Precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor, most often from clouds, that is pulled down by gravity and deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel.
Rain
| Rain is liquid precipitation (water droplets) and the most frequent type of precipitation on earth. Rain requires: 1. the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface. 2. the condensation of atmospheric water vapor into drops of water heavy enough to fall, often making it to the surface. Two processes, possibly acting together, can lead to air becoming saturated leading to rainfall: cooling the air or adding water vapour to the air. |
Snow
| Snow is a type of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The ice crystals, less than 0.1 mm largely, developing thereby, fall by increasing weight and continue to increase by the difference of the vapour pressure between ice and undercooled water. Also, the water vapour contained in air resublimates, thus transforming directly into ice and thereby contributing to the crystal growth. Snowfall amount and its related liquid equivalent precipitation amount are determined using a variety of different rain gauges. As a rule of thumb, 10 centimeters of snowfall corresponds to 1 cm of water. |
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| Snowflakes fall in a variety of sizes and shapes. They are hexagonal: because of the special structure of the water molecules, only angle of 60° and/or 120° is possible. Every snowflake is different - there are no identical shapes. |
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JungfraujochOn the SnowMeteogramm to the right, you see the current weather forecast for the area of the Jungfraujoch (Switzerland). The average elevation of the area is 2826m asl (meters above sea level). The graphic shows the predicted temperature gradient in different elevations. The lower part of graphic shows the predicted total precipitation, the snow height and the change (increase or decrease) of the snow height. | 
meteogram SN☼W:
Jungfraujoch (46.55°N / 7.98°E) |
| In the following you can see the RainNow forecasts for four different locations of the 29.07.2010. They show the precipitations all 15 minutes for the last two hours and the prospective hours. Now take a look at the forecast of the Jungfraujoch and memorize the position of the precipitaion areas ( dark coloured areas). Take a look on the card. Here, the Mountain Jungfraujoch is in the center (A). This card shows - like the RainNow frecast of the Jungfraujoch- the surroundings in 25 km distance. Name the locations, where it shall resp. has already rained. Now compare the forecasts with the RainNow forecasts of the surrounding locations for which there ar also RainNow forecasts. Example: The RainNow forecast of the Jungfraujoch says that there will be showers from 07:00, but not before. ( There are blue areas from 07:00 o`clock) Now we take a look at the card (right handside). Mörel is a location in the South. Now take a look at the RainNow forecast of Mörel. Mörel is in the center of the square area. So the center has to be coloured in blue since 07:00. Before it didn`rain in Mörel. So, the center mustn`t be coloured in blue till 07:00. In this way you can comprehend, in which locality it will rain or not. |
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RainNow Vorhersagen vom 29.07.2010: Anklicken zum Vergrößern
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