Assessment of Alaska rain-on-snow events using dynamical downscaling

The ice formed by cold season rainfall or rain-on-snow (ROS) has striking impacts on the economy and ecology of Alaska. An understanding of the atmospheric drivers of ROS events is required to better predict them and plan for environmental change. The spatially/temporally sparse network of stations in Alaska makes studying such events challenging and gridded reanalysis or remote sensing products are necessary to fill the gaps. Recently developed dynamically downscaled climate data provide a new suite of high-resolution variables for investigating historical and projected ROS events across all of Alaska from 1979-2100. The dynamically downscaled ERA-Interim reanalysis replicated the seasonal patterns of ROS events but tended to produce more rain events than in station observations. However, dynamical downscaling reduced the bias toward more rain events in the coarse reanalysis. ROS occurred most frequently over southwest and southern coastal regions. Extreme events with the heaviest rainfall generally coincided with anomalous high pressure centered to the south/southeast of the locations receiving the event and warm air advection from the resulting southwesterly wind flow. ROS events were projected to increase in frequency overall and for extremes across most of the region but were expected to decline over southwest/southern Alaska. Increases in frequency were projected due to more frequent winter rainfall but the number of ROS events may ultimately decline in some areas due to temperatures rising above the freezing threshold. These projected changes in ROS can significantly affect wildlife, vegetation and human activities across the Alaska landscape.


Bieniek, P., Bhatt, U.S., Walsh, J.E., Lader, R., Griffith, B. Roach, J. K., Thoman R. L.. 2018. Assessment of Alaska rain-on-snow events using dynamical downscaling. American Meteorological Society. 57: 1847-1863. DOI: