engleski

Displaying the Verification Results of Terminal Aerodrome Forecasts for Thunderstorms and Visibility

As part of a quality management system, ICAO Annex 3 requires verification of forecasts. Terminal Aerodrome Forecast (TAF) is important in decision making during the flight planning process. Verification procedures are not standardized but one of the leading approaches is proposed by Mahringer (2008). It is based on verifying the best and worst conditions for each hour, between observed and forecast states. Data used for verification are TAF forecasts and observed reports (METAR) which are issued half-hourly. The occurrence of a verified event is rather rare owing to three reasons ; because the forecast is for a given point, the verification time period is just one hour and aviation requirements usually refer to high impact weather. At Croatian airports the occurrence of thunderstorms is about 1-2% in terms of hours yearly, hence thunderstorm can be regarded as a rare event. Therefore, for comparing results the diagram with bias and tetrachoric correlation coefficient (TCC) is used. Together with climatological probability, this triplet fully describes contingency tables (Juras and Pasaric, 2006). Moreover, it is suggested that TCC is a good measure of association of a contingency table for rare events. When verifying visibility, a multi categorical contingency table with class limits arising from criteria for groups of changes in a TAF forecast is calculated. Consequently, instead of TCC, the polychoric correlation coefficient (PCC) is used. Bases on this approach, several applied diag rams which reveal verification results to users are shown.

TAF, verification, airport, thunderstorm, visibility

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