EXPLORING THE POTENTIAL FOR REAL-TIME FORECASTING OF LOW-VISIBILITY EVENTS AT ACTRIS RADO–BUCHAREST FACILITY, ROMANIA

F. Toanca¹, A. V. Dandocsi^1,2, A. Ilie^1,3, J. G. Vasilescu¹, D. N. Nicolae¹, A. Nemuc¹, R. Pirloaga¹

¹National Institute of Research and Development for Optoelectronics, INOE, Măgurele-Bucharest, Romania, ²UNST Politehnica of Bucharest, Bulevardul Iuliu Maniu 1-3, Bucharest, 061071, Bucharest, Romania, ³Faculty of Geography, University of Bucharest, Bulevardul Nicolae Bălcescu 1, 010041, Bucharest, Romania

Low-visibility events (LVEs), such as fog and haze, significantly affect transportation, safety, and public health. We present a real-time forecasting system for LVEs at the ACTRIS RADO–Bucharest facility, integrating a microwave radiometer (RPG-HATPRO G5), a ceilometer (Lufft CHM15k), and surface air quality measurements (PM2.5, PM10, NOx). LVEs were defined as horizontal visibility below 1 km, detected by surface sensors and verified via ceilometer backscatter. Thresholds for fog preconditioning were derived from 53 episodes (Oct 2021–Mar 2023), including relative humidity RH >65% in the lowest 100 m, total cloud cover TCC >6 oktas with >50% cloud fraction between 0–1000 m, and vertical optical range VOR <1000 m. One hour before onset, RH exceeded 80% in 38 cases, TCC reached 7–8 oktas in ~50% of episodes, and VOR ranged 100–2000 m. At fog initiation, 96% of cases showed TCC = 9 oktas and VOR dropped to 140–240 m, confirming nearly saturated, aerosol-rich conditions. The system successfully generates timely alerts, potentially supporting operational LVE forecasting.