Climate simulations have projected an increase in extreme precipitation during the winter months in much of the United States, so it is important to focus on how to simulate better these events. For instance, crop fields may be washed away due to flooding and extreme snowfall events, causing revenue loss by stakeholders. One way to understand better the simulation of these extreme precipitation events in climate models is to assess the sensitivity to model resolution. Winter months are ideal for analysis as the dynamics of weather systems producing extreme precipitation have scales that regional climate models, in particular, can resolve the synoptic scales.

This study focuses on the Upper Mississippi River Valley during the months of December, January, and February (DJF). We analyze six-hourly precipitation covering 2002-2012 to evaluate the effectiveness of the RegCM4 and WRF regional climate models in replicating Stage IV observational extreme precipitation at various resolutions. We also evaluate 2-m temperature, 2-m specific humidity, 500 hPa geopotential heights, and 10-m winds to assess the physical conditions leading to extreme precipitation events. The 700 hPa vertical motion, 2-m temperature gradients, 2-m moisture gradients, and 10-m wind convergence are also analyzed to examine various aspects of frontal strength and rising motion.

As resolution increases the WRF model tends to replicate better the observational behavior compared to RegCM4, especially for extreme precipitation. WRF produces stronger temperature gradients, horizontal convergence, and vertical motions during extreme events. WRF also produces substantially more convective precipitation during the extreme events, which may be linked to the strong vertical motions. The outcome is strong extreme precipitation that agrees better with observations.