Tongariro

Wind slab development is possible when the new snow gets transported by winds. Snowfall accumulation will be enough for slab formation on slopes with terrain catchments. The weather remains changeable over the next 24 hours; snow showers are possible with strong winds, gale at times. Poor visibility is expected, making navigation and hazard management difficult.

No natural or human-triggered avalanche activity has been reported over the past 24 hours.

In southern areas over the past 48 hours, moderate to strong easterly winds have transported loose snow onto westerly-facing slopes. Some wind-scouring on exposed slopes has occurred. At the lower elevations, a rime crust has formed overnight, making for slick off-trail conditions on all aspects and elevations; old deeper snowpack is consolidated and supportive. In the northwestern areas near Whakapapa, a facet crust combination weakness has been noted. Questions remain on distribution and reactivity once stressed by subsequent loading. Yesterday, graupel was noted at 2000 metres elevation, buried and as a surface form. 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 1500 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 recent snowfall has improved snow cover overall and lowered the threshold elevation in the northern and eastern areas (about 1600 metres elevation).

Tomorrow, Tuesday the 4th of August, will have showers, some heavy with snow to 1300 metres, becoming isolated in the morning but remaining cloudy. The winds at 2000 metres will be strong to gale force, becoming southerly severe gale in the evening. The freezing level lowers to 1100 metres overnight, lowering again to 500 metres in the afternoon. A ridge over the North Island is displaced today as a cold front in the far south moves northeast across the South Island, followed by cold southwesterlies. The front reaches central New Zealand late tonight, then moves across the North Island tomorrow while high pressure builds over the South Island.

Slick rime crusts exist. Recently, a new rime crust has formed. During the last storm, gale winds stripped ridgelines and windward terrain features, exposing hard icy crusts. 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.

Low

• We are uncertain due to a limited number of field observations.
• We are uncertain about forecast snowfall amounts.