Precipitation is "average annual", and is expressed in terms of millimeters (mm.) per year; Average Days of Precipitation ("Wet Days") is number of days per year; and Average Windspeed is expressed in terms of meters per second (note that this is not maximum windspeed, nor is there any directional content included in this data set). It is GRID's assumption that the definition of a "wet day" is one in which enough precipitation occurred on a given day so as to be recordable by a gauging station at a particular location.