Observed Climatological Relationships of Extreme Daily Precipitation Events With Precipitable Water and Vertical Velocity in the Contiguous United States

Abstract

An analysis of 3,104 stations in the United States shows virtually every station exhibits a positive correlation between precipitable water (PW) and extreme daily precipitation (EP) with over one-third statistically significant. To first approximation, EP scales linearly with PW, but there is nonlinear scaling at the lower and upper ends of the PW distribution. On average, EP is amplified by twice the amount of PW, but there is substantial seasonal and spatial variability caused by dynamically forced vertical velocity with stations ranging from a one-to-one relationship to over three-to-one. These latter stations are generally found in elevated terrain or near coasts and in regions and seasons affected by strong synoptic-scale weather systems. The results also point to PW, not vertical velocity, as the key limiting factor in the most intense EP events. This has important implications for projecting changes of the most intense EP events in a warmer world.