Intrastorm Variability of the Inland and Orographic Enhancement of a Sea-Effect Snowstorm in the Hokuriku Region of Japan

A prolonged period of winter monsoonal flow brought heavy sea-effect snowfall to the Hokuriku Region along the west coast of the Japanese island of Honshu from 2–7 February 2010. Snowfall in some locations exceeded 140 cm, but the distribution within the event was highly variable. We examine the factors contributing to these variations using data from a Japan Meteorological Agency (JMA) C-band surveillance radar, JMA soundings, surface precipitation observations, and a Weather Research and Forecasting (WRF) model simulation.

There were three distinct periods during the event. Period 1 featured relatively weak flow with precipitation confined mainly to the coast and lowlands. Precipitation maxima were located where the flow ascended: (1) over terrain-blocked air, (2) at the foot of a high flow-normal barrier, or (3) relatively unimpeded over the lower mountain ranges. Flow strengthened during Period 2, yielding stronger vertical velocities over the terrain with precipitation maxima shifting inland and to higher elevation. The flow strengthened further in Period 3, with the precipitation maxima shifting higher in elevation and into the lee, with almost no precipitation falling in the lowlands. Thus greater inland penetration and enhancement of precipitation occurred as the flow speed increased, but additional factors such as the subcloud sublimation of hydrometeors and the convective instability also contribute to differences between periods 2 and 3.

These results illustrate the importance of incident flow strength in modulating the distribution and enhancement of snowfall in lake- and sea-effect regions, with implications for our general understanding of orographic influences on precipitation.