Fog Forecast Based on Fog Stability Index

The Fog Stability Index (FSI) is a diagnostic parameter used to estimate the atmospheric conditions favourable for the development and persistence of fog, particularly during the night and early morning. It combines near-surface temperature, humidity, wind and atmospheric stability characteristics to indicate the likelihood of fog formation. Lower FSI values generally represent a more stable, moist and weakly ventilated boundary layer, which is favourable for radiational fog formation. Higher values indicate greater atmospheric mixing and less favourable conditions for fog. The index is useful for operational forecasting at airports, highways, urban areas and other weather-sensitive locations. FSI should preferably be interpreted together with surface dew-point depression, wind speed, cloud cover, soil moisture and boundary-layer conditions, since fog formation is influenced by several interacting processes.

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