Wind Slabs are more likely in the south and east of the range.
Small avalanches can still have big consequences.
Assess loaded features and runouts.
Wind Slabs will be possible to trigger at upper elevation bands across the northern half. These will fail on firm old snow surfaces, or within new snow.
Look out for smooth, rounded pillows of wind-drifted snow, changes in snow texture and hollow-feeling slabs over firmer old snow.
With the combination of new snow on firm old surfaces, a sunny day, and rising temperatures, small loose wet avalanches will be possible.
Watch for roller-balling and signs that the snow is losing cohesion. Check your runout — cliffs, gullies and exposed rocks can have big consequences.
No new avalanche observations.
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
Up to 20cm of cold southerly snow fell with little to no wind in the south and east of the range over Saturday and Sunday. This tapered to 5cm in the west with stronger winds, and isolated wind drifts up to 30-50cm deep. A cold clear night will further improve snow quality and should help break down any rime crust that may have formed in south-east cloud.
Prior to this storm, ridge-lines and slopes previously exposed to south-west winds, were heavily scoured and stripped back to old crusts and scree on upper ridges — these are likely only thinly covered by the new snow. In areas where the new snow was wind affected, it has been scoured down to the old ice crust in places.
Multiple crusts exist in the old snow on all elevations and aspects. Facets (sugary crystals) had 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 50-75cm, 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 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.
Fine with severe morning frosts, then showers spreading north in the afternoon and evening.
WIND AT 1000 METRES
Southerly 30 km/h easing to light in the morning. Southwesterly 30 km/h developing in the evening.
WIND AT 2000 METRES
Southerly 45 km/h but light about the Mackenzie Basin, rising to gale southerly 65 km/h everywhere in the evening.
FREEZING LEVEL
700 metres, lifting to 1200 metres in the morning.
Prior to the new snow on Saturday and Sunday, the old snow was firm and icy in many places. Plenty of runouts had bare rock or scree — these will now only be thinly covered. Slopes exposed to wind, have been stripped back to the crust. 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
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
