Factors Affecting the Inland and Orographic Enhancement of Sea-Effect Snowfall in the Hokuriku Region of Japan

The Hokuriku Region along the west coast of the Japanese island of Honshu receives exceptionally heavy sea-effect snowfall accumulations in the winter months, with season total snowfall accumulations exceeding 500 cm at sites near sea level, and 1500 cm at high-elevation sites. Though the climatological enhancement of snowfall is large, the lowland-upland snowfall distribution within individual storms is highly variable, presenting a challenge to operational forecasting and an opportunity to learn more about the atmospheric processes driving the variability.

Utilizing data from a Japan Meteorological Agency (JMA) C-band surveillance radar, the ERA-Interim reanalysis, and surface precipitation observations from the JMA network for 9 cool seasons (Dec–Feb), we examine the factors affecting inland and orographic enhancement in the Hokuriku region. These factors include the strength of the boundary layer flow, the sea-induced Convective Available Potential Energy (SCAPE), the depth of the Planetary Boundary Layer (PBL), and the location of convergence zones and precipitation shadows generated by upstream terrain features. These results, in combination with recent work in the contrasting geography of the Tug Hill region downstream of Lake Ontario, improve our understanding of the enhancement of lake- and sea-effect snowfall and contribute to the general understanding of terrain influences on precipitation.