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Wednesday January 11 2012
Date Issued January 11, 2012 at 08:33PM
Valid Until: Saturday 14th January, 2012. Next update Friday 13 January
| Outlook | Thursday | Friday | Saturday |
|---|---|---|---|
| Alpine |
MODERATE |
MODERATE | CONSIDERABLE |
| Treeline | LOW | LOW | MODERATE |
| Below Treeline | LOW | LOW | LOW |
Confidence: Good.
Main Concerns: (Avalanche problems)
Wind Slab - In the Alpine and exposed Tree Line old wind slabs exist. New redeposited Wind Slab may form with fresh Westerly winds switching to SW South Friday & Saturday, while thin they may be thinner and stiffer they could be sensitive to human triggering.
Persistent Slab - Recent surface hoar on a crust may provide a sliding layer for new snow or wind slab. Additionally instabilities deeper in the snowpack in the alpine only which date from mid November have significant depths of snow on them where they have not failed in recent storms and could produce large avalanches in those areas. While not widespread they could be triggered from thin slab areas, from heavy triggers such as cornice falls, or from wind slab avalanches stepping down to the deeper weaknesses.
Storm Slab - In the alpine only
(above where the rain reached to 1400 m), on all aspects, significant
quantities of storm snow may remain reactive to human triggering in steeper terrain.
Weather:
The Island Alps saw little to no precipitation in the early week. Winds were generally light and East NE. and Temps cooled off. The outlook is for a ridge of high pressure to bring a mix of sun and cloud until Friday when precipitation starts in the PM giving 2cm to 5cm for the East Island and over 10 cm for the West and North Island. The Precipitation continues into Saturday with 5 -10 more again for the West and North and very little to the East side before clearing Saturday. Winds will be generally moderate to light from the West until Friday when SW S winds may pick up to moderate or strong continuing into Saturday. Freezing levels will drop from a high 1700m level Thursday to 1100m and drop again Friday to 600m and continue to cool to near surface Saturday.
Snow Pack:
The island snowpack varies quite a bit from the east coast to the west and north island and is more complex in the alpine than many are accustomed to seeing on the island. Snow pack conditions described below may or may not apply exactly to the area that you are in so local investigation is important.
Up to around tree line the snow pack has been soaked with rain which froze up into a firm crust. Below that are alternating layers of crusts and moist snow. It is a strong snow pack. In the alpine it is a different story. Up to 50cm of storm snow is still settling and has weaknesses within it. Recently formed wind slabs as well as older ones exist on aspects from West through North all the way around to the South East. These will likely be sensitive to human trigger at least for Tuesday if not longer in places. Weak facet/crust layers have been the failure plane for avalanches during previous storms but likely persist in places in the alpine and offer potential for avalanches stepping down to these layers. While these are not widespread and may be difficult to trigger, if triggered they could produce large avalanches. The mid pack in the alpine is strong.
New surface hoar has developed on a crust and may produce weak bonds for future snowfall later in the week.
Avalanche Activity:
Skier triggered avalanche size 1.5 on wind slab in the West Bowl at Mount Cain. See Incident Reports.
Travel Advice:
Thursday and Friday Travel up to the elevation that has been soaked by rain and formed a crust (around tree line) is generally safe. Caution is recommended regarding the possibility of slipping and falling a long way on hard icy slopes.
At higher elevations be aware of old and new wind slabs on most aspects and avoid these specific areas as they will likely be sensitive to human triggering . Be aware that there is the possibility of not only a wind slab avalanches but once started the wind slab may step down to weak layers deeper in the snow pack causing larger avalanches.
Friday PM and Saturday may require Extra Caution in the Alpine with wind redepositing snow and new snow and forming new thin but hard slabs NW N NE E SE Aspects.
Prepared by Niko Weis
Tickets go on sale for the Fourth Annual Party for the Bulletin on Wednesday 11th. Don't miss your chance to attend this now legendary event with live music, silent auction and lots of fun. This is the thing that keeps your source of avalanche info going so come out in support. It all happens at the Riding Fool Hostel in Cumberland on Friday 27 January. More info here.