The program sfmap plots any parameters which can be derived from the data in a GEMPAK surface data file. These are the program defaults and allow us to list and plot data immediately when starting to use GEMPAK. The X window will display surface observations from ‘Hurricane Bob’ in 1991, centered around West Virginia. GAREA is the graphics area: the part of the map that will be plotted. AREA is the data area: the area from which to select the data to plot. These areas exist separately for when you might want individual control over both the region of the map that is plotted (GAREA) and the region that is covered by data (AREA). If you want to plot a map with complete data coverage, including the edges, you should make AREA bigger than GAREA. This can be done by adding a minus – to AREA or a plus + to GAREA: MAKE NOTE GAREA can be specified in some of the same ways as AREA, with one caveat: You can not use the @ symbol to specify GAREA. Because GAREA defines the boundaries of the graph, adding @ would force an irregular boundary. Think of the @ sign as a way to restrict the selection of data. GEMPAK can also calculate a number of parameters if the requested parameter is not present in the data set, for example, such as with relative humidity, which GEMPAK determines from a function defined internally as RELH=FUNC (TMPC,DWPT). List, for all times in the file, useful for when you don`t know the times when the data was collected: If DEVICE = xw you should see an animation through all times in the file. If DEVICE = gif you’ll see stations plotted multiple times to the map if CLEAR = no is defined. CLEAR is a logical variable which determines whether the graphics screen is cleared before plotting. With CLEAR = n, you have the ability to overlay observations, images, maps and various vector and scalar quantities, depending on the GEMPAK program being used. Additionally, because GEMPAK mapping programs operate within one gplt process (until gpend is called from the command line), you can overlay fields on the same map projection using multiple programs! PROJ determines the map projection, and directly affects the way the map looks on the screen. PROJ and GAREA together give you the flexibility to generate very specific map projections. Both simple map projections and full map projections are avaiable to select: For full map projections, each definition MUST be followed by three specified angles based on the projection class (CYL,AZM, CON), which are defined like so: Display the visible satellite image from 18Z and overlay the surface data for the area covered by the image. Plot a standard station model for each location in the data set. The surface data to plot include: COLORS, MAP, TITLE, FILTER and TEXT control the graphic colors, line thickness, style, text fonts and titles. These map aesthetics allow you to generate very specific graphics. Check the parameter definition pages in the manual for more detail, or with the phelp command at the GEMPAK prompt. Save your session! In the sfmap command prompt, you can save the current definitions with the command You can reload this file in any other GEMPAK program, at any time, to retrieve the saved definitions, though only the variables which were saved in sfmap will be reloaded: Now let’s look at data from today. Using an alias for real-time metar observations SFFILE = metar, and DATTIM = 1200, we can redisplay the map for this morning. But how to know the latest available? Exit SFMAP and return to the terminal, and execute the command line program sfctime metar and you will see surface reports in today’s GEMPAK surface file for every twenty minutes: To overlay the current GOES satellite visible image on your map, you must explicitly define SATFIL. To find the latest EAST-CONUS visible satellite image, list the contents of $SAT/EAST-CONUS/1km/VIS/ with the command: Source.