A Verification Procedure for Terminal Aerodrome Forecasts

Terminal Aerodrome Forecasts (TAFs) and long TAFs are issued by forecasters in the Hellenic National Meteorological Service for the upcoming 9 or 24 h respectively, for all airports to aid in flight planning. The most important predicted parameters are wind speed and direction, weather phenomena, and visibility. A verification procedure comparing TAFs to Meteorological Aerodrome Reports (METARs) can be helpful for improving the skills of forecasters. To this end, software was developed to read the raw format structure of TAFs and METARs and compare them. The wind speed and direction for each forecast hour are verified according to thresholds specified by the International Civil Aviation Organization (ICAO), and a summary is produced, showing correct, overestimated, and underestimated percentages. A weather phenomenon, such as rain (RA) or thunderstorm (TSRA), is usually given inside a probability time window in a TAF (e.g., PROB40 TEMPO RA). In such a case, the occurrence or absence of the phenomenon and its frequency inside the time window are considered when determining the forecaster’s skill (correct, false alarm, or miss), evaluated using categorical indices such as POD, ETS, and FAR over a number of TAFs. A similar procedure is carried out for visibility range intervals. In this study, verification was performed for a test period of January 2023 for 14 Greek airports. Results indicate generally good performance in predicting wind speed and direction, and also demonstrate the TAFs accuracy in detecting phenomena like rain, although with a notable tendency for false alarms. A systematic tendency to underestimate actual visibility, especially inside TEMPO statements is observed.