National Weather Service weather thresholds (e.g. conditions change from visual meteorological conditions to instrument meteorological conditions). The basic weather elements observed are: sky condition, visibility, present weather, obstructions to vision, pressure, temperature, dew point, wind direction and speed, precipitation accumulation, and selected significant remarks. The coded observations are issued as METARs and look similar to this: Getting more information on the atmosphere, more frequently, and from more locations is the key to improving forecasts and warnings. Due to the large installation and operating costs associated with ASOS, the stations are widely spaced. Therefore, the Cooperative Observer Program (COOP), a network of approximately 11,000
Foehn wind it expands and cools due to the decrease in pressure with height. Since colder air can hold less water vapour, moisture condenses to form clouds and precipitates as rain or snow above the mountain's upwind slopes. The change of state from vapour to liquid water is accompanied by heating, and the subsequent removal of moisture as precipitation renders this heat gain irreversible, leading to the warm, dry foehn conditions in the mountain's lee. This mechanism has become a popular textbook example of atmospheric thermodynamics and it lends itself to attractive diagrams. However the common occurrence of 'dry' foehn events, where