Monday March 5, 2018
Cornice Fall, Loose Wet, Wind Slab
Travel & Terrain Advice
Things are very stable currently and should remain that way for this entire forecast period. Wind slabs may still linger from mid last weeks extreme wind event so be cautious and observant in the alpine and near ridge top at treeline on N-W aspects. Temperatures will climb into the positive Wednesday and may create loose wet avalanches. While these will be small, loose wet avalanches carry a hefty punch and when combined with terrain traps can be dangerous. Avoid exposure , during this warm period, above cliffs, depressions and tree bands when there are large steep slopes above that are being heated by the sun.
No new avalanches reported over the past forecast period. A few small pinwheels were observed below treeline and treeline on direct solar aspects off trees and rocky outcrops during the clear sunny period mid day Saturday.
After the previous wind events (mid last week) there has been a substantial increased cornice size. Wednesday’s warming may possibly result in cornice failure up to size two. Cornices overhang N-W aspects along alpine and treeline ridges. These failures may happen naturally and with human activity. Stay off cornice edges and don’t expose yourself below cornices as things warm up.
Warm temps Wednesday are likely to cause small size one loose wet avalanches. These will be widespread, will likely trigger naturally and certainly with human activity on all aspects (especially solar) in the treeline and below treeline elevation bands. When associated with exposure to terrain traps below, this avalanche activity may prove more dangerous than one may expect.
Some isolated zones near ridge top on N-W aspects in the alpine and treeline still have wind slabs lurking just below the surface. While the snowpack has gained significant strength, there is a slight, though unlikely, chance that these slabs may still produce avalanches up to size two. Watch for their existence and avoid areas of obvious wind loading, like gullies leading off ridges or large open bowls.
Surface - Very small accumulations of new snow for the entire forecast region Sunday with some of the new precipitation falling as graupel. Widespread Surface hoar from a clear cold Saturday night remains intact and is now buried below the few centimetres of new snow on all aspects at treeline and below treeline.
Upper - These surface layers sit on a second thick and deeper graupel layer, and this covers old snow (from mid last weeks wind/snow event) on non solar locations or over a thin non supportive crust on all direct solar locations (crust due to the clear warm mid day Saturday).
Mid - Well settled and bonded storm snow with multiple thick crusts (including the valentines day crust).
Lower - Well settled .
|Surface||Trace of new snow with graupel and buried surface hoar|
|Upper||Deep graupel layer (1-3 cm) and old snow non solar, thin crust direct solar|
|Mid||Well settled with multiple crusts|
Small accumulations of new snow with convective activity creating some graupel. Solar aspects warmed by a clear warm weather window Saturday afternoon. Clear cold weather Saturday night tightening the snowpack with surface hoar growth. Sunday a trace of new snow and some more graupel during the day. Light winds with little to no snow transport.
Generally benign. Very light snowfall and winds until Wednesday, when things start to warm up ushering the approach of the next big snow/weather event starting Thursday.
Monday - Trace to 2 cm of new snow, light winds from the W, temps around -6 all day, freezing level 0- 900 m.
Tuesday - 1 to 5 cm of new snow, light to moderate SW winds, temps -6 to -4, freezing level 0- 1000 m.
Wednesday - a trace to no new snow, light rising to moderate winds from the SE, temps -4 jumping into the positive near + 1, freezing level 300 up to 1400 m.
Posted on Monday March 5, 2018 by Bill Phipps