Ahead of the Round 4 strategic noise mapping under the END, TII commissioned a research project to determine the meteorological correction factors required for CNOSSOS-EU road and railway traffic noise calculationsacross Ireland. Methodologies for determining the percentage favourable propagation were identified under NMPB2008 and NORD2000, and the input data requirements of the methods assessed. Meteo data available from Met Eireann and TII weather stations was collected and collated and compared with the requirements of the two methodologies. The data available in from Irish met stations led to the selection of the methodologyfrom NORD2000 being selected. Thirty years of hourly data was analysed for 26 counties to provide long term weather data for temperature, relative humidity, mean sea level pressure, and percentage of favourable propagation suitable for calculations under CNOSSOS-EU.This paper will present an overview of the methodology, available data and results obtained.