Loose wet avalanche problem may develop on solar aspects throughout Tuesday, the 25th of August. Wind slabs are lingering and gaining strength. The weather is settled over the next 36 hours, but isolated showers are a possibility.
A loose, wet avalanche problem may develop as cooling winds ease, with sunny periods possible. Solar aspects, mostly north-facing, will be prone to structural breakdown of surface layers. Watch for signs of solar effect such as rollerball and pinwheel activity. Gauge foot or ski penetration as you travel.
Wind slabs exist but are gaining strength and are stubborn to trigger, becoming unreactive. Locations are on south and east aspects at the higher elevations. Wind slab deposits will also be near sheltered terrain features and catchments. Triggering these wind slabs is more likely on steep, extreme, unsupported slopes.
No natural or human avalanche activity has been reported or observed over the past 24 hours.
Over the past 24 hours, about 6 mm of precipitation (rain) has impacted the snowpack, with 1 cm of new snow recorded at Turoa at 2000 metres elevation. Whakapapa received about 5 cm of new wet snow accumulation at 2000 metres elevation. This came in with elevated temperatures assisting the bonding process. The deeper supportive snowpack is currently consolidated with no significant weaknesses identified, but is heading isothermal at the lower elevations. This was a very wet and warm storm system that brought a mix of precipitation types. Over the past 24 hours, the snowpack has done its classic Ruapehu thing, refreezing and locking up. Threshold is now about 1800 metres in the northwestern areas. Snow cover will exist on Mt Ngauruhoe and Mt Tongariro. Snow and ice are present on the Tongariro Alpine Crossing. Alpine skills and equipment are essential to hike this track. If doing the Tongariro Crossing, you will be traveling over snow and ice with exposure to start zones at threshold. Recommend alpine gear and take avalanche precautions. The threshold in the southwestern areas is at an elevation of about 1700 metres.
Tuesday the 25th of August will have cloudy periods with the odd shower. The winds are moderate westerlies. The freezing level is 1900 metres, lifting to 2400 metres over the next 24 hours. A west to southwest flow over southern and central New Zealand eases and turns northwest, while a ridge of high pressure builds over northern New Zealand. Tomorrow, the high over northern North Island slowly moves eastwards while a front moves onto the South Island.
An overnight refreeze is possible, resulting in a slick crust. This will increase the chance of a sliding accident. Strong winds can strip exposed slopes, making the surfaces slick and icy. Numerous hazards, including exposed rocks and cliff bands, exist. It is recommended to carry an ice axe and crampons when venturing into the backcountry. Having strong alpine skills and competence is essential for navigating over slick surfaces, as the consequences can be severe.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
