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Forecast Model Gridpoint (GRIB) Contouring

The forecast model gridpoint data contouring program is grbcalc. This program reads in and decodes GRIB data, derives the appropriate variables and contours the grid. The gridpoint data are saved in large data files that contain all the possible gridded fields for a particular model runtime. Since all grids are grouped together, three pieces of information must be specified in order to determine which grid to contour. First, the user must select the forecast time.  Time selections range from the initialized fields to out to ten day forecasts depending on the forecast model. The second selection involves the choice of a vertical level. These gridded data are placed on mandatory levels but also include tropopause and maximum wind level data. In addition, there are some sounding and surface level data provided for those variables. The third piece of required information is the variable or parameter. There are standard variables in which the gridded fields are broadcast as part of a model's data stream. These variables include temperature, geopotential height, U and V wind components, and relative humidity. From these variables several derived variables may be generated. The variable selection closely resembles the upcalc program. As mentioned above several sounding variables such as sea level pressure, quantitative precipitation, stability variables and thickness are provided. Since not all models will have all times, levels and variables available, it is recommended to view the available grids using the griblook program.  When these three pieces of information have been specified, the program searches for the appropriate grids needed to generate the requested output. Additional computations are performed and the output grid or grids are then contoured. Once a variable has been derived, the gridded field may be saved in a gridded file for later use.

NOTE: WXP can display GRIB files directly from sites such as NOAA/NCEP/NIC. There is no need to process these grids with the WXP ingestor. Grbcalc and contour can display these grids but cannot compute derived grids unless all grids for the computation are in the same file. Thus, it is recommended to download multigrid files. If the downloaded file contains only one grid, it should be combined (concatenated) with other similar grids into one coherent GRIB file.

grbcalc -cu=la -mo=eta -ft=h24 -le=850 -va=temp -in=2 -pl=cf 
  -ct=rainbow.clr -cof=0-23 -de=d -cb=-20
grbcalc.gif (24538 bytes)

For further information about WXP, email technical-support@weather.unisys.com
Last updated by Dan Vietor on June 6, 1998