1	Chapter 12: Freezing Precipitation and Ice Storms
2	Weather / E. Rocky Cyclone
3	Precipitations
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5	Growth by Condensation
6	Collision Collector drops collide with smaller drops. Due to compressed air beneath falling drop, there is an inverse relationship between collector drop size and collision efficiency. Collisions typically occur between a collector and fairly large cloud drops. Smaller drops are pushed aside. Collision is more effective for the droplets that are not very much smaller than the collect droplet.
7	Coalescence When collisions occur, drops either bounce apart or coalesce into one larger drop. Coalescence efficiency is very high indicating that most collisions result in coalescence. Collision and coalescence together form the primary mechanism for precipitation in the tropics, where warm clouds dominate.
8	Freezing Precipitation Freezing precipitation is rain or drizzle that freezes on surfaces and leads to the development of an ice glaze. Freezing precipitation is responsible for about 20% of all winter weather-related injuries. Freezing precipitation occurs in about a fourth of all winter weather events in the continental US. Ice storm is defined as a freezing precipitation weather event with ice accumulation of at least 0.25 in (0.64cm). Half of the freezing precipitation events qualify as ice storms.
9	Supercooled Water Ice melts at 0°C, but water does not necessary freeze to ice at 0°C. Ice nuclei is needed to help water to get frozen. Certain microscopic particles, such as clay, organic particles, or bacteria, have a crystalline structure similar to ice that can allow water molecular to attach to and to build an ice lattice. Without enough ice nuclei, water can exist event its temperature is below between 0°C and -40°C, which are called “supercooled water”. Supercooled water can result in freezing precipitation when they come in contact with a surface that has a temperature below 0°C.
10	Two Ways to Produce Freezing Precipitation Melting Process è freezing rain When snow falls from high in the clouds into an atmospheric layer where the temperature exceeds 0°C. Supercooled Warm Rain Process è freezing drizzle This process occurs in low clouds, where rain is formed through collision and coalescence without involving snow (that is why it is called warm rain).
11	Cross Section through a Warm Front
12	Weather / E. Rocky Cyclone
13	Freezing Rain and Sleet
14	Freezing Drizzle
15	Freezing Drizzle and Aviation Safety
16	Weather Patterns for Freezing Precipitation
17	Cold Air Damming
18	Forecasting Freezing Precipitation Vertical soundings of temperature and moisture are crucial. It is particularly important to pay attention to the presence of any above-freezing layers in the lowest few kilometers.
19	Distribution of Freezing Rain
20	Distribution of Freezing Drizzle