Differing weather models make for a tricky avalanche forecast.
Warm temperatures at first and possible rain create a Loose Wet hazard, then hopefully cooling down with heavy snow creating a Storm Slab hazard. Stay tuned for updates through this next storm.
An elevated freezing level and possible rain initially mean Loose Wet avalanches are the one to watch. With an already very moist snowpack, any rain will soften the surface increasing the hazard with extra load and potential lubrication of any crusts within.
If the forecast heavy snow arrives in the afternoon, this will increase the hazard of Storm Slabs. Once we see more than 15cm then Storm Slabs will be possible on all steep terrain above 30 degrees. This is all dependent on the pulse of cold air which is forecast to arrive and produce heavy snowfall. If this cold air does not arrive then this hazard will not be found. Storm Slabs usually occur within the storm snow on weak layers created during the stom when temperature or humidity changes during the storm.
Wind Slabs are more dense and contain smaller snow particles due to being tossed around and beaten up by the wind. These Wind Slabs will be found mostly on Eastern1/2 aspects above 1600m. The stronger the wind, expect to find Wind Slabs lower down the slope from the ridge and in very sheltered zones. Cornices indicate wind direction and could possibly grow quite large with the forecast weather. Watch for denser, hollow sounding pockets of freshly deposited snow on steep slopes above 30 degrees.
Wet Slabs occur when the weight of the snowpack suddenly increases and overloads any weak layers or the ground surface which occurs in very high temperatures or the sudden onset of heavy rain. these Wet Slabs are very hard to predict so avoid any avalanche terrain should heavy rain begin to fall.
2 small (Sz1) Wind Slabs trigged by explosives at Broken River, East asp , around 1700m, 24/08
Snow coverage across the forecast area is super variable. Up to 150cm in some areas down to rime covered rocks. A very 'spring like' snowpack exists at the moment with a few crusts remaining with patches of moist, windblown snow scattered in sheltered zones away from the Westerly 1/2 winds.
Wednesday: Rain with heavy falls about the Divide, spreading elsewhere in the afternoon. Snow lowering to 600m. Gale Northwest winds turning Southeast in the late afternoon. Freezing level 2300m lowering to 1200m in the evening.
Thursday: Rain, heavy at times about the Divide. Snow lowering to 400m about the Mackenzie Basin for a time. Easterly winds turning Northeast and increasing in the afternoon. Freezing level 1200m rising to 2000m in the evening.
Ice axe and crampons are highly recommended as rain will now turn to ice at low to mid elevations. Ski Crampons will be required if adventuring on skis or snowboard.
Low
New Zealand Avalanche Advisory (NZ Mountain Safety Council)
