Tongariro

Wind slabs have formed on the south and east aspects. As the winds shift direction on Saturday, August 1st, expect the loading aspects to change. A storm system will continue to affect the region over the next 24 hours, but snowfall intensity and winds are expected to ease. Managing avalanche hazards under these conditions will be challenging. It is recommended to delay any alpine travel until conditions improve.

A size 1 avalanche triggered during slope assessment yesterday (30072026). This event was controlled by Turoa ski patrol at Mid Munga Gully, southeast aspect, at 1700 metres elevation.

Snowfall and wind have affected the snowpack over the past 24 hours. Currently, winds are moving new snow around, forming wind slab deposits. On average, about 20cm of new snow has accumulated at an elevation of 2000 metres. More intense wind in the southern areas has affected the 24-hour snowfall reading at Turoa’s weather plot. A warming spike this morning has resulted in a brittle rime crust forming over the new snow at 2000 metres. The older, deeper snowpack has been shown to be consolidated and supportive recently. 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 1700 metres elevation).

Tomorrow, Saturday the 1st of August, will have showers, with snow possible above 800 metres, becoming isolated with longer fine breaks in the morning. The winds are strong to moderate north-westerly, tending southerly over the next 24 hours. The freezing level is 1100 metres, lowering to 800 metres in the afternoon. A front moves to the east of the North Island today, followed by a westerly. Meanwhile, a complex trough moves over the South Island today, leaving strong, cold southerlies in its wake. The trough moves over the North Island tomorrow, then a ridge of high pressure builds over the country.

Despite the new snow, slick rime crusts will remain. Gale winds have 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.