Taftools: Development of Objective TAF guidance at CMC

Terminal aviation forecasts (TAFs) are site-specific forecasts that are currently prepared every 6h manually, using guidance from the operational numerical weather prediction (NWP) models and available observations. TAFs include forecast information on ceiling, visibility, weather, obstructions to visibility and wind. It is believed that gains in forecast production efficiency can be realised by automating as much of the production process as possible, leaving the final control of the forecast contents with the operational forecaster. We use statistical methods because they are cheap compared to other solutions. There are three major components of the project, one for very-short range forecasts, one for the short range and finally, one that will blend the two techniques together and possibly incorporate other available information.

Numerical weather prediction models have difficulties forecasting precise weather elements for a specific site as needed for a TAF. Persistence, especially conditional climatology, is in fact very difficult to beat during the first few hours. It has been shown that a system based on observations is superior to persistence climatology and to NWP-based statistical systems. To take advantage of these results, we are developing a very short-term forecasting technique based solely on current available observations. We will use about 40 years of hourly observations to develop forecast equations relating observations at a time To to observations at a later time To+dT. The equations will be developed using a Multiple Discriminant Analysis (MDA) technique. MDA has recently been shown to give superior forecasts to CART for cloud amount. Most of the work so far has been devoted to the construction of a large database consisting mainly of hourly observations but some results will be shown.

Observation-based systems may provide the best possible forecast at very-short ranges but their skills degrade rapidly in time. It was decided to develop a perfect-prog system to forecast the different elements required to write a TAF. Reanalyses from the National Centre for Environmental Prediction are used to derive site-specific predictors such as temperature, vorticity, moisture advection, stability indices, etc. The predictors are paired with observations which have been processed to be representative of a time-step of 3h. Equations will also be develop using a MDA technique. The presentation will describe the technique design and results to date.

The third component of the project which will blend the two techniques together, and possibly incorporate other available information, is still in its early development stage.