A climatological study of low ceiling and fog associated with the occurrence of precipitation in the northeastern United States

A previous study has shown that a significant fraction of fog events in the northeastern United States occur under the influence of precipitation. It is also found that a significant fraction of precipitation events are also associated with low level cloud ceilings. Thus precipitation seems to play a significant role in the formation of low ceiling and visibility (C&V) conditions. Therefore, a more complete description and understanding of the underlying physical processes of the influences leading to the occurrence of such events is desirable. An analysis of the environmental conditions associated with low ceiling and fog events occurring under the influence of precipitation is presented using a 20-year dataset of historical routine surface observations as well as radiosoundings. Relationships between precipitation type and intensity at the onset of fog and low clouds are examined, as well as transitions in precipitation character. Structures of the lower atmosphere associated with low C&V events are examined using available radiosounding data. An analysis of other environmental parameters observed at the time of onset, such as wind speed and direction, temperature and pressure is also presented.