Avalanche forecast

Ohau

New Zealand Avalanche Advisory
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Avalanche danger

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

A southerly change is forecast for late this afternoon, which will bring snow to lower elevations and expand the wind slab hazard to north facing slopes.

Large avalanches that run below the snowline are possible in the north of the forecast area. Exercise caution travelling through avalanche paths even in the sub alpine (e.g. the Huxley River route, Temple Stream circuit, or northern end of the Ahuriri Valley track).

We are now into day six of this storm with very limited data. It's hard to know exactly what's happening, so maintain a conservative approach.

Avalanche problems

  • Wind Slabs

    • All elevations
    Likelihood
    Likely
    Size
    2

    Another 20-30mm of precipitation is expected today, but across most of the forecast area this will fall as rain before the southerly change arrives late the afternoon.

    Wind slab avalanches up to size 2 remain likely across the forecast area. Size 3 avalanches may be possible in isolated areas on the very highest peaks near the Divide where colder temps mean more snow has fallen. These could run below the snowline, so exercise caution moving under large avalanche paths. Go one at a time, don't stop, and watch out for overhead hazard.

    The southerly change this afternoon will start loading north facing slopes, building fresh windslab on these aspects.

  • Loose Wet

    • All elevations
    Likelihood
    Possible
    Size
    1

    The snowpack below around 2000m has already had plenty of rain in the last 24 hours. Most loose wet avalanches will already have flushed out, but loose wet avalanches remain possible through Thursday.

Recent Avalanche Activity

Observations remain limited by bad weather. Ohau Ski Patrol reported a natural size 1 wind slab on a northeast aspect near ridgeline on the 25th of August, and a natural wind slab avalanche cycle on August 23rd in sheltered terrain near ridgeline, with several size 1 avalanches and one size 2 avalanche on northeast through to south facing slopes.

Current Snowpack Conditions

We still have limited field observations due to the ongoing storm. It looks like roughly 25cm of new snow has fallen in the south of the forecast area since the storm started on Friday, with an estimated 70cm near the Divide above 2000m, with a mix of rain and snow below. Gale and severe gale northwesterly winds have stripped exposed areas back to hard crusts and loaded sheltered terrain.

This sit on a well settled lower snowpack, with slick crusts on solar aspects and shady slopes below 2000m. Faceting has been observed in the lower pack, but after warm temperatures and lots of sun this should be limited to shady slopes above 2000m. We will be monitoring these layers as the storm brings additional load through the start of the week.

Mountain Weather

Rain with heavy falls about the Divide, spreading elsewhere in the afternoon. Snow lowering to 600 metres.

Wind at 1000 metres: Gale northwesterly 65 km/h, changing southeasterly 40 km/h in the afternoon.

Wind at 2000 metres: Gale northwesterly 75 km/h, rising to severe gale 120 km/h in the morning. Changing southerly 40 km/h in the afternoon.

Freezing level: 2300 metres, lowering to 1500 metres in the afternoon, and to 1100 metres in the evening.

Sliding Danger

Gale northwesterly winds have scoured exposed areas back to slick crusts. Take an ice axe and crampons for travel at higher elevations.

Forecast Confidence

Low

  • We are uncertain due to a limited number of field observations.
  • We are uncertain due to the timing of the incoming weather system.

New Zealand Avalanche Advisory (NZ Mountain Safety Council)

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