Definition of precipitate:
Condensation results in droplets - 0.05-0.1 mm in size
Collisions of these droplets increases droplet size to 0.5 mm - drizzle
Continued collisions increase size to 1-2 mm - rain
Ice crystals also form in clouds - supercooled droplets of water collide with a particle, causing the water to crystallize.
Once ice crystal grows large enough to fall it will be deposited as snow or rain (if the ice melts before reaching the surface).
Crystals of water - technically defined as minerals.
Different crystals form at different temperatures
Sleet - raindrops falling through a cold layer of air become partially or completely frozen.
Ice Storms - supercooled raindrops come into contact with surfaces that are below 0°C and freeze on that surface.
Hail - ice crystals formed in convection cells in thunderstorms.
Precipitation is measured in units of depth of fall per unit time.
Commonly reported as inches per day, inches per month, inches per year or metric units.
One inch of rainfall would cover the ground with one inch deep water if it did not run off, evaporate or soak into the ground.
Rain gauge is used to collect and measure rain fall.
Snow fall is measured by melting the collected snow and getting a rainfall depth. (This is not how it is reported on the News, but is how it is measured for monthly or annual precipitation records)
Three processes of precipitation
1) Orographic precipitation
2) Convectional precipitation
3) Cyclonic precipitation
Moist air is forced up and over a mountain range.
As the air rises it cools adiabatically.
Condensation begins when the air mass has reached the dew point temperature.
As the air mass continues to rise, precipitation will occur if there is sufficient moisture in the air.
The air mass continues to cool, but along the Wet Adiabatic Lapse Rate.
Once the air mass reaches the summit, it begins descending the lee side of the range.
The air becomes compressed as it descends, warming along the Dry Adiabatic Lapse Rate.
The air mass at the end of its move over the mountain range is warmer and drier than the air when it started.
Moist air rises due to heating.
As the air rises it cools adiabatically.
Condensation begins when the air mass has reached the dew point temperature.
As the air mass continues to rise, precipitation will occur if there is sufficient moisture in the air.
The air mass continues to cool, but along the Wet Adiabatic Lapse Rate.
Once the air mass temperature equals that of the surrounding air mass, it will stop rising.
Latent heat release is the key to convectional precipitation - causes the air to remain warm and continues to rise.
Strongest form of convectional precipitation.
These are intense local storms associated with tall, dense, cumulonimbus clouds with strong updrafts and downdrafts.
Often these storm consist of multiple convection cells.
Heights of the clouds can be 6-12 kilometers.
Intense precipitation, hail and lightning are common.
Hail - ice pellets which form in the convection cells.
