The Weather

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 Temperature Air- 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 pressure Cold air -> high atmospheric pressure How wind forms Air moves from regions of high pressure to regions of low pressure.

Instruments that measure wind

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 0 0 C frost may form.

Forming Clouds 1.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.

Classifying 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.

Cirrus Fibrous or curly, high, thin, white, feathery clouds made of ice crystals. Associate with fair weather, but can indicate storms approaching.

Atmosphere Earth’s air, which is made up of a thin layer of gases, solids and liquids: forms a protective layer around the planet and is divided into five distinct layer.