5. Most collide on forward edge Some collide on backside About a million average sized droplets would be required to produce a raindrop! Terminal velocity: Almost 10 m/s for largest raindrops

6. Collisions cause coalescence… but very small droplets can avoid impact

7. Why can a cumuliform cloud produce heavier precipitation than a stratiform cloud?

8. Supercooled water droplets

9. Cumulonimbus clouds Top = ice (fuzzy cloud margins) Bottom = liquid (sharp margins) Middle = mix of ice & water

10. Ice forms directly on ice nuclei (from vapour) Promote freezing of supercooled droplets (contact nuclei) Freezing nuclei can cause freezing when immersed in a liquid drop They also promote condensation

11. Higher saturation vapour pressure Ice crystals grow at the expense of water droplets

12. The Bergeron Process Lower SVP Enough water vapour to prevent droplets from evaporating away

13. Graupel or snow pellets -supercooled droplets freeze on contact with ice crystals (riming or accretion) Snowflakes form through aggregation (ice crystals join, esp. if not too cold) As ice crystals fall…

17. Source: Desert Research Institute, Nevada, USA Source: North Dakota Cloud Modification Project, USA

25. Rain Rainshowers Raindrop shape

28. Ice pellet formation

30. Freezing Rain

31. Rime ice (review)

32. Hail Formation

33. Hail Grows by accretion (freezing of supercooled liquid droplets) Must remain in cloud for 5-10 min

45. Aguado: Understanding Weather and Climate, Fifth Edition Copyright © 2010 Pearson Education, Inc.

48. Lake Effect Snow Formation Insert Fig 7-13

49. Seasonal Lake Effect Snow Averages

50. Doppler Radar Precipitation Estimates