Meteorologists use many tools to predict the weather. They use past data such as temperature observations, real-time data such as radar and satellite images, and models that look into the future. Many different parameters are plotted using the numerical forecast models, which are generated using computers. The models consist of numerical equations which use current conditions as the inputs. The resulting outputs are forecasts for what is likely to happen in the future, based on those initial conditions. There are many different models that all attempt to do the same thing.
The Flow Following Finite Volume Icosahedral Model (FIM) was developed by NOAA to produce weather forecasts and is unique because it uses an icosahedral grid rather than a grid of the latitude and longitude lines like most weather models. The icosahedral grid is mostly hexagons except for 12 pentagons (think of a soccer ball).
Seven different datasets have been created using the real-time output from FIM. All of them have either mean sea level pressure (MSLP) contours or 500mb height contours. The 500mb height is the height at which the pressure is 500mb. When the 500mb height is low, there is low pressure at the surface, and when the 500mb height is high, there is high pressure at the surface. Patterns of troughs and ridges which play a huge part in the weather can also be seen clearly on the 500mb height plots. The 500mb height is also an indicator of atmospheric temperature. The 500mb heights as an image is available with MSLP or 500mb height contours overlaid (1 and 2). This allows viewers to see the relationship between 500mb heights and surface pressure. The precipitable water image is available with the MSLP or 500mb height contours (3 and 4). Precipitable water is the amount of water that can be obtained from the surface to the "top" of the atmosphere if all of the water and water vapor were condensed to a liquid phase. This differs from the precipitation image, which shows the amount of precipitation that is expected in six hour increments (5). This image is available with mean sea level pressure contours overlaid. Most of the precipitation that falls is associated with areas of low pressure. The 500mb height contours are also overlaid on an image of the 500mb wind speeds (6). The areas of highest wind speeds are the jet stream. The final dataset that is available is an image of 850mb temperatures with mean sea level pressure contours overlaid (7). 850mb is just above the surface. All of these datasets go out to 240 hours and are shown in one hour time steps (though technically they are time interpolated from 6-hourly gridded data.) The exception to this is the precipication dataset which has six hour increments. Model updates are available every 12 hours.