Light southerly snow on Saturday night into Sunday may create windslab risk on north-facing slopes.
Beware pockets of stiff new snow on northerly aspects.
As the sun comes out after the storm, loose wet avalanche hazard can rise on sunny slopes holding deposits of new snow.
If overnight snow is blown onto firm north-facing slopes it may develop into pockets of wind slab. Be aware of the indicative signs, including snow blowing off ridge lines and changes in the density of snow on slopes lee to the wind-driven snow.
If precipitation totals rise above the forecast 2-5cm then the hazard may be greater than estimated, so keep checking the snow conditions as you travel through terrain.
Fresh snow deposited on sun-facing slopes will sit over a slick melt-freeze crust sliding surface. Daytime heating may trigger loose-wet releases.
The big question mark is whether things will warm up sufficiently on Sunday, and whether there is much new snow on sunny aspects.
Again, check conditions through the day and as you move through terrain.
A widespread loose wet avalanche cycle was observed prior to the present southerly blast.
Park user observations provide important information.
If you see anything, please report it in the public observations section of the NZAA website.
In most parts of the Park a largely isothermic snowpack is freezing down to a spring structure where concerns exist primarily at surface level. Any new snow on the 15th and 16th will be driven by strong southerly winds and while some may be transported onto northerly half slopes, much will likely sublimate into the atmosphere. Remaining isolated pockets of windslab are likely to exist lee to ridgelines and downslope terrain features and will sit on a very firm MFcr surface. Over the last few weeks winds from all around the compass have stripped higher elevation peaks and ridge lines back to either ice or very firm and now frozen snow. The threshold for avalanches is estimated at around 1500m in the west, tapering east.
Forecast for Sunday 16 August
In the east: Snow showers, affecting Arthur's Pass Road, then turning sleety from midday. In the west: Mainly fine, morning cloud.
Wind at 1000 metres
Southeasterly 60 km/h, easing to 30 km/h in the evening.
Wind at 2000 metres
Southeasterly gale 70 km/h, rising to severe gale 90 km/h in exposed places for a time in the morning and early evening.
Freezing level
700 metres.
Expect areas to be stripped back to hard surfaces from the gale winds at higher elevations. Crampons and an ice axe are a good idea, as many firmer areas now exist.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
