The avalanche hazard will rise to considerable on Thursday afternoon as gale northwesterly winds and rapid snowfall create new wind slab. Conservative route planning is essential.
Increasing wind and precipitation will build wind slab on sheltered northeast, east and south facing slopes near ridgeline on Thursday. These slabs will become larger and more destructive with rapid snowfall forecast in the afternoon.
Watch for signs of wind slab such as blowing snow; stiff, hard, or textured snow; or deeper wind drifts.
Precip should push past the divide and into the east of the forecast area on Thursday afternoon. Rain on snow could trigger small loose wet avalanches, especially on steep, shady slopes that are still holding unconsolidated snow.
No new avalanches have been observed in the last 48 hours, but observations from Wednesday were limited by bad weather.
A few centimetres of new snow has fallen about the divide since the storm arrived on Wednesday. This snow, and the loose snow from the previous storm on the 24th and 25th, is being redistributed by strong to gale west and northwesterly winds. The upper pack will be a mix of crusts from sun and wind scouring on north and west facing slopes, with windslab in deposition zones near ridgeline on east and south facing slopes, and faceted powder in sheltered areas. This sits on a stout rain crust from the 24th of July below 1800m. The lower pack is generally well settled.
Showers, some heavy with snow to 1400 metres.
Wind at 1000 metres: Northwesterly 45 km/h, rising to gale 65 km/h at night.
Wind at 2000 metres: Gale northwesterly 65 km/h.
Wind at 3000 metres: Northwesterly gale 70 km/h.
Freezing level: 1700 metres.
Strong to gale northwesterlies will start to form slick crusts on exposed slopes by Thursday morning. If you must go out in the storm, then an ice axe and crampons are recommended for ridge travel or travel in the high alpine.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
