Regimes of Widspread Heavy Precipitation in Diverse Geographic Regions

This study considers MERRA2 (Modern-Era Retrospective analysis for Research and Applications Version 2), which is explored to determine the large-scale conditions associated with episodes of widespread heavy precipitation. This study focuses on a region centered on western Nebraska, as well as the country of Argentina. These regions are chosen as a proof of concept region (where the statistics of heavy precipitation are reasonably well known) and to explore the variability of rainfall in the domain of the upcoming RELAMPAGO field project respectively. A widespread heavy precipitation event is considered to have occurred when 24hr precipitation at a MERRA2 gridpoint (resolution 0.5 degrees latitude by 0.625 degrees longitude) exceeds the 99.9^th percentile of the series of running 24hr sums of precipitation at that location for the period 1980 – 2016. Heavy precipitation often occurs on the convective scale, but the resolution of the analyzed dataset is too course to resolve these scales, and instead resolves precipitation affecting broader area. Yet when heavy precipitation occurs on these broader scales, it often poses a threat for larger-scale flooding. These events are then analyzed with PCA (Principal Component Analysis) to objectively identify the atmospheric patterns leading to these events. Using the first PCA at each gridpoint composites are made to illustrate the most common regimes of widespread heavy precipitation at these gridpoints. Analysis of these patterns reveals that it is not always necessary to have top-end precipitable water present for top-end precipitation, if enough synoptic-scale lift is present. Furthermore, knowledge of the preferred Argentinian patterns will help aid forecasters during the upcoming RELAMPAGO field project.