Avalanche forecast

Two Thumbs

New Zealand Avalanche Advisory
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Avalanche danger

High Alpine · above 1,800 m
2 · Moderate
Alpine · 1,200 m–1,800 m
2 · Moderate
Sub Alpine · below 1,200 m
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Highlights

The storm is here! Northerly strong wind, rain and snow above 1700-2000m until Thursday (13 Aug) afternoon.

Wait until the precipitation subsides and travel away from steep and lee terrain.

Consider loose wet avalanches on South-east aspects!

Avalanche problems

  • Loose Wet

    • All elevations
    Likelihood
    Likely
    Size
    1.5

    Despite the warm air temperatures, few to no loose wet avalanches have been reported in the Two Thumbs until the evening of 12 Aug. However, the rain has started to fall and will soften the hard crusts and hard snow that did not warm up with solar radiation. This might produce some loose wet avalanche activity across the range.

    South of Round Hill, we expect only small avalanches with the small forecasted precipitation amounts, but it will mainly be rain to 1700m or higher.

    Further North with accumulation of wet snow and more rain on a thicker snowpack, the loose wet avalanches might get bigger.

    Watch the East to South East aspects in particular. Here the softer snow was preserved and may now release with the rain.

  • Wind Slabs

    • All elevations
    Likelihood
    Possible
    Size
    1.5

    Strong Northerly winds and some new snow above 1800m are likely. The combination could build reactive new wind slab lee to the winds near the tops or high ridge lines.

    The slabs will remain small in the South and get bigger further North in the range. Consider that a cornice fall or natural slab from above 2000m, might trigger a loose wet avalanche lower down and further increase the size.

    Look out for smooth, rounded pillows of wind-drifted snow, changes in snow texture and hollow-feeling slabs over firmer old snow. Think about terrain selection in steep alpine terrain, particularly where even a small avalanche could carry you into rocks, gullies or over cliffs.

Recent Avalanche Activity

No avalanche observations from the Two Thumbs Range.

In Aoraki / Mt Cook National Park closer to the Main Divide loose wet activity was observed on Monday 10 Aug

If you see any activity on the Two Thumb Range, please make a public observation. It helps us to produce accurate forecasts.

Current Snowpack Conditions

Southern end of range — south of Stag Saddle

Ridge-lines and slopes exposed to the south-west, have been heavily scoured, and mostly stripped back to old crusts, or even bare rocks and scree on upper ridges. Firm crusts and areas of wind-affected snow are widespread, with the most scoured and variable conditions found in the high alpine, and at the southern end of the range.

Sheltered terrain above 1600m continues to hold soft snow.

Sunny slopes have been softening from late morning.

Snow depth varies from 40-70cm, with deeper accumulations of 100-120cm in sheltered areas.

Small facets (weak sugary crystals) have begun developing around crusts in the upper snowpack and between layers of old wind slab, particularly on shallow shaded slopes. At present, these are not posing a significant problem. Below the crusts, the lower snowpack is well settled.

Northern end of range — north of Stag Saddle

The snowpack north of Stag Saddle is not well understood, with no direct observations. We expect that deep snow will have accumulated in sheltered areas above 1800m.

Mountain Weather

Rain about the Divide, easing in the morning. Isolated showers elsewhere, clearing in the afternoon as fine spells increase.

WIND AT 1000m: Northerly 60 km/h, easing to northwesterly 30 km/h before dawn.

WIND AT 2000m: Northwesterly gale 75 km/h, easing to westerly 30 km/h in the afternoon.

FREEZING LEVEL: 2400m, lowering to 1900m about the Mackenzie Basin in the afternoon.

The meteoblue AI supported forecast model has produced some of the better forecast for our region recently. We may get an ok day in the Southern Two Thumbs, with the North to Northwest winds easing back in the late morning and about 5-10cm of wet new snow above approximately 1700m.

The further North, the longer the weather will stick around and the more snow will fall above the 1700m elevation. Maybe 10-15cm at Stag Saddle and potentially over 30cm from Captains Peak North.

Sliding Danger

The warm weather and the rain that appears to have started from evening of 12 Aug have softened all surfaces. In the South in particular, slick snow and icy patches exposed by the south-west gales are still about. A slip or fall on steep terrain could have serious consequences, particularly above bluffs, in gullies or where runouts are confined.

Take extra care when travelling on hard snow, 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.

Forecast Confidence

Moderate

  • We are confident the likelihood of avalanches will increase with the forecast weather.
  • We are uncertain about forecast snowfall amounts.
  • We are uncertain if precipitation will fall as rain or snow.

New Zealand Avalanche Advisory (NZ Mountain Safety Council)

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