Tongariro

Wind slabs continue to form on northern and western aspects, mostly in southern areas of the region. The weather is forecasted to improve over the next 24 hours, but snow showers and strong to gale winds are likely to persist overnight into Wednesday. Winds will ease with visibility improving as high pressure moves into the region. Managing avalanche hazards in poor visibility is difficult. Recommend delaying alpine travel until you can see and identify the hazards.

Multiple avalanches up to size 1.5 were initiated by Whakapapa ski patrol yesterday, 17082026. Locations were at about 2100 metres elevation on north-facing aspects.

Over the past 72 hours, Turoa has received about 30-40 cm of accumulated storm snow above 1600 metres elevation. This new snow was paired with gale southerly or southeast winds. Wind slab deposits are up to 100 cm deep in the southern areas on northern- and west-facing aspects. During testing yesterday, these wind slab deposits had shown signs of strengthening. But 24 hours is a long time in the alpine, and one thing is certain: change is constant. Typically, new-snow weaknesses form within these deposits during development, with the new-old snow interface serving as a potential bed surface. In the northwest, isolated pockets of wind slab exist. Very little new snow has accumulated in the northwest, but snow transport has occurred, and wind-driven deposits have developed. The gale southerly winds continue to strip exposed slopes, leaving a rain crust at the surface. Threshold is now about 1800 metres in the northwestern areas. Snow cover will 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.

Wednesday the 19th of August will be cloudy with snow showers, mainly about the southern slopes, fine spells elsewhere. The winds will remain gale to strong southerlies overnight, easing around midday Wednesday. The freezing level is 1100 metres, lowering to 1000 metres over the next 24 hours. A showery south to southwest flow weakens during today and tomorrow as an area of high pressure slowly pushes onto Aotearoa New Zealand from the west.

Strong winds can 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

• We are confident the likelihood of avalanches will increase with the forecast weather.
• We are uncertain due to a limited number of field observations.