Precipitation Flashcards
Ice Crystal Process (Bergeron)
Occurs in clouds below 0C, containing a mixture of supercooled water droplets and ice. Ice crystals build via sublimation and collisions and end up growing larger. The Ice crystals are eventually large enough to fall. If the base of the cloud is above freezing, the crystals melt and it falls as rain. If it it below freezing, it falls as ice pellets.
Coalescence Theory
Explains formation of precipitation in clouds warmer than 0C. Everything starts out as a water droplet. Updraughts forces the droplets to collide and join together until they are large enough to fall.
Cloud Droplet Size
0.02mm
Drizzle (DZ)
Falls from which cloud?
Size of drizzle droplets?
Max terminal velocity?
Falls from stratiform clouds.
Size: Up to 0.5mm.
Max Terminal velocity 4m/s.
Rain (RA)
Size?
Terminal velocity?
0.5mm to 5.5mm
Terminal velocity: 9m/s
Snow (SN)
Temperature range?
Largest snowflake occurs at which temperature?
Falls in temps between +4C and -5C.
Largest flakes are 0C.
Snow Grains (SG) Falls from which cloud?
Opaque grains of Ice up to 1mm.
Falls from Stratiform clouds.
Snow Pellets (Soft Hail)
Size?
Falls from which cloud?
Impact with ground?
Conical 2-5mm.
Break on contact with ground.
Falls from Cumuliform clouds.
Ice Pellets (PL)
Shape?
Color?
Falls from which cloud?
Conical shape
Clear Ice
Bounce on impact with ground
Falls from Ns or thick As.
Small Hail
Size and METAR abbreviation?
(GS)
less than 5mm.
Large Hail
Size and METAR abbreviation?
(GR)
larger than 5mm.
Hail comes from which cloud?
Cb
Intensity of rain.
Slight/Moderate/heavy.
(mm/hour)
Slight: less than 0.5mm/hr
Mod: 0.5-4mm/hr
Heavy: more than 4mm/hr
Continuous Precipitation
No breaks in precipitation for more than 60 minutes. Only falls from Stratiform clouds.
Intermittent Precipitation
Precipitation falls from time to time less than 60 minutes. Falls from stratiform clouds.
