As part of the Fog Remote Sensing and Modeling (FRAM) project (Gultepe et al. 2006), a set of graphs has been made which displays the seasonal-diurnal climatology of fog, visibility and related weather variables at 198 Canadian airports, based on records of hourly observations made during the period from 1971 to 2005 (National Climate Archive 2003). Conditional frequencies of observed variables are graphed as fields along two axes: time of day horizontally (hour UTC) and time of year vertically (month). Frequencies are also plotted for additional conditions such as wind direction, precipitation, cloud, and persistence (Martin 1972). Field values refer to probabilities of discrete weather events and to statistics of continuous weather variables. Additional weather variables described include: cloud ceiling, blowing snow, snow, ice pellets, freezing rain, freezing drizzle, rain, drizzle, temperature, relative humidity, wind speed, and clouds. The results revealed interesting patterns in diurnal and seasonal variation of visibility. In the marine environment, in Atlantic Canada, the maximum probability of fog is about 35% and is likely mostly due to warm air advection (sea fog). Inland, in Ontario, the maximum probability of fog is about 10% and its occurrence is likely due to a combination of advection and precipitation effects related to frontal systems and radiative cooling. Farther inland, in the Prairies, the maximum probability of fog is about 5% and is likely mostly due to radiative cooling. It is concluded that the patterns found were both site-specific and regionally coherent.
Supplementary website: http://collaboration.cmc.ec.gc.ca/science/arma/climatology