CrossOverTemperatureIndex

Fog Forecast Based on Cross Over Temperature Index

The Cross Over Temperature (COT) is a practical meteorological indicator used to assess the likelihood of fog formation, particularly during nighttime and early-morning hours under stable atmospheric conditions. It represents the approximate temperature at which the air becomes saturated when cooling occurs at nearly constant moisture content. Fog is more likely when the forecast minimum temperature approaches or falls below the calculated COT. The difference between the forecast minimum temperature and COT provides an indication of fog potential: a small positive difference suggests increasing probability of fog, while temperatures at or below COT indicate a high likelihood of saturation and fog formation. The index is especially useful for operational fog forecasting over airports, road networks, agricultural areas, and other weather-sensitive activities. However, fog development also depends on wind speed, cloud cover, terrain, moisture availability, and boundary-layer stability.