Wind slab will develop on south- and east-facing slopes over the next 24 hours. Cornice formation is likely as the new snow starts to be transported. The storm system will affect the region over the next few days, bringing snow and poor visibility. Winds will be severe gale at times. Managing a developing avalanche hazard with these types of conditions will be difficult. Recommend delaying any alpine travel until conditions improve.
Wind slabs will form. New snowfall accumulation will provide loose material for transport. Any new or old loose snow will be transported to south- and east-facing slopes above 1600 metres. Sheltered terrain features such as rocky catchments near ridgelines will also have wind slab deposits. Freshly loaded start zones lacking support will be areas of concern and should be treated with caution.
Cornice formation will likely occur as winds start to transport the new snow. Cornice formations will be isolated to south- and east-facing ridgelines. Cornices will be touchy to light loads throughout the storm cycle. 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.
Tuesday 28th July was an active day with human-triggered and natural avalanche activity in the backcountry. Winds loaded north- and west-facing slopes during the day. Multiple size-1 avalanches were reported, but one natural event is estimated at size 2 near the crater. Check the photo taken on the 28th of this size 2 natural avalanche. This is a north-facing slope at an elevation of about 2550 metres.
Currently, winds are moving snow around with some loading occurring. Early afternoon today, the 30th, snowfall has started, which will compound the wind slab problem. The northern areas have been going through a melt-freeze cycle at the lower elevations. On average, the last storm cycle brought half a metre of new snow to the region at an elevation of 2000 metres. The older, deeper snowpack is consolidated and supportive. Snow cover exists on Mt Ngauruhoe and Mt Tongariro. If doing the Tongariro crossing, you will be traveling over snow and ice. Alpine gear and precautions need to be considered. The south-west areas have enough snow cover in start zones above 1600 metres for avalanches to run freely (threshold). In the northern areas, the threshold is at a slightly higher elevation, but this is also changing fast. This last snowfall has improved snow cover overall and lowered the threshold elevation in the northern areas and east (about 1600 metres elevation).
Tomorrow, the 31st of July, will have heavy rain easing to showers before dawn. Snow lowering to 1200 metres in the afternoon. The winds are strong to gale north-westerly, severe gale at the higher elevations. The freezing level is 1800 metres, lowering to 1400 metres Friday afternoon. A front moves northwards over the South Island today. Tomorrow, the front continues moving east across the North Island, followed by cold southerlies brought on by a complex trough moving onto the South Island.
Slick rime crusts are present, posing a sliding hazard. Strong to gale winds are stripping any loose snow, exposing these crusts on ridgelines and windward terrain features. 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)
