1. Clouds and Precipitation

2. Clouds
Visible masses of tiny water droplets or ice particles suspended in the atmosphere.
3 variables must be present for clouds to form.
Water vapor: air must be saturated.
Cool temperatures: air must be cooled to the dew point.
Condensation nuclei: provides a surface for condensation to occur.
Ex. : dust, salt, smoke.

3. Cloud formation As warm air rises and expands, it cools.
When air reaches a level where its temperature is lower than dew point, condensation occurs to form a cloud.
The level where condensation
forms is called the
condensation level.
The base of the cloud
forms here

4. What causes air to rise?
Mountains(Orographic Lifting) - Air hits mountains and is forced up
If one side gets all rain, what happens to other?

5. What causes air to rise?
Frontal Wedging- cool air acts as barrier over which warmer, less dense air rises

6. What causes air to rise?
Convergence- as air of the same density collides since it cannot be forced down, so it is forced up
Localized Convection- unequal heating of the Earth causes differences in density

7. Stability Rising moving air = Unstable Air
Warm air rises into cold air.
Non- moving air = Stable Air
Warm air above cold air
Called inversion

8. Cloud Types

9. Cloud Types
Clouds are classified on the basis of their form and height.
Form
Cirrus – “hair like”, high altitude, wispy
Cumulus – “pile/pillow”, rounded
Stratus – “ layer”, sheets or layered, no distinction between individual clouds

10. Cloud Types Height High Clouds- Cirrus, Cirrostratus, Cirrocumulus
What do you notice?
Middle Clouds- Altostratus, altocumulus
Low Clouds- Stratus, stratocumulus, nimbostratus, nimbus = “rainy cloud”
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11. High Clouds
Cirrus
Cirrostratus
Cirrocumulus

12. Middle Clouds
Altocumulus
Altostratus

13. Low Clouds
Stratus
Stratocumulus
Nimbostratus

14. Vertical Clouds
Some clouds do not fit into one layer, these cloud can build to towering heights.
Cumulus – puffy cloud usually found at low cloud levels
Cumulonimbus- formed from rising of unstable air
Often associated with thunder, lightning, and hail

15. Cumulonimbus

16. Mammatus Cloud – Occasionally found with cumulonimbus clouds

17. 3 4 5 12 2 6 7 1 8 9 10 11

18. Fog
Fog – a cloud at the surface of the Earth

19. Precipitation
Any moisture that falls from the air to the earth’s surface.

20. How rain forms Collision-Coalescence Step 1: Large water drop falls
Step 2: More drops are added
Step 3: Splat

21. Types of Precipitation
What kind of precipitation you receive depends upon if the water that falls freezes or melts during descent.
Drizzle: smaller water droplets
Rain: water is melted when it hits ground
Snow: water is frozen and stays frozen
Sleet: water freezes in mid-fall
Freezing Rain(glaze): water freezes upon impact
Hail: water is frozen as pellets and pellets grow in clouds.

22. Cloud Seeding Method used to cause or increase precipitation.
Achieved by adding condensation nuclei to clouds