Fog Climatology and Stability Index for Plovdiv 1991–2018

Abstract

Fog can cause large economic losses for public services and in particular aviation where the cost of flight delays and rescheduling is estimated to hundreds of millions of euros per year. Despite the continuous improvement of weather prediction fog diagnosis and forecasting remains a challenge. In the US alone, 74% of the fatal car crashes are associated with recorded low visibility but without fog warning in the forecast. Today the operational fog forecasting is mainly done with “in-house” developed tools, which is understandable due to the fog life cycle peculiarity. The aim of this work is to investigate the fog climatology for Plovdiv, Bulgaria, for the period 1991–2018 and to use it for calculation of a threshold value of stability index, which can be implemented as an operational forecast tool. One fog case in January 2013 is selected for numerical weather prediction simulations with the WRF model for the city of Plovdiv. It was found that while the index with its site specific threshold value describes well the fog evolution, the WRF model has large deviations in temperature compared to the observations during daytime.