Monday December 17, 2018
Storm Slab, Persistent Slab, Loose Wet
Travel & Terrain Advice
Take note of changing conditions as you move through elevation bands. Avoid overhead hazards and be aware of paths that may originate from higher terrain. Pay close attention to the presence of shooting cracks and/or whumpfing as you travel. Below treeline, creeks and early season conditions prevail.
Very little alpine observations during our recent storm cycle. No natural activity seen or reported with the exception of several size 1 loose wet avalanches on all aspects below treeline during recent spikes in freezing levels. Shooting cracks and whumpfing have been reported on all aspects at treeline.
The recent onslaught of Pacific frontal systems will very likely produce large to very large (size 2 to 3) storm slabs on all aspects and wind slabs in lee terrain especially at treeline and in the alpine. These slabs may be easily triggered by light loads in many areas.
Recent large storm snow loads sit on top of a weak crust/facet combo that has the possibility to produce very large (size 3+) avalanches on all aspects mainly at the alpine elevation with the application of a large load. I.e. cornice failure.
Lower elevations will very likely produce small (size 1) loose wet avalanches on all aspects with increased freezing levels and rain load.
Recent moderate to heavy precipitation and strong to extreme southerly winds have deposited up to 2 m of storm snow with variable distribution above 1400 m on top of a melt freeze crust with weak facets below. Lower elevations have seen much of this precipitation as rain. Above 1400 m a poorly bonding density change buried 60-90 cm deep has produced moderate results with a propensity for propagation. Testing on the weak facet/crust layer has also shown sudden planar results which suggest a large load like a cornice failure could have potential to trigger this deep instability. Below 1400 m, surfaces are moist to wet.
|Surface||Above 1400 m, 20-30 cm of dry loose storm snow. Below 1400 m moist to wet.|
|Upper||Above 1400 m, 50-60 cm of unconsolidated dry storm snow.|
|Mid||Rounding storm snow with varying densities.|
|Lower||Lower 20-30 cm melt freeze crust/facet combo.|
Last week we experienced moderate to heavy precipitation and strong to extreme southerly winds across the forecast region. Freezing levels have been hovering around the 1100-1600 m mark with the snow level between about 900-1400 m.
MONDAY - 50 to 80 mm of precipitation with freezing levels around 1200 m and strong SE winds. Freezing levels will spike to 1600-1700 m Monday evening. Expect lower precipitation amounts and freezing levels in the northern regions.
TUESDAY - 30 to 50 mm of precipitation with freezing levels around 1100 m and strong to extreme SW winds.
WEDNESDAY - 10 to 20 mm of precipitation with freezing levels dropping to 900 m and winds easing to moderate from the south.
Posted on Monday December 17, 2018 by Dan Goodwin