![]() The global models are run outwards to varying times into the future. Time steps for global models are on the order of tens of minutes, while time steps for regional models are between one and four minutes. This time stepping is repeated until the solution reaches the desired forecast time. These rates of change predict the state of the atmosphere a short time into the future the time increment for this prediction is called a time step. These equations are initialized from the analysis data and rates of change are determined. Additional transport equations for pollutants and other aerosols are included in some primitive-equation mesoscale models as well. These equations-along with the ideal gas law-are used to evolve the density, pressure, and potential temperature scalar fields and the velocity vector field of the atmosphere through time. Within any modern model is a set of equations, known as the primitive equations, used to predict the future state of the atmosphere. AutomatedĪtmospheric models are computer programs that produce meteorological information, including prognostic charts, for future times at given locations and altitudes. ![]() The Aviation Weather Center re-sends these maps, and also generates specialized maps for aviation. Within the United States, these type of maps are generated by the Hydrometeorological Prediction Center, the Storm Prediction Center, the Ocean Prediction Center, and the National Hurricane Center. Manual prognostic charts depict tropical cyclones, turbulence, weather fronts, rain and snow areas, precipitation type and coverage indicators, as well as centers of high and low pressure. For purposes of severe weather, prognostic charts can be issued to depict current weather watches, convective outlooks for thunderstorms multiple days into the future, and fire weather outlooks. Prognostic charts can be made of isentropic surfaces (along a certain potential temperature surface determined in kelvins) in regards to moisture advection, mean temperatures at the surface, mean sea level pressures, and precipitation either for a single day or multiple days. They show areas where visual flight rules are in effect, instrument flight rules are in effect, the height of the freezing level, the location of weather features, and areas of moderate to severe turbulence. Low-level prognostic charts used by aviators show the forecast between the Earth's surface and 24,000 feet (7,300 m) above sea level over the next two days. Wave prognostic charts show the expected sea state at some future time. Surface wind direction and speed is also forecast on this type of chart. Surface weather prognostic charts for mariners indicate the positions of high and low pressure areas, as well as frontal zones, up to five days into the future. Prognostic charts generated by computer models are sometimes referred to as machine-made forecasts. The forecast map showing the state of the atmosphere at a future time is called a prognostic chart. ![]()
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