During approach, low clouds can obscure a pilot's view of the runway until the aircraft descends below the cloud ceiling. Low ceilings therefore drastically shorten the time window within which pilots conduct the final and most crucial landing procedures. Because of the dangerous conditions that low ceilings create, air traffic to effected airports is often limited via the activation of IFR constraints and reduced landing and takeoff rates. Planners for airport operations and flight scheduling use cloud ceiling forecasts to try to anticipate air traffic restrictions. Accurate cloud ceiling forecasts translate into "business as usual" operations, missed forecasts can create one of two problems. When the forecast calls for adequate cloud ceilings and low cloud ceilings occur, the impact on aviation operations can be classified as "chaotic". Associated with this scenario are decreases in safety, delay impacts to passengers and clients, and severe financial impacts to airlines and airports. Inversely, when the forecast calls for low cloud ceilings and adequate ceilings occur, airport resources become under utilized due to planning for limited air traffic. Although this scenario does not pose a safety threat, the financial impacts can be significant.
A major part of the problem is the reliance on a single forecast. A better approach would be to provide separate forecasts, each with an associated likelihood, of the most significant cloud ceiling possibilities. Ensemble forecasting is one possible method for providing such forecasts. Ensemble forecasting consists of generating and comparing several distinct forecasts that are valid for the same time and as such these forecasts afford a view of the range of possible weather outcomes. To derive meaningful values of probability, the forecasts are statistically scored then compared via cluster analysis. This paper presents a probabilistic cloud ceiling forecasting technique based on ensembles of NWP models and the results from employing this technique to produce probabilistic cloud ceiling forecasts for Logan International Airport in Boston MA for a one month period.
The 8th Conference on Aviation, Range, and Aerospace Meteorology