Surface hoar observations at the scale of a helicopter skiing operation

Abstract

Understanding what controls coarse scale snowpack properties, such as surface hoar distribution, is imperative for predicting snow avalanches. Due in part to the inherent difficulties of winter travel in mountainous terrain, most spatial variability investigations of snow properties have been limited to relatively fine scales. To quantify snow surface spatial variability at the basin, region, and mountain range scales, a team of heli-skiing guides recorded observations describing surface hoar presence or absence coordinates, crystal size, and elevation throughout four major surface hoar formation periods over two heli-skiing seasons in rugged alpine terrain near Haines, Alaska across an extent of nearly 60 km. Geostatistical analysis yielded spherical semivariogram autocorrelation ranges from approximately 3-25 km, which is similar in size to many of the basins and regions within the study area. Kriging models built from the semivariograms were produced to aid geographic visualization of coarse scale snowpack processes. Geographically Weighted Regression revealed a positive relationship between elevation and surface hoar crystal size with adjusted R 2 values averaging near 0.40. The results of this research suggest it may be possible to identify areas with greater surface hoar growth and persistence potentials as a consequence of synoptic onshore or offshore flow, and glacially influenced katabatic winds. Additionally, larger surface hoar crystals may be found in the higher elevation avalanche starting zones in the alpine glaciated terrain near Haines, Alaska. These results can help in future efforts to forecast snow stability patterns over large areas.