The snow and wind have arrived. Carefully assess for wind slabs in steep terrain below ridges.
Make conservative travel plans, and seek low-angled / low-consequence terrain as both the new snow and strong winds have created new and reactive wind slabs.
Wind slabs have formed in lee terrain features from all the recent snow. Assess for slabs prior to committing to large terrain. Also use caution in steep wind-sheltered terrain, where the recent snow may take a bit of time to bond to an underlying crust.
On Thursday, Numerous avalanches on the north island in both the alpine and at treeline were observed with a few large (size 2), with most being small (size 1). One large (size 2) natural storm slab avalanche occurrence was observed and reported. Located on north aspect terrain between 1300 and 1400 m elevation, this avalanche was estimated at 15 cm deep and 60 meters wide, running 30 meters in length.
A small (size 1) skier trigger avalanche was reported. This avalanche occurrence was located mid-island on a southwest aspect at 1300 m and was just below the ridgetop. This small slab was estimated at 45cm deep and did not harm or bury the rider.
As new snow and strong winds will continue Friday night into Saturday afternoon, expect both an increase in the available mass for potentially larger avalanches. The additional load could make wind slabs increasingly sensitive becoming more reactive to rider triggering.
It also remains possible that riders could trigger storm slabs in sheltered areas, particularly if all the recent storm snow has a poor bond to the underlying melt-freeze crust.
The upper snowpack consists of 30 to 60 cm of storm snow that has had some time to slowly settle. This overlies a pronounced melt-freeze crust that can be found at elevations 1500 m and below. Above 1500 m the melt-freeze crust begins to lose strength and is less than 1 cm thick.
Snowpack depths are highly variable and have been recorded between 200 and 300 cm, the consistent theme is that they taper quickly with elevation. Although the snowpack in most forested areas below treeline remains below threshold depths. Expect at these elevations terrain that lacks tree coverage such as steep cliffs, and open alpine-like features to have the potential to produce avalanches.
Around 5 to 15 cm of snow is forecast to accumulate by Friday afternoon along with southwest wind. This snow builds on the 30 to 60 cm of snow that accumulated Tuesday night with strong wind. W
Friday Night
Cloudy with snowfall, accumulation 2 to 5 cm, Southerwestern winds 20 km/h strengthening to 70 km/h, treeline temperature 0 °C, freezing level rising to 1500 m.
Saturday
Cloudy with snowfall, accumulation 20 to 40 cm, Southwestern winds 80 km/h easing to 30 km/h, treeline temperature 0 °C. freezing level 800 m.
SundayA mix of sun and cloud, no precipitation is forecast, Northwestern winds 60 km/h to 80 km/h, treeline temperature -7 °C. freezing level 800 m.
Monday.Cloudy with light snowfall, accumulation 2 to 4 cm, Northwestern winds 50 km/h to 80 km/h, treeline temperature -7 °C. freezing level 800 m.
More details can be found in the Mountain Weather Forecast.
