Clouds and Precipitation

Part 1: Clouds and Cloud Formation

Formation A cloud is a collection of small water droplets or ice crystals Water vapor must condense on some solid particle, called a condensation nucleus, which can be dust, pollen, smoke, or other material.

Adiabatic Cooling Temperature drops about 1ºC for every 100 meters increase in elevation, or gains 1ºC for every drop in 100 meters. This is called adiabatic lapse rate. When the drop in temperature hits the dew point, and condensation begins, it is called the condensation level.

Advective Cooling Cooling that occurs when a colder air mass impacts a warmer mass creating clouds. Or when warmer air moves over a cooler surface (important in lake effect.)

Naming Clouds Cloud names are made up of prefixes, suffixes, and root words, all modifying the type of cloud. Stratus means layered, tend to be low Cumulus means heaped or piled Cirrus means curly, tend to be high Nimbus means rain Alto means mid-level and is exclusively a prefix (not a cloud type by itself)

Modified cloud names: Altostratus Nimbostratus Altocumulus Stratocumulus Cumulonimbus Cirrostratus Cirrocumulus

(Mare’s Tails)

Fog Described as a “cloud on the ground” but it forms differently than clouds. Radiation fog forms in valleys when cool air sinks and is cooled below the dew point. Advection fog forms when warm moist air moves over cooler land (lakes and oceans.)

Part 2: Precipitation

Four main types of precipitation: 1) Rain liquid precipitation. May start frozen, but is completely liquid when it reaches surface Drizzle is rain drop smaller than 0.5mm Freezing rain is liquid until it get into cold surface air and freezes onto things on the ground. Ice storms are caused by freezing rain.

Four main types of precipitation: 2) Sleet rain that has completely frozen on the way down as it passes through a colder layer of air.

Four main types of precipitation: 3) Hail water that is frozen, passes through a warmer layer of air, gets coated with water, is blown back up into a cloud to refreeze, then get coated with more layers water, to finally fall out of the cloud

Four main types of precipitation: 4) Snow solid precipitation that forms from water vapor condensing directly to the solid state. Forms below 32ºF (0ºC) Shape, size, and kind of snow is determined by the temperature at which the water vapor condenses to solid