Bollettino valanghe

Two Thumbs

New Zealand Avalanche Advisory
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Pericolo valanghe

High Alpine · above 1,800 m
2 · Moderato
Alpine · 1,200 m–1,800 m
2 · Moderato
Sub Alpine · below 1,200 m
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In sintesi

A good day with not so much wind to find some softer snow in sheltered areas. Watch any sign of a warming snowpack, like roller-balling and pin-wheels.

Firm snow and exposed rocks still present a significant hazard in many areas.

Problemi valanghivi

  • Loose Wet

    • Tutte le quote
    Probabilità
    Possible
    Dimensione
    2

    The snowpack has warmed up today (10 Aug), but no loose wet avalanches have been reported in the Two Thumbs. Tomorrow (11 Aug) the freezing level might climb to 2000m and warm the snow even more, especially with direct sun or a green-housing effect. This might produce some larger loose wet avalanches North of Stag Saddle.

    However, in the South of the region, we think those will be small as there is little snow available to slide on the wind-stripped northern half. The little new snow has already settle down today. The danger rating in the South will be trending towards "Low".

  • Wind Slabs

    • Tutte le quote
    Probabilità
    Unlikely
    Dimensione
    1

    Winds have eased off and temperatures have gone up. The shallow wind slabs that have developed in sheltered lee terrain (south-west, south and south-east facing slopes) should stabilise with the increasing temperatures. Tomorrow only isolated small slabs at higher elevation may remain. Look out for smooth, rounded pillows of wind-drifted snow, changes in snow texture and hollow-feeling slabs over firm crusts. 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 form the Two Thumbs Range.

In neighboring Cass Valley above Falcon's Nest Hut ,small wets slides were reported from 1700m on W aspect on Sun, 9 Aug. Today (10 Aug) report of small 10cm deep wind slab at top of Scorpion run (S-aspect) - estimated elevation of 2200-2300. .

Similar report form Mt Potts on SUn, 9 August. Very small shallow up to 10cm reactive wind slabs

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

Cloudy with the odd shower, becoming fine in the morning and then cloud returning in the evening.

WIND AT 1000m: Light, northeasterly 30 km/h developing in the afternoon, rising to 50 km/h in the evening.

WIND AT 2000m: Light. Northeasterly 30 km/h developing in the morning, rising to 50 km/h, but gale 70 km/h about Mackenzie Basin, in the afternoon.

FREEZING LEVEL: 1200m, lifting to 2000m north of Canterbury Basin in the morning.

Note: several computer generated forecast models predict the above wind only overnight into Wednesday. We believe during the day tomorrow might be less windy.

Sliding Danger

Firm snow surfaces, exposed ice and rocks are widespread and will present a greater hazard than avalanches in areas previously exposed to the south-west gales. 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

  • The snowpack structure is well understood.
  • We are uncertain about how the timing or intensity of solar radiation will affect the snowpack.

New Zealand Avalanche Advisory (NZ Mountain Safety Council)

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