for saturation decreases (dew point) and the relative humidity increases.
3. Relative humidity reaches 100% saturated.4. Water vapor soon begins to condense in tiny
droplets around small particles such as dust and salt.
5. The billions of droplets suspended in the air form clouds.
Stratus- Clouds that form layers, or smooth, even sheets in the
sky.
- Form at low altitudes and may be associated with fair weather or rain or snow.
- Dew point sometimes form stratus clouds near the ground called fog.
Cumulus- Masses of puffy, white clouds, often
with flat bases.- Sometimes tall to great heights and
associated with fair weather and thunderstorms.
CirrusFibrous or curly, high, thin, white, feathery
clouds made of ice crystals.Associate with fair weather, but can indicate
storms approaching.