Synoptic evolution of Midwestern US Extreme dew point events

Eight Midwestern extremely high dew point events were examined with respect to their synoptic characteristics and evolution. Individual and composite analyses of events suggest that there exists three predominant features associated with extreme dew point events. In nearly all cases, the evolution of the synoptic environment includes the development and propagation of low pressure from the high plains through the upper Great Lakes. The low pressure increases and backs the surface winds acting to advect low-level moisture from eastern Nebraska, Iowa, Missouri eastward into Illinois and Indiana. The progression of the low pressure and attendant frontal boundaries also acts to modulate the length of the extreme low-level dew point event. Healthy crops and sufficient soil moisture content throughout this large agricultural region were also evident during the periods of extreme low-level moisture. Finally, the vertical thermal profile of the atmosphere during extreme dew point events supports previous findings and highlights the importance of restricted low-level mixing as instrumental in allowing near-surface moisture to become trapped and increased. Copyright (C) 2007 Royal Meteorological Society.