Visibility forecast verification at Jomo Kenyatta International Airport
The economic growth of any airline is largely determined by the optimum operationalization of the flight schedules. Bad weather and in particular low visibility at the airport may lead to interruption of the schedule. Low visibility may also lead to delays for several hours when taking off and holding for some time or diversion. Diversions to nearby airport lead to large economic losses to the airline. Visibility forecasts are very critical in flight planning hence considerable interest in assessing its accuracy, skill and value. The visibility forecasts form part of the Terminal Aerodrome Forecast (TAF) provided by aerodrome meteorological office.TAF comprises of forecast for wind speed and direction, visibility, weather and ceiling conditions. In this research the forecasts for visibility was verified against visibility observation for 0hr and 6hr lead times. The lowest observed value was used to score against the lowest forecasted value. Visibility was categorized into ranges of poor covering range between 0-1000m, fair between 2000-4000m and clear between 5000-9999. The entries were then made into a 3-category contingency table for six hour lead time. Accuracy at 0hr and 6hr lead time was evaluated using the scatter plot and the root mean square error for days with determinable visibility both in the forecast and in the observations, visibility of 9999 were dropped since specific visibility value could not be determined. Various skill score were then evaluated from the contingency table. The accuracy and skill scores for visibility forecasts are high for 0hr lead time as compared to 6hr lead time hence the visibility forecasts should be used immediately after production and limited to not more than six hours since its accuracy and skill drops drastically. For flight planning the new and amended forecasts should be treated with urgency since convey more accurate forecasts. The verification results should be able to show the strengths and weaknesses attached on the visibility forecasts thereby acting as a tool to foster further improvement in low visibility forecasting on the part of the forecasters. The skill scores generated from the contingency table will assist the management in advancing ways of improving low visibility forecasting by improving the equipments for observing and forecasting low visibility and also initiating further training in low visibility forecasting for forecasters.