Regions
Northwest Inland.
The weather over the few days will deliver an interesting mix of winter and spring-like conditions. Solar radiation may continue to wreak havoc on Monday, so make sure your travel plans allow for changing conditions.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Monday
Weather Forecast
10-15cm of new snow is expected between Sunday night and Monday morning. On Monday, expect mainly cloudy skies, light snowfall and the odd sunny break. Moderate mixed rain and snow (up to 15mm each day) is forecast for Tuesday and Wednesday. Ridgetop winds should be strong from the southwest on Monday, and the become extreme and southwesterly on Tuesday and Wednesday. Freezing levels will yo-yo from 1500m on Sunday night to about 1200m by Monday afternoon and Tuesday morning. From there, the freezing level will gradually spike to about 1800m by Wednesday evening.
Avalanche Summary
Over the past week, loose wet avalanches, cornice failures, and deeper persistent slab avalanches to size 3 were observed failing naturally in response to warming and solar radiation. With snow and wind expected throughout the forecast period, we are shifting back to a general pattern of storm slab avalanche activity. That said, spring-like loose wet avalanches, isolated persistent slab avalanches and cornice failures will still be possible at elevations where precipitation falls as rain or during periods of warming and solar radiation.
Snowpack Summary
By Monday morning, 5-15 cm of new snow is expected to overlie a widespread melt-freeze crust. Below about 1300m, light rain is expected to further saturate the snowpack keeping the snow loose and unconsolidated. The warm temperatures and sun over the last week woke up deeply buried weak layers within the snowpack. This includes a weak crust/surface hoar layer which was buried down 20-30cm in the north of the region, a widespread crust/facet layer buried in early February down up to 1m, a lingering surface hoar layer from January down around a meter, and weak basal facets at the bottom of the snowpack. Cooling should dramatically limit the reactivity of these old layers; however, they may come back to life during future periods of warming, heavy rain or solar radiation.
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.
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.