Snow accumulations could be greater in the southern part of the region, potentially resulting in locally higher avalanche danger in the Alpine on Saturday and Sunday.
Confidence
Fair - Track of incoming weather is uncertain on Sunday
Weather Forecast
Synopsis: A frontal system is forecast to move through on Friday night, followed closely by another system on Saturday night. Conditions should begin to dry out later on Sunday and Monday as a brief ridge of high pressure forms. Tonight and Saturday: 10-15 mm of precipitation, easing off in the afternoon. The freezing level is around 1500 m, lowering in the wake of the system. Winds are moderate from the south-southwest. Sunday: Moderate precipitation is possible but confidence on Sunday is low. Some models show the bulk of the precipitation heading south of the border. Temperatures continue to cool slightly. Monday: Drier conditions are likely. The daytime freezing level could rise to 1800 m, especially if the sun makes and appearance.
Avalanche Summary
No new avalanches have been reported in the past couple days. Previous reports from earlier in the week included loose wet sluffs up to size 2 on solar aspects and isolated cornice failures.
Snowpack Summary
New snow may not initially bond well to the previous snow surface, which potentially includes a melt-freeze crust, moist or wet snow, or pockets of surface hoar. Also, expect pockets of wind slab to form in exposed lee terrain in the alpine as winds pick up on Thursday night. The upper snowpack at lower elevations has become isothermal from recent warm temperatures. Adding rain to this on Friday could trigger loose wet sluffs or wet slabs in steep terrain. Cornices are very large and could pop off with continued mild temperatures. A layer of surface hoar (buried on March 11; now down about 60 cm) is still being observed in some locations. Triggering this layer has become unlikely, and would most likely require a large trigger or from a thin snowpack zone. Mid and lower snowpack layers are well bonded.
Problems
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.