Slide1: Weather *The current state of the atmosphere *Weather is caused by the interaction of air, water and Sun. *Factors that determine the weather are wind, temperature, air pressure,amount of moisture in the air *The water cycle forms the basis of our weather


Slide2: Humidity *The amount of water vapor held in the air. (like a sponge; water vapor molecules fit into spaces between air molecules) *The amount of water vapor in the air depends on the temperature


*Low humidity: Cool air-slows down molecules-condensation(rain) *High humidity: Warmer air-faster air(too fast for condensation) water molecules remain as water vapor: *Low humidity: Cool air-slows down molecules-condensation(rain) *High humidity: Warmer air-faster air(too fast for condensation) water molecules remain as water vapor


Slide4: Relative Humidity *The amount of water vapor in air compared to amount it can hold at a certain temperature *When air holds all it can it is Saturated *50% relative humidity means air is half saturated *100% relative humidity means air is saturated


Slide5: *The temperature that water is saturated and begins to condensate is known as the dew point(water on the outside of a glass, morning dew)


Slide6: Cloud Formation *Warm air is forced up, expands, and cools *Air cools,water vapor needed for saturation decreases, relative humidity increases *RH reaches 100% and air becomes saturated


Slide7: *Vapor begins to condense in tiny drops around small particles of dust, smoke, or salt *These drops are so tiny they become suspended in the air *When millions of these drops form they become clouds


Slide8: Cloud Classification *Classified mainly by shape and height *Three main cloud types: Stratus-smooth even sheets-low altitudes- fair weather and precipitation *When air is cooled to its due point and condenses near the ground, it forms a stratus cloud called FOG


Slide9: Cumulus clouds are masses of puffy white clouds(cauliflower clouds) *Form when air currents rise *Tower to great heights *Associated with fair weather and thunderstorms Cumulus Clouds


Slide10: Cirrus Clouds *Appear to be fibrous or curly *High thin feathery *Contain ice crystals *Associated with fair weather *May indicate approaching thunderstorms


Slide11: Cloud Height Prefix *Cirro-describes high clouds-base starts at 6000 meters *Alto-describes middle elevation clouds- base is between 2000 and 6000 meters *Strato-refers to clouds below 2000 meters


Slide12: Cirrostratus Clouds Cirro-high clouds,Stratus-smooth even sheets(look like high ,fine veils) Altostratus Alto-middle elevation,Stratus-smooth even sheets(They look like thick veils)


Slide13: Rain Capacity Nimbus:dark clouds-associated with precipitation-full of water Cumulonimbus:when a nimbus cloud is also a towering cumulus cloud-up to 18000m-associated with thunderstorms Nimbostratus:dark-smooth-associated with long steady rain


Slide14: Precipitation *Water falling from the clouds *Above freezing is rain *When temperature are below freezing- Water vapor changes directly to a solid called snow *Snow falls through warm air & melts-then goes through cold air & freezes ---sleet *Hail-ice tossed by rising and falling currents-builds layers


Slide15: Changes in weather Always changing because of movement of air and moisture Air Masses: A large body of air with properties of surface where it developed Land-dry Water-wet Tropics-warm Poles-cold


Slide16: Pressure Systems Determined by temperature,density (height),and water vapor in the system High Pressure System-descending (sinking)air-difficult for air to rise and make clouds-usually means good weather Low Pressure System –ascending air forms clouds


Slide17: Fronts *Boundary between two air masses *Storms and Precipitation *Air from High Pressure moves into Low *Forces warm air up *Forms clouds *Where air masses meet that have different properties, the air does not mix *4 types of fronts


Slide18: Cold:cold air goes under warm air-violent storms-faster than warm front Warm:warm air slides over cold air-Wide bands of rain Stationary:a warm and cold front meet And stop moving-stays several days-Rain across entire frontal area Occluded:2 cold air masses meet forcing Warm air up-strong wind and heavy rain


Slide19: Thunderstorms *Heavy rain causes downdrafts associated with strong wind *Positive and negative charges in the clouds cause lightning *Thunder - a result of rapid expansion of air molecules moving back and forth form sound waves *89kph winds =severe thunderstorms


Slide20: Tornadoes *Violent whirling wind moves over land generally southwest to northeast *Form along a front *Winds up to 500kph *Updraft can lift animals,cars, and houses *Rarely over 200 meters in diameter and only last a few minutes


Slide21: Hurricanes *The most powerful storm *Large swirling low pressure system *Forms over tropical oceans *Turns heat energy from ocean into wind *Loses energy over land-no warm moist rising air to fuel the storm *Northern hemisphere -counterclockwise *Swirl forms from southeast and northwest trade winds


Slide22: Weather Forecasting *Meteorologist studies the weather *He measures temperature,air pressure, wind,humidity,and precipitation *He uses computers,satellites,weather balloons,and Doppler Radar *Uses information to make weather maps *Uses maps to make forecasts


Slide23: Weather Information *Station Model-shows weather condition for specific location(example page 479) (see page 825) *A line that connects points of equal temperature is an isotherm( like topo-map) *A line that connects points of equal air pressure is an isobar *Weather fronts move from from west to east in the U.S.


Slide24: That’s about it when it come to Predicting exactly what the weather is going to do Can we change the weather? *Plant trees--------changes wind *Mulch----reduces moisture loss *Release smoke,gases into atmosphere, build cities,cut forests,build lakes--- changes wind,temperature and moisture