Front Range severe flash flooding and El-Niño

An advance is developed in the ability to forecast flash floods in the Colorado Front Range. Three major flash flood events are compared by examining the similarities of the rain events that produced them and their link to the El-Niño/Southern Oscillation (ENSO). Two of these events occurred in Colorado’s Front Range while the other occurred in the Black Hills of South Dakota. All three occurred during the onset summer of an ENSO warm phase. A comparison of the origin of their mid-tropospheric level moisture supply is done using NCEP data and satellite imagery. This comparison reveals the major source of moisture to be the ENSO-warmed waters of the eastern Pacific. Climatological data show a significant increase in flash flood frequency during the onset summer of an ENSO warm phase over the past decade. Similarly, a study of extreme storms of the type that are capable of producing flash floods shows a much greater frequency of occurrence during ENSO warm phases. Since El-Niño can be forecast with accuracy, considerable advance warning of potential flash floods is possible if one uses the synoptic signatures developed in this study.