The Fire Weather Index (FWI) has been studied by several researchers for a number of geographical areas in the world and has been proven to be an effective index for fire danger assessment. However, limited work has been done so far, for the calculation, the appropriate classification and mapping of FWI, at a higher spatial resolution that could be more efficient for operational use, at both national and local levels, for those countries with similar climatic and physical characteristics to Greece. A methodology is introduced in this paper for a straight-forward calculation, appropriate classification and mapping of the FWI in Greece. The methodology uses the Weather Research and Forecasting (WRF) mesoscale model to obtain high spatial resolution meteorological fields, while at the same time, the proposed classification takes into consideration the environmental variety of the country, which could highly influence the significance of FWI values and consequently their interpretation as reasonable and functional fire danger classes. The proposed approach of Percentile Indices provides suitably varying FWI boundaries of classes based on the specific physical characteristics of the study area. The new methodology of fire danger mapping has been validated using historical datasets of fire ignition location and burned areas of the country during the five-year fire period of study (2009-2013).