Climatological Anaylsis of Synoptic Patterns Conducive to Anomalously High Precipitable Water Along the Colorado Front Range During the North American Monsoon

The North American Monsoon (NAM) is an atmospheric circulation system that develops over the lower latitudes of North America in response to the thermal contrast between the continental land mass and adjacent oceans. This monsoonal circulation supplies a critical amount of the total annual precipitation in the southwestern United States during the summer months of the year. Along the Front Range of Colorado, the NAM is also a significant contributor to annual precipitation, and commonly contributes to severe thunderstorms and flooding hazards. Historically, monsoonal related events have been difficult for forecasters to predict due to, in part, the intra-seasonal variability in available atmospheric moisture. In an attempt to improve forecasting abilities of significant monsoonal events along the Colorado Front Range, this study conducts a climatological analysis of available atmospheric moisture, quantified as the precipitable water (PWAT) recorded by RAOB sounding analyses. These archived PWAT data are initially utilized in this study as a means to determine the average monsoon onset and retreat dates in central Colorado through assessing statistical deviations at relevant sounding sites (i.e. KDRN) from the climatological average. Daily rainfall data recorded at the more spatially-dense surface observation sites are also statistically compared against the climatological mean will also be used to corroborate the PWAT-determined monsoon seasonal bounds. Archived Colorado sounding PWAT data from the past 40 years occurring within this defined monsoon season will be analyzed. All daily PWAT values two positive standard deviations away from climatology will be considered anomalously high. The synoptic environments of all events will be analyzed to identify atmospheric synoptic pattern favorable for these anomalous PWAT values. The effects of the El Niņo Southern Oscillation (ENSO) on PWAT are also considered, as previous studies have shown the resulting sea surface temperature changes during ENSO have a significant effect on moisture content and monsoon anomalies. Thus, any events occurring within an El Niņo or La Niņa year will be separately categorized and compared accordingly to develop additional patterns that may provide clarity on the inter-seasonal differences in available atmospheric moisture during the Colorado monsoon season.