• Weather accounts for 70 percent of all delays in the national airspace, with convective weather accounting for 60 percent of all weather delays (see Figure 1–1).

  • Convective weather is difficult to forecast.

  • Traffic flow managers need 2 to 6 hours of lead time for effective planning.

Mr. Washington identified the two different timescales for forecasts in air traffic management. Tactical planning relies on forecasts in the 0- to 2-hour time frame. With improved observational capabilities and data assimilation techniques, the forecast skill for this timescale has improved substantially in the past few years, especially for the 0- to 1-hour range. Strategic planning relies on forecasts 2 to 6 hours into the future. The skill for convective weather forecasting in this timescale is very low, though improvements have been made with the advent of the CCFP.

FIGURE 1–1. Cumulative causes of flight delays per 100,000 activities from 1992 to 2002.

Many workshop participants thought that the 5- to 10-year goals for forecast accuracy set by the FAA in preparation for this workshop (desired false alarm rate (FAR) =0.20, desired probability of detection (POD) =0.80, maximal FAR of 0.30, minimal POD of 0.60) were unrealistic based on current forecasting abilities. Thus, Mr. Washington identified the following



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