precipitation

Question 1

what are the hazards associated with precipitation?

Answer 1

lowering of the cloud base and reduced visibility, turbulence, downbursts, and squalls

Question 2

what are the two processes of snowflake formation?

Answer 2

ice crystal process and coalescence

Question 3

how does the ice crystal process work? (how is a snowflake formed)

Answer 3

supercooled droplets mix with ice crystals as the temperature drops below -10.

mix is unstable so air becomes supersaturated in terms of frost point, resulting in evaporation of the droplets.

the ice crystals increase in size due to sublimation but when the crystals become too large for the rising currents to support them, they fall as precipitation.

Some crystals will collide with other ice crystals or with water droplets and join together to form snowflakes.

Question 4

In what part of the cloud would you expect to find ice crystals and supercooled water droplets
together?

Answer 4

high - mid latitudes.

Question 5

what is precipitation?

Answer 5

Precipitation is any liquid or frozen water that forms in the atmosphere and falls to the Earth.

Question 6

what is coalescence?

Answer 6

in tropical places, rain typically falls from clouds warmer than 0°, therefore not containing any ice crystals.

In these conditions, precipitation occurs through droplets of different sizes merging. This is coalescence

Question 7

How is coalescence enhanced?

Answer 7

Falling raindrops

Question 8

How does ___ enhance coalescence?

Answer 8

Rain droplets enhance them since the wake behind them is stirring the cloud, whirling around the small droplets. Causing increased chances of collision.

Question 9

the intensity and size of precipitation by coalescence is determined by what?

Answer 9

size of cloud and severity of updraught.

The more severe the longer the water droplet will remain in the cloud. If the cloud has great vertical extent, the droplets will have further to fall and more time to grow in size.

Question 10

define light precipitation rate and its association

Answer 10

Light rain and drizzle generally fall from thin-layer clouds. (rate = less than 2.5mm per hour)

Question 11

define moderate precipitation rate and it’s association

Answer 11

usually associated with thick Nimbostratus clouds of significant vertical extent, (rate = 2.5 - 7.6mm per hour)

Question 12

define heavy precipitation rate and it’s association

Answer 12

Heavy precipitation, rain, and hail is always associated with thick Cumulus clouds of great vertical extent - (Rate >7.6mm per hour)

Question 13

what is the relationship between precipitation rate and dewpoint temperature/mixing ratio?

Answer 13

The exponential relationship of dew point temperature and mixing ratio leads to heavier precipitation in warm climates.

Question 14

what is the relationship between cloud height and precipitation?

Answer 14

higher clouds will have a greater area concentration of water droplets.

The drops will, therefore, accumulate a greater mass before falling to the ground.

Question 15

what is the relationship between unstable cloud and precipitation?

Answer 15

Unstable clouds with a strong updraught will retain water droplets in the cloud for a longer
period of time.

Question 16

what happens to precipitation if the temperature is below -10 degrees?

Answer 16

precipitation will occur due to the ice crystal process.

Question 17

what happens to precipitation if the temperature is above -10 degrees?

Answer 17

few ice crystals exist so raindrops can

only form by coalescence - producing light rain

Question 18

what is virga?

Answer 18

precipitation falling from the base of the cloud that evaporates before it reaches the Earth’s surface.

Question 19

is virga reported in METARS?

Answer 19

no

Question 20

what does virga produce?

Answer 20

Virga produces large masses of colder air that fall

Question 21

why are virga downbursts bad?

Answer 21

Down-bursts can be dangerous because of severe turbulence and windshear near the ground

Question 22

where can you find the effects of virga normally?

Answer 22

These phenomena are reported in SIGMET hazardous weather reports, ATIS, or VOLMET

Question 23

what is an ice pellet and how do they occur?

Answer 23

hard grains of ice, that occur when rain falls from warm air through a layer where the temperature is below zero

Question 24

what is hail?

Answer 24

precipitation in the form of irregular lumps of ice

Question 25

what size does hail come in and what are they normally associated with?

Answer 25

size varies from 2 and 5mm, to large hail up to 50mm. Normally associated with thunderstorms

Question 26

what is rain?

Answer 26

liquid water droplets heavier than drizzle

Question 27

what is sleet?

Answer 27

a mixture of snow and rain

Question 28

how are sleet proportions determined?

Answer 28

The proportions are determined by the temperature of the air. Icing conditions are likely with sleet.

Question 29

what are snow grains?

Answer 29

small white opaque grains falling from stratus clouds or supercooled fog.

Question 30

what is drizzle?

Answer 30

uniform precipitation consisting of minute drops which seem to float in the air.

Question 31

what happens to drizzle if the temperature falls below 0 degrees?

Answer 31

it’ll be freezing drizzle and icing conditions may exist.

Question 32

what is snow?

Answer 32

precipitation in the form of branched ice crystals.

Question 33

what is continuous rain?

Answer 33

rain that happens all the time without stopping, or seems to do so.

Question 34

what are showers?

Answer 34

a brief and usually light fall of rain, hail, sleet, or snow.

Question 35

what is intermittent rain?

Answer 35

not happening regularly or continuously; stopping and starting repeatedly or with periods

Question 36

what are the three categories of precipitation?

Answer 36

frontal, stable air masses and unstable air masses

Question 37

what is a frontal system in terms of precipitation?

Answer 37

When precipitation falls from a widespread and extensive cloud system

Question 38

what type of precipitation is associated with stable air masses?

Answer 38

Drizzle, and freezing drizzle or snow grains

Question 39

what type of precipitation is associated with unstable air masses?

Answer 39

Showers of rain or sudden changes in intensity