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Numerical Forecasting Models
Numerical forecasting models provide guidance in forecasting many weather parameters, including pressure fields, humidity, clouds, winds, temperatures, precipitation, and sea heights.Models forecast at scales including global, synoptic, and regional. They fall into two general categories: those based on statistical data concerning frequency of occurrence
(i.e., of thunderstorms, tropical storms, tracks and intensities) and those based
on hydrodynamic equations of the behavior of the atmosphere.These "dynamic" models rely on input data that can be from observations (ship observations, station
observations, bouy data, radiosonde data, etc.) or from the outputs of other models. Different dynamic models represent the atmosphere at different levels of resolution in terms of horizontal scale or grid size (i.e., 9 kilometer, 27 kilometer) and the number of vertical layers of the atmosphere across which the calculations run. Models also differ in
their temporal range (i.e., short-range,. medium-range, and long-range). Models differ in that some take terrain (elevation) into account. Some models also accept data on sea surface
temperatures. The run of a dynamic model begins with a process called initialization in which the parameters must be set for the initial conditions in each cell and for the conditions at the boundary of the model's areal extent. For example, the output from a global model can be used to specify the conditions of the atmosphere at the boundary for a regional model. The initial conditions for the cells within the region would be initialized on the basis of observational data. After initialization, the model runs the hydrodynamic equations iteratively across intervals (e.g., 6 hours, 12 hours, 36 hours, etc.). All models have biases and tendencies--things they tend to forecast well, things they do not, things
they tend to under-forecast, things they tend to over-forecast, etc.
Models that are widely used in the weather forecasting
community include:
The Aviation Run (AVN) of the National Center for
Environmental Prediction's Medium-Range Forecasting Model
Naval Ocenaographic Global Atmospheric System (NOGAPS)
The Global Model run by the United Kingdom Meteorology
Office (UKMET)
The model run by the Geophysical Fluid Dynamics
Laboratory (GFDL)
The Climatology and Persistence (CLIPER) statistical
model of hurricane track forecasting run by the National Hurricane Center,
A variety of web pages describe models and their tendencies
in detail.
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