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
Weather window than 72 hours can be defined as weather-limited operations. These operations can be planned independently of statistical data and based only on weather forecasts. For weather-limited operations, critical factors such as forces, movements and acceleration shall be calculated in a rather worse weather condition (design criterion) than the weather in which it is planned to perform the operation (operational criterion). This is due to the unreliability of weather forecasts. The longer the planned operation lasts, the greater the difference between the operational criterion and the design criterion. The relationship between the operational criterion and the design criterion is defined as