Abstract
ABSTRACTFor 175 difficult-to-forecast persistent deep slab avalanches, weather data were obtained from Global Environmental Multiscale (GEM) models produced by Environment Canada. The focus was to determine critical parameters and thresholds for avalanche forecasting from GEM and compare them with weather station data analyzed in Part I (Conlan and Jamieson, this issue). The high-resolution GEM-limited-area model (2.5 km resolution) forecasted higher median precipitation amounts than both the lower-resolution GEM15 (15 km resolution) and weather stations within a small dataset. Air temperatures were lower for both weather models compared with the weather station data, likely because of elevation differences. A multivariate classification tree created with GEM15 data correctly classified 29 of 36 avalanches by their primary cause-of-release, using a primary split of modelled solar warming of 5.9°C, 10 cm into the snowpack. For all 175 avalanches, GEM15 forecasted significantly less precipitation than observed at the weather stations, particularly with multi-day cumulative amounts. The majority of GEM15 surface wind speeds were between 0 and 10 km h−1, producing negligible wind loading amounts. The parameter values may be helpful for predicting future persistent deep slab avalanches. However, GEM output is not always representative of field conditions and should be used in conjunction with other sources.
Highlights
The release of naturally triggered persistent deep slab avalanches, subsequently called avalanches, occurs due to the influence of certain weather parameters on the snowpack
Days and locations of persistent deep slab avalanches that released naturally in western Canada and that were difficult-to-forecast were obtained for our study
We identified some advantages of using GEM15 and Global Environmental Multiscale (GEM)-limited-area model (LAM) data
Summary
The release of naturally triggered persistent deep slab avalanches, subsequently called avalanches, occurs due to the influence of certain weather parameters on the snowpack. They often release from overburden loading from snowfall or wind-transported snow that increases stress intensities and strain rates. They release due to elevated strain rates caused by warming of the upper snowpack because of strong shortwave radiation (solar) or warm air temperatures. To forecast such events, weather monitoring is important for avalanche professionals and outdoor activities. We assess the advantages and limitations of weather models for forecasting naturally triggered deep slab avalanches
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