W ATER C YCLE The continuous movement of water on, above, and below the surface of the Earth. See pp 460 – 463 in text

W ATER C YCLE D IAGRAM T

E VAPORATION Solar energy heats Earth’s surface water and water in the soil, converting the water into vapor (gas). Sublimation – solid water is changed to water vapor (gas). The liquid phase is skipped. Transpiration – water leaves plants in the form of vapor. The warm moist air rises in the atmosphere.

W ATER I N THE A TMOSPHERE Humidity – water in the atmosphere Relative Humidity- the percentage of water that is in the air compared to the maximum amount of air the air can hold at a given temperature. A psychrometer is used to measure relative humidity.

C ONDENSATION Warm moist air cools and water is transformed into liquid water or ice crystals. Cooler air can hold less water than warmer air. Water condenses on particles in the atmosphere. Clouds form

C LOUDS 3 main types of clouds 1. Cirrus 2. Cumulus 3. Stratus Named for shape and altitude See pp 464 – 467 in text

C IRRUS Highest – above 6 km Wispy Contain ice crystals

C UMULUS Lower altitude Puffy Clear weather

N IMBOCUMULUS Anvil shaped Reaches toward stratosphere Thunderstorms

S TRATUS Low altitude Flat and cover most of sky Usually no rain

N IMBOSTRATUS Thick, dark stratus clouds May produce precipitation

F OG Clouds near the ground Forms when ground cools at night

P RECIPITATION Any form of water that falls from the clouds and hits Earth’s surface. Common types: Rain Sleet Freezing rain Snow Hail Rain gauge is used to measure rain. When measuring snow, allow the snow to melt and then measure the number of inches of liquid. See pp in text

W HAT H APPENS W HEN P RECIPITATION H ITS T HE G ROUND ? Runoff – water runs along Earth’s surface to a stream. Infiltration – water seeps into the soil Percolation – water travels down through soil and rock Aquifer – underground layer of rock that is saturated with water

W HAT A TMOSPHERIC C ONDITIONS A FFECT W EATHER ? Temperature Humidity Pressure Wind

H OW DO A TMOSPHERIC C ONDITIONS A FFECT THE W EATHER ? Air mass – a huge body of air in the lower atmosphere that has similar temperature, humidity, and air pressure. The type of air mass influences the type of weather.

T YPES OF A IR M ASSES 4 types of air masses: 1. Maritime polar Wet and cold 2. Maritime tropical Wet and warm 3. Continental polar Dry and cold 4. Continental tropical Dry and warm Label your maps See pp in text

M OVEMENT OF A IR M ASSES Air masses move in the U.S. by the prevailing westerlies and jet streams. When air masses move into an area and interact with other air masses, weather changes.

F RONTS A front is where 2 air masses meet. 4 types of fronts: 1. Cold front 2. Warm front 3. Occluded front 4. Stationary front See text pp

C OLD F RONT Cold dense air sinks under warm air. Rising, cooling warm air forms thunderstorms Moves through quickly leaving cooler air and clear skies.

W ARM F RONT Warm less dense air moves above cooler air. If air is humid, rain or snow may form. Moves more slowly than cold front, so rain may last for several days. Warmer humid weather follows front.

O CCLUDED F RONT Warm air mass is trapped between 2 cold air masses. Temperatures are cooler and rain may fall.

S TATIONARY F RONT Warm and cold air masses meet, but neither moves the other. Vapor in warm air condenses and may bring precipitation.

A IR P RESSURE – H IGH P RESSURE S YSTEM High pressure systems form when an air mass sinks to the ground. As air sinks it warms and absorbs moisture. High pressure systems bring dry, clear weather. Stationary high pressure systems can cause a drought. See p478 in text

A IR P RESSURE – L OW P RESSURE S YSTEM High pressure systems form when air rises from Earth’s surface. As the air rises and cools, it can hold less water and condensation occurs. Low pressure systems are associated with clouds, winds, and precipitation.

R EADING W EATHER M APS - S YMBOLS

R EADING A W EATHER M AP