2 Key TermsEvaporation – the process by which water molecules escape into the air.Humidity – water vapor or moisture, in the air.Relative humidity – the percent of moisture the air holds relative to the amount it could hold at a certain temperature.
3 Measuring Relative Humidity Psychrometer – device used to measure relative humidity.Consists of 2 thermometers.One is covered with a moist cloth.When air passes over wet cloth, water evaporates and temperature cools.
4 Measuring Relative Humidity Differences in temperature between 2 bulbs is used to determine relative humidityCompare temp difference (degrees difference) to dry thermometer tempLook up relative humidity in chart
5 CloudsForm when moisture in the air condenses on small particles of dust or other solids in the air.Mixture in which particles of water are suspended in air.
6 Cloud Formation Warm air can hold more moisture than cold air. As air rises it cools.Air becomes saturated with water.Holds maximum amount of water.Water vapor in air condenses clouds form.Dew point – the temp. at which water vapor condenses.
7 Cumulus clouds “Fluffy” clouds Flat bottom Usually indicate fair weatherCan produce thunderstorms
8 Stratus Clouds Smooth, gray Cover the entire sky Associated with light rain and drizzleWhen close to ground fog
9 Cirrus Clouds Thin and feathery, made of ice crystals Can be seen in fair weatherMay indicate that rain or snow will fall in several hours.A.k.a. – mares’ tails
10 Special Types of Clouds Cirrostratus -high-level clouds composed of ice crystalscan cover the entire skyrelatively transparent, as the sun or the moon can easily be seen through themCumulonimbus – thundercloudsNimbostratus - dark, low-level clouds accompanied by light to moderately falling precipitation
11 Precipitation Water vapor that condenses and falls to Earth Formation: Ex. – rain, sleet, snowFormation:Cloud droplets increase in size by colliding and combining with other dropletsDroplets become to heavy, and are pulled down by gravity
12 Snow Forms when water vapor turns directly into a solid 6-sided flakes (ice crystals)
13 Hail Forms in cumulonimbus clouds Small chunks of ice Formed when water droplets hit ice pellets in clouds and freezeCan be held in clouds by winds and grow in size before falling
14 Measuring Rainfall Rain gauge Straight sided container with flat bottomCollects rain over a given period of timeUsually measure in mm or cm