An active northerly storm system is moving into the forecast area with winds up to severe gale strength. Periods of heavy rain and snow accompany this system. Prior to the storm there was already large amounts of loose dry snow available for transport. These factors will combine to create a period of potentially intense avalanche activity. Avalanche terrain should be avoided at higher elevations today and any back country travel considered carefully.
The combination of periods of heavy snowfall and severe gale force winds from the N 1/4 plus existing large amounts of loose dry snow available for transport will likely create a widespread windslab hazard. Slopes lee to the NW will be of particular concern but unstable pockets may exist on specific terrain features on all aspects.
With gale force winds from the NW 1/4 last night wind slab avalanches would have most likely occurred given the large amounts of loose dry snow available for transport . Previously, widespread size 1-2 natural wet avalanches were observed over the past two days on steeper solar aspects as the days warmed. A small slab was triggered by a climber on a steep south facing slope at 2100m - a reminder that specific terrain features can produce small avalanches.
If you see any recent avalanche occurrences or have any relevant snowpack information or photos, you can share them via the Public Observations link on the NZAA home page.
Approximately 10cm of new snow fell above 1700m on Friday and a further 10-30 cm on Saturday. This snow has generally well bonded to the old snow surface falling with little wind. This loose dry snow will have been re-distributed by overnight winds and there is likely to be areas of wind pressed and wind scoured snow.
Before this, on 1st - 4th of August, very strong winds from the west and south have significantly stripped any exposed faces and features; other downwind areas in the lee have been left with variable surface conditions and multiple layers of very dense hard slab ranging from 10-60cm thick. This slab now appears very stubborn and unreactive. Large cornices have also formed above 1800m.
The snowpack remains relatively shallow for the time of year. Approximately 60- 70 cm below 1700m and 120cm at 2000m. Crevasses are still very open, and many rock features are still visible, particularly on west-facing aspects.
Although the lower part of the snowpack also appears consolidated and unreactive, the Aspiring region is very large, and there is still limited data. Caution should still be taken, particularly in steeper, more extreme terrain where unknown weaknesses may exist.
Periods of heavy rain developing in the morning, with snow to 1500 metres.
Wind at 1000 metres: Northeasterly gale 75 km/h, rising to severe gale 100 km/h for a time in the morning and afternoon.
Wind at 2000 metres: Northerly gale 75 km/h, rising severe gale 120 km/h for a time in the morning and afternoon.
Wind at 3000 metres: Northerly gale 70 km/h, rising to severe gale 120 km/h for a time in the morning and afternoon.
Freezing level: 1500 metres, lifting to 2000 metres in the afternoon.
Exposed areas such as ridgelines on west and south aspects may have been stripped back to old ice layers by strong winds. Depending on your objective, an ice axe and crampons could be necessary.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
