The brunt of the complex storm system has passed with another weaker front crossing the park early on the 29th.
Increasing gale force winds will build new windslab. Frozen surfaces and crusts will increase sliding hazard.
The Hazard remains High on or near the main Divide but Considerable in the East.Take a very slow and cautious approach to any travel in the alpine.
A weaker frontal system crosses the park on the 29th bringing some new snow and further building windslab. Avoid all areas of suspect stiff snow especially close to steep or convex ridgeline entries, unsupported slopes or cross loaded features.
Loose Wet avalanching remains a possibility at lower elevations.Be cautious if you find yourself in a unsupportive and isothermic snowpack especially in steep or unsupported terrain.
28th August. As the storm has cleared we have gained observations on multiple large Loose Wet and Wet slab activity that has run to valley floor on a range of aspectsWet Slab activity to size 3 was also reported from Plateau Hut. Clearing skies also allowed for observations from Plateau hut of multiple Loose Wet avalanches to size 2.5 on the Malte Brun range 27th August - Haszard range - some observations of Loose wet avalanching during the afternoon on various aspects at 2000m and below. A brief break in the weather allowed for observations of Wet slab avalanches on East Aspects around 1100m. Poor visibility hindered any other observations
26th August - Large Loose wet avalanche reported running to valley floor on Mt Ollivier Fan below Mueller Ridgeline reaching the lower bush line. Further observations restricted by current storm cycle.
The 7 day rain total in Mt cook village sits at 373mm. This precipitation has come in as both rain and snow with highly fluctuating freezing levels. We suspect that the snowpack below 2000m may have become isothermic but we are uncertain of the full extent of how far the rain has penetrated the snowpack. Throughout the day on the 28th of August the Freezing level has been sitting close to 2100m. With freezing levels lowering to 1400m overnight on the 28th of august there could be a wide spread Melt freeze Crust that caps the isothermic snow below.The head of the Tasman Glacier may have received over 5m of snow which will have been re-distributed by Gale to severe gale force North East winds to Mod Easterly winds and then back to Severe gale force North Westerly winds on the 28th. Gale force NW winds will continue through the Saturday the 29th. This means there will be a highly variable snowpack surface from stiff windslab on lee aspects, wind stripped on windward aspects and a Melt freeze crust possibly everywhere below 2000m. Any new snow will be falling on a range of different surfaces and crusts with suspect poor bonding.
The snowpack will now need a full re-assessment when the weather allows
Showers, more persistent in the evening. Snow to 1100 metres.
Wind at 1000 metres
Northwesterly gale 70 km/h.
Wind at 2000 metres
Northwesterly gale 70 km/h.
Wind at 3000 metres
Northwesterly severe gale 90 km/h, easing to gale 70 km/h for a time in the morning and afternoon.
Freezing level
1400 metres, rising to 1700 metres in the evening.
Forecast Gale force Northerlies will strip exposed ridgelines. Ice axe and crampons advised if you must travel
Low
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
