Synoptic Climatology of Rain-on-Snow Events in Alaska

Abstract

Rain-on-snow (ROS) events can have adverse impacts on high-latitude ungulate populations when rain freezes in the snowpack, forming ice layers that block access to winter forage. In extreme cases, ROS events have led to mass die-offs. ROS events are linked to advection of warm and moist air, associated with extratropical cyclones. However, these conditions are common to many winter precipitation events, challenging our understanding of the particular conditions under which ROS events occur. This study uses the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) to differentiate ROS events in Alaska from precipitation events in which only snow falls on a preexisting snowpack [snow-on-snow (SOS)]. Over the North Slope and Kotzebue Sound, no clear difference exists between the tracks of ROS-producing and SOS-producing storms. However, in the interior, southwest, and Anchorage, tracks of ROS-producing storms tend to be farther north and west than for SOS-producing storms. The northwest shift of ROS-producing storms is linked to the position of upper-tropospheric anticyclones in the eastern Gulf of Alaska during ROS events. ROS-producing storms are no more intense than SOS-producing storms, but their association with atmospheric blocking leads to stronger pressure gradients on the east side of storms and thereby stronger advection of positive anomalies in temperature and precipitable water. For several sites, sea level pressure in the eastern Gulf of Alaska is also significantly higher a few days prior to ROS events than prior to SOS events, further implicating atmospheric blocking as a facilitator and potential predictor of ROS events.

Identification of Seasonal Streamflow Regimes and Streamflow Drivers for Daily and Peak Flows in Alaska

“…Rain‐on‐snow (ROS) events, in which streamflow is generated by snowmelt and rainfall, occur across Alaska, most commonly in the western Interior and South Coastal regions (Bieniek et al., 2018; Pan et al., 2018) and most frequently October–April (Bieniek et al., 2018). ARs combined with ROS events (Crawford et al., 2020; Guan et al., 2016) can lead to substantial flooding (McCabe et al., 2007). Outside South Coastal, precipitation falls mainly in summer–mid fall in the form of frontal systems and convective storms, with convective storms especially common in the Interior in June and July (Farukh et al., 2011; Papineau & Holloway, 2011; Shulski & Wendler, 2007).…”

An assessment of Southern Hemisphere extra-tropical cyclones in ERA5 using WindSat

“…The cyclone tracking algorithm used in this study was detailed by Crawford and Serreze (2016) and has subsequently been used in a number of further studies (e.g., Koyama et al, 2017;Crawford & Serreze, 2017;Crawford et al, 2020;Hell et al, 2020). The algorithm uses sea level pressure information rather than 850 hPa vorticity.…”

An Assessment of Southern Hemisphere Extratropical Cyclones in ERA5 Using WindSat

“…The cyclone tracking algorithm used in this study was detailed by Crawford and Serreze (2016) and has subsequently been used in a number of further studies (e.g., Crawford & Serreze, 2017; Crawford et al., 2020; Hell et al., 2020; Koyama et al., 2017). The algorithm uses sea level pressure information rather than 850 hPa vorticity.…”