Wind slabs and cornice formations at the higher elevations are the primary avalanche hazards. The region is being impacted by a storm, resulting in a rapidly changing dynamic snowpack. Multiple hazards may exist over the next 24 hours. Possible refreeze with surface becoming icy and dangerous, resulting in a sliding hazard.
Wind slab formation has occurred. Locations are on south and east aspects at the higher elevations. Wind slab deposits are likely to form near sheltering terrain features and catchments. Triggering these wind slabs is more likely on steep, unsupported slopes. It's advisable to approach any freshly loaded slope with caution, especially those that are convex-shaped and positioned high in the path.
Cornice formation has most likely occurred. This new snow has been transported, forming a cornice near south- and east-facing ridgelines. Failure will be possible once weight exceeds support. Natural triggers are continued precipitation load. The weight of a single person will also create a failure. Cornice fall is an effective natural trigger for any wind slab on the slope below. Recommend avoidance and maintaining a decent distance even after the storm event.
Loose wet avalanche problem may develop as cooling winds ease and the possibility of the sun making an appearance. Solar aspects, mostly north-facing, will be prone to structural breakdown of surface layers. Watch for signs of solar effect such as rollerball and pinwheel activity. Gauge foot or ski penetration as you travel. Weather forecasts are conflicting, and rain may be the driving force of surface structural breakdown.
No natural or human-triggered avalanche activity has been reported or observed over the previous 24 hours. Current weather conditions have been restricting observations.
Overnight into this morning, 20 mm of precipitation (mostly rain) has affected the snowpack at Turoa below 1900 metres. This has most likely fallen as snow at the higher elevations, with deposits forming on south and east aspects. Current weather conditions are limiting observations above 2000 metres. The deeper supportive snowpack is currently consolidated with no significant weaknesses identified but is heading isothermal at the lower elevations. Around Whakapapa, 3 cm of new snow has been recorded this morning at 2000 metres elevation. This new snow came in wet and overlies the isolated wind slab. A very wet and warm storm system is bringing a mix of precipitation types. Over the next 24 hours, the snowpack may do its classic Ruapehu thing and refreeze, locking up. If this occurs, a robust crust at the surface may become the primary hazard. Threshold is now about 1800 metres in the northwestern areas. Snow cover will exist on Mt Ngauruhoe and Mt Tongariro. 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. The threshold in the southwestern areas remains at an elevation of about 1600 metres.
Monday the 24th of August will be partly cloudy with isolated showers, clearing to fine in the morning. The winds are southwesterlies, gale easing in the morning. The freezing level is about 1600 metres, lifting to 2200 metres in the afternoon. A front moves north of the North Island today, while the South Island is covered by an unsettled westerly to south-westerly flow. Tomorrow, the west-to-southwest flow over southern and central New Zealand eases and turns northwest, while a ridge builds over the north.
A possible overnight refreeze of the wet surface snow will result in a slick crust, increasing the chance of a sliding accident. 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.
Low
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
