Widespread, dense fog can be both hazardous and disrupt commercial transport. Such fog events in the central U.S. were initially examined in the early and mid-1900’s. During the last few decades, radiation fog and coastal advection fog events have been extensively studied in other regions, but not in the central U.S. Early studies suggested that dense and widespread fogs of the central U.S. were largely related to fronts. More recently, however, fogs have been primarily associated with advection of warm moist air over cold or snowy surfaces or with radiational cooling. The purpose of this study is to document the synoptic and surface conditions associated with of fogs of this region.

The environmental conditions associated with dense fog events that occurred at Peoria, IL for the period 1948-1996 will be presented. This study is based on hourly surface observations from approximately 50 sites of horizontal visibility, winds, temperature, humidity and prevailing weather, and also on regional observations of daily snow depth and rainfall. The synoptic setting for fog events has been examined for a subset of the fog events, for those occurring during the 25-year sub-period (1970-1994) primarily employing 3-hr surface charts. The fog events have been categorized by the duration of the event in an attempt to discern the conditions that are most relevant for long-lasting dense events.