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
1 · Debole
Sub Alpine · below 1,200 m
Senza grado
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In sintesi

The wind has stripped and moved snow. In the process new windslabs might have developed, but mostly the sliding hazard will have increased.

The best snow is probably stashed at mid elevations in lower angle bowls and gullies

Problemi valanghivi

  • Wind Slabs

    • Tutte le quote
    Probabilità
    Possible
    Dimensione
    1

    Strong winds have continued through the night and until morning on 4 Aug. The strong winds have stripped snow rather than deposited it, but in more sheltered areas and with dropping wind some new windslab might have developed.

    Watch out for cross-loading at mid-slope. The gullies behind those features are the most likely places for wind slabs. However, all our observations tell us that the areas of wind slab are very small and patchy - so be on the lookout for larger pockets. In the mid-elevation band the slabs seem to stick well to the old surface

    It is possible that from the Richmond Range North a new windslab has been layered over already existing pockets of windslab. This might increase the potential slab size.

    Observations around Mt Dobson today, suggest that the Southern tip of the range is very wind-hammered and the danger might be low even around the tops above 1800.

Mountain Weather

Fine with morning frost, possibly severe in sheltered places. Metservice forecasts again Southerlies gale 85 km/h, easing to gale 65 km/h in the afternoon, then 40 km/h in the evening. However, today's (4 Aug) wind forecast was too strong and several computer generated forecast models show only winds around 20-30km/h from the south and Southwest.

It is cold tomorrow with freezing level around 500 metres north of Mt Cook in the morning, then rising during the day and sinking again to even 100m. .

Recent Avalanche Activity

No new avalanche observations over the last 2 days.

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

Current Snowpack Conditions

The snow depth in the range South of Stag Saddle is 40-70cm with some deeper pockets of 100-120cm in sheltered areas. Continuous moderate (1+2/8) than gale (2PM + 3/8) Southerly & Southwesterly have stripped ridges and windward slopes back to strengthening surface crusts or even bare rocks and scree. Up to 20cm of cold wind-drifted, chalky and wind-pressed snow can be found in the sheltered higher bowls - more in the centre of the range and in the North.

Only in the South (around Mt Dobson), we could find sugary weak layers developing around the crusts below the new windslabs. At present, this does not seem a problem. The loading on those weak layers is not enough. Further North the crusts are less severe and the snow above and below seems mostly well bonded with the crusts.

Below the crusts, the snowpack is currently well bonded. Sugary weak snow deposits at the ground are only found around tussocks and bushes.

The snowpack North of Stag Saddle is not well understood, with no direct observations. We know from rain gauges in the valleys that above about 1800m deep snow will now have accumulated in sheltered areas.

Sliding Danger

We have received rain to high elevations, then the temperatures dropped with much wind that refroze and stripped many surfaces. There are many areas with significant sliding danger, in particular in exposed terrain. Also consider that the winds have exposed many areas back to rocks. Check your run-out areas carefully.

Ski crampons will be required! If you like to venture into more exposed terrain tomorrow, then bring an ice axe and boot crampons.

Forecast Confidence

Moderate

  • The snowpack structure is well understood.
  • We are uncertain due to a highly variable snowpack.
  • We are uncertain due to the variability of wind effect on the snowpack.

New Zealand Avalanche Advisory (NZ Mountain Safety Council)

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