Ensemble Tool

The Ensemble Tool is designed to create new display fields from gridded ensemble datasets (mean, min, max, median, range, sum, and standard deviation) and to facilitate cycling through multiple model family displays. There are two important tabs. The Legends tab and the Matrix tab.

Legends Tab

The GFS Ensemble Forecast System (GEFS) is the primary ensemble dataset available in AWIPS for use with the Ensemble Tool at WFOs. The AWIPS GEFS dataset contains a 21-member ensemble of surface temperature and precipitation, as well as a 12-member ensemble of Mean Sea-Level Pressure, max temperature, min temperature, and a wide variety of fields (height, temperature, relative humidity, and wind) at standard pressure levels (1000mb, 925mb, 850mb, 700mb, 500mb, and 250mb).

To use the Ensemble Tool to create new derived field displays, the user first loads the tool from the Tools menu and then uses the Volume Browser to load a parameter in the ensemble dataset. Each member loads as a separate color that can be toggled on or off, and the user clicks the gear button to choose what field will be calculated for the visible members toggled on. For example, to compute the minimum value at each point among all the members, the user selects Min. The minimum value is then computed and added as a contoured image in the display. Derived fields cannot be converted to images, however. The derived fields do allow for specific contour control that is unique to this tool.

The Ensemble Tool also allows for sampling of all the fields in the display, and it also contains a distribution viewer (also accessible from the gear menu) for creating probability density function/cumulative density function graphs. After loading the distribution viewer, as the user samples the display, the distribution graph of all the members updates for the location of the mouse pointer.

In the distribution graph, each ensemble member value is indicated by a red tic mark on the x axis. The range of data is broken up into bins and the number of values in the bins is plotted along with the cumulative percentage at and below the values. This can be particularly useful in diagnosing different solution modes, say for when half the members have large precip and half have none and an average value can be misleading. 

Matrix Tab

The Matrix tab of the Ensemble Tool allows the user to load groups of model family parameters available from the Volume menu and rapidly cycle through the different models. The are different model family presets that can be selected from the initial menu upon clicking on the Matrix tab, each tailored for use in different meteorological scenarios (winter, severe weather, etc.). While you can combine different models in a four panel display, the Matrix tab within the Ensemble Tool is a more dynamic and relatively easy way to load and cycle through multiple models at different times. In 17.3.1, the Matrix tab will have problems that will be fixed in 18.1.1.

The Ensemble Tool will not be used in RAC, but if you would like to learn more about it, see the Ensemble Tool VLab reference page with job sheets.