Friday will bring increasing north-west winds and warm temperatures.
Avalanche danger is likely to increase over the weekend.
Small loose wet avalanches are possible on steep, sunny slopes during the heat of the day.
Watch for roller-balling and signs that the snow is losing cohesion.
Be prepared to change plans and move to cooler aspects.
The wind slab problem will increase as north-west winds strengthen on Friday afternoon.
Watch for wind transport and avoid stiff, wind-pressed snow near ridgelines.
19-20th Aug: Multiple size 1-2 loose snow avalanches ran out of steep terrain on the west side of the Godley River.
18th Aug: Multiple size 1 wind slabs were ski cut at Roundhill. Small loose snow avalanches ran naturally on very steep terrain at Fox Peak. Both were on north-east aspects above 2000m.
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 in the south and east of the range over the weekend. This tapered to 5cm in the west. In places this is capped by a thin rime crust that formed in south-east cloud. The crust is breaking down with cold clear nights.
Tuesday brought strong south to south-west winds, which formed small pockets of reactive wind slab lee to exposed ridges.
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 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.
Mainly fine with morning frost, severe in sheltered places. High cloud passing over from afternoon.
WIND AT 1000 METRES
Westerly 30 km/h, rising to northwesterly 50 km/h in the morning, then to gale 70 km/h in exposed places in the evening.
WIND AT 2000 METRES
Westerly 30 km/h, rising to northwesterly 50 km/h in the morning, then to northwesterly gale 70 km/h but severe gale 90 km/h in exposed places in the evening.
FREEZING LEVEL
2300 metres, but 1600 metres about the divide.
Slopes will be firm and icy until the sun softens the snow. Plenty of runouts have bare rock or scree. 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)
