South Columbia

Variable reactivity of the mid-December crust/surface hoar interface is challenging to deal with. Stay disciplined and continue to seek out conservative terrain options.

Fair

An upper ridge continues to shift the storm track into the Alaskan Panhandle.  No new snow is expected for the three day forecast period.  Winds are expected to remain very light out of the W/NW at treeline and moderate NW at ridgetop.  The freezing level looks to remain at Valley Bottom until Wednesday afternoon when it is expected to rise as warm SW air begins to invade the province.

A skier intentionally triggered a size 2 avalanche at 1700m on an east facing moraine in the neighboring Glacier National Park region on Saturday.  This avalanche failed on the mid-December crust/surface hoar.  In the south of the region a skier triggered a small but slow moving hard slab avalanche that also failed on the mid-December crust/surface hoar.  Interestingly, this feature had previously slid and was thus reloaded.

While there are exceptions, for the most part a breakable surface melt-freeze crust can be expected on all aspects below approximately 1800 m and on sun-exposed slopes above. Recent warm temperatures have aided in the settlement of the nearly week old storm snow. This snow adds to the depth of the persistent slab which is now 80 - 140cm thick.This thick slab rests on the mid-December surface hoar/crust persistent weak layer (PWL) which remains sensitive to human triggering. This PWL continues to produce widely variable results from very easy shears to no shear at all which isn't very confidence inspiring. The trend shows that easy to moderate sudden planar shears and the resulting human triggered avalanches are most likely at and below treeline. The absence of crust at upper elevations is thought to make the slab less reactive in the alpine, but we're not receiving much in the way of observations from that vegetative/elevation band.