WHAT IS WEATHER?WHAT IS WEATHER?

Chapter 15-1Chapter 15-1

I. Factors of WeatherI. Factors of Weather

A. Climate or Weather?A. Climate or Weather?

1. Climate is….1. Climate is….

the pattern of weather over an area over the pattern of weather over an area over manymany

years.years.

2. Weather is….2. Weather is….

the present state of the atmosphere and the present state of the atmosphere and describesdescribes

the current conditions.the current conditions.

3. 3.

4. Factors that determine the state4. Factors that determine the state

of the atmosphere.of the atmosphere.

a. Air pressurea. Air pressure

b. Windb. Wind

c. Temperaturec. Temperature

d. Amount of moisture in the aird. Amount of moisture in the air

B. HumidityB. Humidity

1. Water, Nitrogen and Oxygen molecules in 1. Water, Nitrogen and Oxygen molecules in thethe

atmosphere.atmosphere.

2. Humidity is…. 2. Humidity is….

the amount of water vapor held in the air.the amount of water vapor held in the air.

3. At 20 degrees C, the atmosphere can hold3. At 20 degrees C, the atmosphere can hold 15-18g/cubic meter of moisture.15-18g/cubic meter of moisture.4. At 50 degrees C, the atmosphere can hold4. At 50 degrees C, the atmosphere can hold 80g/cubic meter of moisture.80g/cubic meter of moisture.5. Warm air can hold more moisture than cold 5. Warm air can hold more moisture than cold

air.air. 6. Damp, sticky summer days are a result of 6. Damp, sticky summer days are a result of

relativerelative humidity.humidity.

50

80

C. Relative HumidityC. Relative Humidity1. …is the measure of the amount of water vapor1. …is the measure of the amount of water vapor that air is holding compared to the amount it that air is holding compared to the amount it

cancan hold at a specific temperature.hold at a specific temperature.

2. If the atmosphere is holding 40g/cubic meter of2. If the atmosphere is holding 40g/cubic meter of of water vapor at 50 degrees C, the relative of water vapor at 50 degrees C, the relative humidity would be humidity would be

50%.50%.

3. Dew Point is….3. Dew Point is…. the temperature at which air is saturated andthe temperature at which air is saturated and condensation takes place.condensation takes place.

II. Cloud FormationII. Cloud Formation

A. Clouds form when….A. Clouds form when….

1. Warm air is 1. Warm air is forced upwardforced upward, , expandsexpands, and , and coolscools..

2. As air cools 2. As air cools the amount of water vapor neededthe amount of water vapor needed

for saturationfor saturation decreases. decreases.

3. When relative humidity reaches 3. When relative humidity reaches 100%100% the air is the air is

saturatedsaturated..

4. Water begins to 4. Water begins to condense around particles in thecondense around particles in the

atmosphereatmosphere..

5. Smaller water droplets become 5. Smaller water droplets become suspended in airsuspended in air..

6. When droplets join together6. When droplets join together cloud clouds form.s form.

III. Cloud ClassificationIII. Cloud Classification

Clouds are classified by shape.Clouds are classified by shape.

A. Stratus ShapeA. Stratus Shape

1. Stratus clouds look like 1. Stratus clouds look like smooth even sheets.smooth even sheets.

2. They usually form in the 2. They usually form in the lower tropospherelower troposphere..

3. When they are near the ground we call it 3. When they are near the ground we call it FOGFOG..

B. Cumulus ShapeB. Cumulus Shape

1. Cumulus clouds are 1. Cumulus clouds are puffy and whitepuffy and white..

2. They form 2. They form when air currents risewhen air currents rise..

C. Cirrus ShapeC. Cirrus Shape

1. Cirrus clouds are 1. Cirrus clouds are fibrous and/or curlyfibrous and/or curly..

2. They indicate 2. They indicate fair weather or approaching fair weather or approaching stormsstorms..

……andand height.height.A. Cirro describes A. Cirro describes high elevationhigh elevation clouds. (6000+m) clouds. (6000+m)B. Alto describes B. Alto describes middle elevationmiddle elevation clouds. (2000- clouds. (2000-6000m)6000m)C. Strato describes C. Strato describes lower cloudslower clouds. (-2000m). (-2000m)

……and rain capacity.and rain capacity.A. -A. -NimbusNimbus clouds are associated with clouds are associated with precipitationprecipitation.. --CumulonimbusCumulonimbus clouds bring clouds bring thunderstormthunderstorms.s. --NimbostratusNimbostratus clouds bring clouds bring long steady rain.long steady rain.

B. – B. – CirrostratusCirrostratus clouds are clouds are fine veils made of ice fine veils made of ice crystals.crystals.

and may and may form sun and moon halosform sun and moon halos.. - - AltostratusAltostratus are are thick gray cloud sheetsthick gray cloud sheets that bring that bring

continuous raincontinuous rain..

• NimbusNimbus

• CumulonimbusCumulonimbus

• NimbostratusNimbostratus

• CirrostratusCirrostratus

• AltostratusAltostratus

IV. PRECIPITATIONIV. PRECIPITATION

A. Precipitation is water that falls from the clouds.A. Precipitation is water that falls from the clouds.

B. Four types of participation.B. Four types of participation.

1. Rain is… drops of water falling when the 1. Rain is… drops of water falling when the

temperature is above freezing.temperature is above freezing.

2. Snow forms when the air temperature is so 2. Snow forms when the air temperature is so cold cold

that water vapor changes directly to a solid.that water vapor changes directly to a solid.

3. Sleet forms when snow passes through warm 3. Sleet forms when snow passes through warm air, air,

melts and then refreezes near the ground.melts and then refreezes near the ground.

4. Hail forms when water drops freeze in layers 4. Hail forms when water drops freeze in layers

around a small nucleus of ice. around a small nucleus of ice.