Exporting an Esri Grid Ascii file

Load or generate a Raster data set into a Map window
Find the Raster data set you want to customize in the Layers list and select it.
Right click it and select Export to Esri Grid Ascii
Specify the location and name of the ASC file you'd like to save and click OK.
A .ASC file will be saved. These files can be loaded by SimClim, ArcGIS, QGIS and many other programs.