Confidence
Fair - Timing of incoming weather is uncertain
Weather Forecast
A steady stream of weather systems will continue to deliver heavy to very heavy precipitation, strong winds, and fluctuating freezing levels. Tuesday night through Wednesday: Up to 70cm of snow. Very strong SW-W winds. Freezing level (FL) rising to 1600-1800m overnight. Thursday: Snow beginning later in the day; 15-30cm. Moderate to strong SW-SE winds. FL lowering to 1000-1200m. Friday: Drier during the day but could see another system arrive in the evening. FL around 1000-1200m.
Avalanche Summary
Numerous Size 1-2 slab avalanches (both natural and human triggered) have been reported in the past 48 hours, primarily in wind affected terrain near ridge crests. There is one new report of a Size 2 accidentally triggered avalanche in the Spearhead Range on December 26. It was a close call that resulted in some lost skis, but fortunately no full burial or injury. Expect the size and likelihood of avalanches to increase through the forecast period.
Snowpack Summary
Storm snow amounts vary from 25-35cm in the northern part of the region, to around 50cm in the southern part. Wind slabs continue to grow in exposed NW-E facing slopes, probably as deep as 100cm in some areas. A weak rain crust is found below the new snow up to treeline elevations. This crust may sit on top of buried surface hoar and/or facets may persist 10-20cm below. Watch this layer as it gets more load and a thick cohesive slab develops, particularly below treeline where the buried surface hoar would be especially large. A strong mid pack overlies basal facets that have also gained considerable strength. On average the snowpack is around 200cm deep near treeline.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.