Rising freezing levels and forecast showers on Monday will increase the risk of loose wet avalanches.
Look out also for windslabs lurking around ridge lines and lower down on slopes facing south and south-east.
Trampers beware what is above you when crossing gullies and obvious avalanche paths. Safe travel is one at a time.
If Monday warms up rapidly and rain showers fall on new snow then the risk of loose wet slides will rise.
If the sun comes out, these risks will intensify on slopes facing into the sun (through the northerly half).
Be aware that small slides can quickly gather and entrain snow, building into a more dangerous prospect.
Adjust route plans to suit changing conditions through the day.
Significant snowfalls at higher elevations have increased the windslab hazard on slopes lee to the NW. While these slope are mostly in the south-easterly half, winds can 'wrap around' terrain features creating hazards in unexpected places.
Monday is a day for heightened vigilance and attention to safe route selection.
Beware the telltale signs of windslab including density changes (stiffer snow) and pillows or hard or 'drummy' sounding snow. Avoid convex rollovers and unsupported slopes where windslab is suspected.
A natural avalanche cycle is expected to have occurred during the storm.
Park user observations provide important information. Please help us.
If you see anything, please report it in the public observations section of the NZAA website.
Up to 250mm of precipitation has fallen in western areas of the Park since Friday night accompanied by fluctuating freezing levels. Most areas below ~2100m will have received a snow-rain-snow combination, followed by snow falling to ~1000m on Sunday afternoon. Snow totals remain to be determined once the storm concludes but the threshold for avalanches in western areas of the Park close to the divide is probably around 1500m, tapering to the east. A series of rain on snow events over the past weeks mean rain percolation channels will be well established in the snowpack below ~1800m and new channels will be forming to the highest elevations during this storm's heavy rain precipitation. Strong to gale winds from the northerly half will have formed windslabs on south facing slopes and around terrain features. The underlying snowpack was well consolidated prior to the storm and once drained is unlikely to hold deeper layers of concern for avalanche hazard.
Forecast for Monday 24 August
Showers.
Wind at 1000 metres
Northwesterly 60 km/h.
Wind at 2000 metres
Westerly severe gale 90 km/h.
Freezing level
1200 metres, lifting to 1600 metres in the morning and 1900 metres in the evening.
Wind stripped ridge lines and northerly slopes scoured back to old rain crusts will present a sliding hazard in the coming days. An ice axe and crampons are essential.
Moderate
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
