Wind slab remains the primary concern, with the chance of loose wet avalanche activity diminishing. Wind and precipitation are forecasted to ease over the next 24 hours. The chance of an uncontrolled slide will increase if a wet snowpack locks up with an overnight refreeze. 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. The new snow has been transported by gale-force winds over the past 24 hours. Sheltered terrain features such as rocky catchments near ridgelines are the locations where wind slab deposits will develop. Any loaded start zone lacking support will be an area of concern and should be treated with caution.
A loose wet avalanche problem exists as rain breaks down surface structure at lower elevations. Steep slopes will become prone to triggering if freezing levels remain elevated with rain. The freezing level is forecasted to lower, which will reduce the chance of loose wet avalanche activity.
No avalanche activity has been reported or observed over the past 24 hours. The current weather conditions have limited observations.
At Whakapapa, on average, 8 cm of new snow has accumulated at 2000 metres elevation. This may increase over the next 24 hours. This new snow is now overlaying the widespread rime crust. In the south, this rime crust also exists but only on exposed slopes which is also being covered by new snow accumulation. Facet weakness and graupel layer were observed recently. A warming spike this afternoon is making surface conditions wet. 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, but this is also changing fast. Recent snowfalls have improved snow cover overall and lowered the threshold elevation in the northern and eastern areas (about 1600 metres elevation).
Monday the 10th of August will have a few showers, sleety about the tops. The winds are strong north-westerly, tending westerly throughout the day. The freezing level is about 1800 metres elevation. A low and associated front passes over the country today, then sits just to the east of the country by the end of the day. Tomorrow, the low and associated front continue to move east as a thin ridge of high pressure moves onto 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.
Low
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
