Most collide on forward edge Some collide on backside About a million average sized droplets would be required to produce a raindrop! Terminal velocity:

•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

Collisions cause coalescence…

but very smalldroplets can avoid impact

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

Supercooled water droplets

Cumulonimbus clouds

Top = ice (fuzzy cloud margins)

Bottom = liquid(sharp margins)

Middle = mix of ice & water

•Ice forms directly on ice nuclei (from vapour)

•Promote freezing of supercooled droplets(contact nuclei)•Freezing nuclei can cause freezing whenimmersed in a liquid drop•They also promote condensation

Higher saturation vapour pressure

Ice crystals grow atthe expense of waterdroplets

The Bergeron Process

Lower SVP Enough water vapour to prevent droplets from evaporating away

Graupel or snow pellets -supercooled dropletsfreeze on contact withice crystals (riming or accretion)

Snowflakes form through aggregation(ice crystals join,esp. if not too cold)

As ice crystals fall…

Source: Desert ResearchInstitute, Nevada, USA

Source: North Dakota Cloud Modification Project, USA

Source: North Dakota Cloud Modification Project, USA

Rain • Rainshowers • Raindrop shape

Ice pellet formation

Freezing Rain

Rime ice (review)

Hail Formation

Hail

Grows by accretion(freezing of supercooledliquid droplets)

Must remain in cloud for 5-10 min

Munchique National ParkForest Ranger Station, Sector 20 de Julio2150 masl

Rain Gauge

Aguado: Understanding Weather and Climate, Fifth Edition Copyright

© 2010 Pearson Education, Inc.

Aguado: Understanding Weather and Climate, Fifth Edition Copyright

© 2010 Pearson Education, Inc.

Lake Effect Snow Formation

Insert Fig 7-13

Seasonal Lake Effect Snow Averages

Doppler Radar Precipitation Estimates