Evaluating Forecasts for Navigational Contrail Avoidance

Navigational avoidance as a contrail mitigation strategy has the potential to reduce the climate impact of aviation by as much as half. The effective implementation of avoidance strategies requires forecasts of the state of the upper troposphere and lower stratosphere that are stable (consistent across a range of lead times) and accurate (true to reality). However, the optimal criteria for evaluating whether a contrail forecasting system is sufficiently stable and accurate remain unclear. Here, we argue that forecast stability is best evaluated holistically by asking whether estimated decreases in contrail warming, for a given set of flight trajectories and deviations, are consistent across forecasts with different lead times. We use real-world flight trajectories taken from operational ADS-B datasets and deviations generated using aircraft performance models with a contrail-aware trajectory optimization routine to evaluate the stability of contrail predictions based on ECMWF IFS HRES forecasts. We find a high degree of stability with contrail warming reduced by over 80% even with lead times as long as 48 hours, sufficient to enable pre-tactical contrail avoidance at the flight planning stage. Finally, we show that we obtain large reductions in contrail warming despite frequent pointwise differences in the locations of ice supersaturated regions across forecast cycles because forecasts agree on the broad regions where ice supersaturation occurs.