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RegisterJan 31st, 2015–Feb 1st, 2015
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Shallow storm slabs are possible Sunday afternoon. Watch for new snow that bonds poorly to existing surface crusts or in areas of preserved surface hoar. There is still some uncertainty regarding persistent slabs east of the crest, however recent reports indicate overlying strong snow layers are limiting the potential for human triggering.
Generally very light precipitation is expected Sunday morning, with light rain and snow in the afternoon along the Cascade crest. A frontal passage is expected later Sunday afternoon and should lead to a slight warming trend late in the day along the east slopes.
New snow may bond poorly to surface crusts, allowing shallow storm slabs to develop Sunday afternoon especially on lee aspects near and above treeline. New storm slabs may also fail on surface hoar that survives on shaded aspects generally below treeline closer to the Cascade crest.
Warmer weather is allowing persistent weak layers from January 15th to become less or non-reactive. This problem will be listed as unlikely for the northeast and central east zones.A fair amount of uncertainty surrounds a potentially stronger frontal system Monday but generally expect increasing avalanche danger Monday.
Last weekend (Jan 24-25th) a warm weather system caused high snow levels and light rain east of the crest. NWAC sites east of the crest had up to an 1 inch of rain. This caused loose wet avalanches, some possible wet slab avalanches and consolidation.
Mainly mild or sunny weather has been seen so far this week at upper elevations with low clouds or fog mainly below about 3000 feet.
Recent Observations: Extensive surface hoar growth was seen between about 3000-4500 feet where recent low clouds or fog have persisted east of the crest this week.
On Jan 25th, the Mission Ridge ski patrol reported that depth hoar at 45 cm below the surface was becoming rounded but still failed on isolation. NWAC pro-obs or North Cascade Guides reports this week in the northeast and central east zones have found the January 15th facet/crust layers at 40 cm-1 m below the surface with the facets starting to turn to rounded grains and not reactive or not releasing in pit tests. So the January 15th facet/crust layers expected in the northeast and central east zones should be strengthening and stabilizing.
NWAC pro-observer Tom Curtis was at 7500 feet on Mt Cashmere in the Wenatchee Mountains on Wednesday and found a local facet/crust combo buried on a lee slope next to a ridge crest under 35 cm of thick, surface crust and 1F-P snow. This sort of slab could be very hard for a skier to trigger, but could be possible, perhaps with a large sudden load, such as snowmobiles.