Large windslabs are the main concern in the north of the range where the hazard is Considerable.
If you are heading to the south of the area, watch for signs of warming the hazard in the south is Moderate.
Windslabs have formed at higher elevations. North of Stag Saddle, they are expected to be large.
Reports from the southern end of the range suggest the slabs are smaller, and show a large variation in how easy they are to trigger.
Safe travel on Monday will depend on your ability to assess individual slopes.
Take care to identify any wind loaded terrain and consider the consequences before committing to a slope.
The severe gale westerly wind should decrease the risk of loose wet avalanches on Monday.
However, warm temperatures and a strong sun may rapidly over heat the snowpack during the heat of the day.
Areas where new snow sits on a firm crust will be of particular concern.
Watch for signs of the snowpack heating like roller balling and be prepared to change plans.
Mainly fine with areas of afternoon and evening high cloud.
Wind at 1000 metres
Westerly gale 70 km/h, rising to northwesterly severe gale 90 km/h in the afternoon.
Wind at 2000 metres
Westerly severe gale 90 km/h.
Freezing level
1500 metres, lifting to 2000 metres in the morning and to 2500 metres in the afternoon.
Rain has softened crusts at lower elevations. Higher ground could still have a slick sliding surface . A slip or fall on steep terrain could have serious consequences.
Assess runout zones before committing to steep slopes, and carry equipment appropriate for firm alpine conditions, such as crampons and an ice axe. Conservative route selection remains the most effective way to manage these hazards.
Moderate
No recent avalanche activity has been reported. However, observations have been limited due to the weather.
If you see any activity on the Two Thumb Range, please make a public observation. It helps us to produce accurate forecasts.
Southern end of range — south of Stag Saddle
Only about 10cm of snow fell about Stag Saddle on Sunday, tapering to less than 5cm at the southern end of the range. This was distributed by severe gale westerly winds into small drifts up to 25cm deep.
Ridge-lines and slopes exposed to the south-west winds, are heavily scoured and stripped back to slick crusts and scree on upper ridges.
Multiple crusts exist in the old snow on all elevations and aspects. Facets (sugary crystals) have begun to form around these crusts at upper elevations, but have not posed problems. At mid-lower elevations, the old snow is well settled and consists of mainly melt forms or round crystals.
Snow depth varies from 40-75cm, with deeper accumulations of 100-120cm in sheltered areas.
Northern end of range — north of Stag Saddle
The snowpack North of Stag Saddle is not well understood.
We expect over 30cm of snow has fallen, which will have formed large windslabs in areas sheltered from the westerly wind.
Prior to this storm, we only have one observation from Monday 10th August from the area around Captains Peak and Mt Toby, reporting only slightly more snow than around Camp Stream or the Richmond Range, with very little old avalanche debris observed. A similar snowpack to the South was reported.
Photos are of the snowpack prior to the current storm cycle.
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
