Wind slabs are lingering mostly on south aspects. Wet snowpack may lock up with an overnight freeze. The chance of an uncontrolled slide will increase. A slick, icy surface can be lethal. Recommend a considered assessment of the surface conditions before committing to an ascent.
Wind slabs have formed on mostly south aspects and are gaining strength rapidly. Sheltered terrain features, such as rocky catchments near ridgelines, are where wind slab deposits will remain. Any loaded start zone that is steep and lacks support will be an area of concern and should be treated with caution. Even though gaining strength at certain locations, triggering will remain a possibility.
No avalanche activity has been reported or observed over the past 24 hours. Above 2000 metres elevation, observations have been limited by the poor visibility and weather conditions.
Whakapapa and Turoa were affected by similar amounts of precipitation over the past 24 hours. New snow has accumulated at 2000 metres elevation and above but came with gale winds mostly northerly. An estimated new snow total is 10 to 15 cm, with 80cm deposits observed at Turoa at 2300 metres elevation. Warm temperatures and wet new snow have helped minimise new snow instabilities. These wind-driven deposits have good bonding to the old snow surface and are void of any significant weaknesses. Overall, the snowpack is well consolidated. Facet weakness and graupel layer were observed recently. Recent rain and warming spikes have made the snowpack wet but not completely saturated. This type of weather can have a positive effect on snowpack stability, nullifying the preexisting facet weaknesses. An overnight clearing may lock up the snowpack with a freeze, creating a consolidated mass. Snow cover exists on Mt Ngauruhoe and Mt Tongariro. These northern mountains are likely to have wind slabs also. If doing the Tongariro Crossing, you will be traveling over snow and ice with start zones at threshold. Recommend alpine gear and take avalanche precautions. The south-west areas have enough snow cover in start zones above 1500 metres for avalanches to run freely (threshold). In the northern areas, the threshold is at a slightly higher elevation. Threshold elevation in the northern and eastern areas is about 1600 metres.
Tuesday the 11th of August will have a few Isolated showers before dawn, then clearing to fine. Cloud developing in the evening. The winds are moderate westerly, tending more southerly and easing, becoming light. The freezing level is about 2000 metres, lifting to 2500 metres in the morning. A thin ridge moves onto the country today from the west as a low to the east of the South Island drifts northeast. Tomorrow, the ridge slowly shifts east as a broad trough and associated front approaches the country from the west.
If a refreeze occurs overnight, the surface will be very slick and icy. Wind-stripped ridgelines and windward terrain features will have a hard, icy surface. Numerous hazards, such as exposed rocks and cliff bands, remain. Carrying an ice axe and crampons is recommended in the backcountry. It is essential to have strong alpine skills and competence when travelling over slick surfaces with high consequences.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
