Synoptic and quantitative attributions of the extreme precipitation leading to the August 2016 Louisiana flood

Abstract

The catastrophic August 2016 flood in the U.S. state of Louisiana was a result of intense precipitation produced by a slow-moving tropical low-pressure system interacting with an eastward traveling baroclinic trough to the north. While tropical-midlatitude interactions of this nature are rare, they are not unprecedented. Analyses presented point toward the tendency for more and perhaps stronger upper level troughs propagating out of the western U.S. in summer; these then have an increasing potential to cross paths with low-pressure systems that form around the Gulf Coast. Combined with the projected increase in precipitable water, resulting precipitation magnitude would increase. Large-ensemble modeling indicates that the prospect of future tropical-midlatitude interactions is a scenario that Louisiana will face in the future, while regional simulations estimate that the climate warming since 1985 may have increased the event precipitation (11–14 August 2016) on the order of 20%, all of which allude to a conceivable forecast of nonhurricane-related, warm season extreme precipitation in the Gulf Coast states.