Abstract
Cold fronts are typically associated with cooling, drying and a strengthening wind that shifts to have a northerly component. Cold front effects at a particular point, however, are dependent upon pre-existing air mass characteristics. Here, we examine 634 passages of synoptic-scale cold fronts in northeastern Minnesota from 2010 to 2018. While these fronts are associated with the expected effects in some areas, they are often associated with warming and enhanced drying in the region directly influenced by an air mass from Lake Superior (coastal sites). Coastal sites experience warming during more than half of cold frontal passages, in contrast to proximate inland sites out of the influence of the lake. This warming, combined with a removal of the moist lake air mass, often leads to a sharp post-front decrease in relative humidity. These relatively unusual local effects indicate a need to carefully consider characteristics of the lake air mass and likely changes during cold frontal passage when forecasting regional temperature and fire weather conditions.
Highlights
IntroductionCold fronts are baroclinic boundaries, typically strongest at the surface, which, upon passage, are typically associated with cool and dry air advection, and a wind that shifts to have an equatorward component [1]
The Great Lakes are a dominant geographical feature of North America and represent the first major change in land surface conditions as surface weather features sweep south and east across the continent from the Arctic
The focus is on the North Shore of Lake Superior, with inland sites used as a control, since this is the first portion of the Great Lakes region to be affected by cold fronts moving from the north and west
Summary
Cold fronts are baroclinic boundaries, typically strongest at the surface, which, upon passage, are typically associated with cool and dry air advection, and a wind that shifts to have an equatorward component [1]. The air mass which enters behind many cold fronts forms over a cold, dry surface. Prior studies have not identified the typical effects of cold fronts on sensible weather conditions around Lake Superior. It is the broad goal of this study to assess sensible cold front effects near Lake Superior, with a special focus on coastal areas dominated by the marine boundary layer. The focus is on the North Shore of Lake Superior, with inland sites used as a control, since this is the first portion of the Great Lakes region to be affected by cold fronts moving from the north and west
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