1. WHAT IS WEATHER?
Chapter 15-1

2. I. Factors of Weather
A. Climate or Weather?
1. Climate is….
the pattern of weather over an area over many
years.
2. Weather is….
the present state of the atmosphere and describes
the current conditions. 3.

3. 4. Factors that determine the state
of the atmosphere.
a. Air pressure
b. Wind
c. Temperature
d. Amount of moisture in the air
B. Humidity
1. Water, Nitrogen and Oxygen molecules in the
atmosphere.
2. Humidity is….
the amount of water vapor held in the air.

4. 3. At 20 degrees C, the atmosphere can hold 80
3. At 20 degrees C, the atmosphere can hold
15-18g/cubic meter of moisture.
4. At 50 degrees C, the atmosphere can hold
80g/cubic meter of moisture.
5. Warm air can hold more moisture than cold air.
6. Damp, sticky summer days are a result of relative
humidity. 50

5. C. Relative Humidity
1. …is the measure of the amount of water vapor
that air is holding compared to the amount it can
hold at a specific temperature.
2. If the atmosphere is holding 40g/cubic meter of
of water vapor at 50 degrees C, the relative
humidity would be
50%.
3. Dew Point is….
the temperature at which air is saturated and
condensation takes place.

6. II. Cloud Formation
A. Clouds form when….
1. Warm air is forced upward, expands, and cools.
2. As air cools the amount of water vapor needed
for saturation decreases.
3. When relative humidity reaches 100% the air is
saturated.
4. Water begins to condense around particles in the
atmosphere.
5. Smaller water droplets become suspended in air.
6. When droplets join together clouds form.

7. III. Cloud Classification
Clouds are classified by shape.
A. Stratus Shape
1. Stratus clouds look like smooth even sheets.
2. They usually form in the lower troposphere.
3. When they are near the ground we call it FOG.
B. Cumulus Shape
1. Cumulus clouds are puffy and white.
2. They form when air currents rise.
C. Cirrus Shape
1. Cirrus clouds are fibrous and/or curly.
2. They indicate fair weather or approaching storms.

8. …and height. A. Cirro describes high elevation clouds. (6000+m)
B. Alto describes middle elevation clouds. ( m)
C. Strato describes lower clouds. (-2000m)
…and rain capacity.
A. -Nimbus clouds are associated with precipitation.
-Cumulonimbus clouds bring thunderstorms.
-Nimbostratus clouds bring long steady rain.
B. – Cirrostratus clouds are fine veils made of ice crystals.
and may form sun and moon halos.
- Altostratus are thick gray cloud sheets that bring
continuous rain.

9. Nimbus
Cumulonimbus
Nimbostratus
Cirrostratus
Altostratus

10. IV. PRECIPITATION
A. Precipitation is water that falls from the clouds.
B. Four types of participation.
1. Rain is… drops of water falling when the
temperature is above freezing.
2. Snow forms when the air temperature is so cold
that water vapor changes directly to a solid.
3. Sleet forms when snow passes through warm air,
melts and then refreezes near the ground.
4. Hail forms when water drops freeze in layers
around a small nucleus of ice.