PNNL

Abstract

Hurricane Helene was deadly and destructive, with orographically driven precipitation in the Appalachians contributing to historical rainfall and flooding. Here, we quantify the orographic effects on precipitation from Hurricane Helene by performing a novel set of simulations of the storm with and without the topography of the Appalachians using the Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM). We found that the Appalachians led to over four times more upslope rainfall, which was driven by enhanced vertical motion in the simulation with topography. The pathways for precipitation formation, however, are similar for both simulations. Cloud condensate primarily forms from vapor to liquid water condensation, and accretion is the main mechanism for rain formation. The effects of orography enhance these mechanisms, with higher precipitation efficiency in the simulation with topography indicating that the mountains lead to a more efficient storm with respect to converting available moisture into surface rainfall.