Wind slab formation is possible due to increasing winds with snowfall. A loose-wet problem may also develop at the lower elevations. The weather will deteriorate over the next 24 hours. Winds will become strong at times, and visibility will be poor. Managing alpine hazards will become challenging.
Wind slabs will develop on southern aspects above 2000 metres over the next 24 hours. Once the new snow starts to get moved around, wind slab deposits will form near sheltering terrain features and catchments. Triggering will be possible on steep start zones lacking support. The loose snow available for transport will be low volume, but even 5cm of new snow can equate to a 15cm slab once transported.
Loose wet avalanche activity will become possible over the next 24 hours. Rain will reduce the structural integrity of the surface layer. Any steep slope lacking support will become prone to loose wet avalanche activity. Visibility will be poor at the higher elevations, hindering slope assessment and navigation. Signs of a developing surface instability are roller ball and point release below cliff bands. Monitor foot penetration and precipitation.
No natural or human-triggered avalanche activity has been reported or observed over the past 24 hours.
Surface snow was partially saturated by rain during the last storm cycle. Snowpack has now moved into a melt- freeze cycle. Surface deposits (crusts) are now providing structure to the snowpack. No significant weaknesses currently exist; however, some isolated facet layers have been noted on shady aspects. An overnight refreeze of the surface snow occurred, locking up the snowpack, creating a consolidated mass. Snow cover exists on Mt Ngauruhoe and Mt Tongariro. 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. Threshold elevation is about 1600 metres.
Thursday the 13th of August will have rain for a time in the morning and afternoon, falling as snow to 2100 metres; otherwise cloudy with isolated showers. The wind is a strong northeasterly, possibly easing in the afternoon. The freezing level is at about 2400 metres. A front moves eastwards onto the country today, followed by a broad trough. The trough continues to cover most of New Zealand tomorrow, while a low approaches the upper North Island from the Tasman Sea.
Increasing winds will strip exposed slopes, leaving the surface slick and icy. 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)
