Wind slabs exist on northern and west-facing slopes. These wind-driven deposits are showing signs of strengthening. Today the weather has improved, but strong to gale winds are to persist over the next 24 hours, with poor visibility and snow showers returning. Managing avalanche hazards in poor visibility is difficult. Recommend delaying alpine travel until you can see and identify the hazards.
Wind slabs have formed by strong to gale winds transporting the new loose snow. Any future snowfall accumulation will be deposited on west- and north-facing slopes. Wind slab deposits will form near sheltering terrain features and catchments. Triggering will be likely on steep start zones lacking support. If you do venture out, recommend a cautious approach to any freshly loaded slope, especially convex-shaped, high in the path.
Cornice development around ridgelines facing north or west has occurred. The new snow will continue to be transported by persistent winds over the next 24 hours. Cornice is continuing to develop in isolated locations. Failure will be possible once weight exceeds support, triggering wind slab on the slope below. Recommend avoidance and maintaining a decent distance even after the storm event.
Multiple avalanches of size 1 were initiated by Whakapapa ski patrol today. Locations were at about 2100 metres elevation on north-facing aspects.
Overnight, new snow accumulation at Turoa was about 15- 30 cm above 1600 metres elevation. Wind slab deposits up to 100 cm in depth above 2000 metres elevation exist in the southern areas on northern and west-facing aspects. These wind slabs have shown signs of strengthening. Typically, new snow weaknesses form within these deposits during development, with the new-old snow interface a potential bed surface. In the northwest of the area near Whakapapa, a refreeze occurred due to the lower freezing levels. In the northwest, isolated pockets of wind slab exist. Very little new snow has accumulated in the northwest, but snow transport has occurred. The gale southerly winds have stripped exposed slopes, leaving a rain crust at the surface. Threshold is now about 1800 metres in the northwestern areas. In the south-west area, the older snowpack was saturated by rain a few days ago, now refrozen and supportive. Even after recent rain, snow cover will still exist on Mt Ngauruhoe and Mt Tongariro. Sub-zero temperatures currently; snow and ice are present on the Tongariro Alpine Crossing. Alpine skills and equipment are essential to hike this track. If doing the Tongariro Crossing, you will be traveling over snow and ice with exposure to start zones at threshold. Recommend alpine gear and take avalanche precautions. Threshold in the southwest remains at an elevation of about 1600 metres.
Tuesday the 18th of August will have a few showers developing in the morning. Snow will lower to 800 metres in the evening, affecting the Desert Road. The winds are strong southerlies, rising to gale force later in the day. The freezing level is 900 metres, rising over the next 24 hours to 1100 metres elevation. A showery south-to-southwest flow affects the country today and starts to weaken tomorrow as an area of high pressure approaches New Zealand from the west.
Strong winds will strip exposed slopes, making the surfaces slick and icy. Numerous hazards, including exposed rocks and cliff bands, exist. It is recommended to carry an ice axe and crampons when venturing into the backcountry. Having strong alpine skills and competence is essential for navigating over slick surfaces, as the consequences can be severe.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
