Effect of Mesoscale SSTs on Atmospheric Rivers and Heavy Rain Along the West Coast of North America at Subseasonal Time Scales

Atmospheric rivers (ARs), which are long and narrow plums of intense water vapor transport, have been recognized as one of the most important sources of extreme hydroclimate events in global extratropics, capable of producing torrential rains and floods when making landfall over regions of elevated orography, such as the West Coast of North America. Numerical weather prediction (NWP) models still suffer significant defficiencies in predicting landfalling ARs, pointing to the need of understanding the cause of model errors and improving models’ forecast skills. By conducting a large ensemble experiment with a high-resolution regional climate model, we provide evident that mesoscale SSTs associated with oceanic fronts and eddies can modulate the occurrence frequency, intensity and position of landfalling ARs at subseasonal time scales. As such, heavy rainfall over the high mountainous terrain along the west coast of America are significantly affected by the mesoscale SST forcing. These results provide a new perspective on AR dynamics, which potentially can lead to new improvements for predicting ARs and associated extreme rain events at subseasonal time scales.