Potential deep slab avalanche problem.

In the areas with good protection from NE winds, a Deep Slab avalanche problem may develop Thurs-Fri with feet of new snow loading expected. The recent storm snow over old near surface facet snowpack structure has been observed throughout the forecast area on NW-N-NE aspects over the past several days.

Two test pits were dug on Incline Lake Peak today targeting the old near surface facets buried below the recent storm snow. Both sites were N aspect with elevations of 9,240' and 9,250' in near treeline to below treeline terrain. Locations were 39.29846, -119.94299 and 39.29842, -119.94377.

The lower site had good protection from NE winds, the upper site had moderate protection from NE winds with some signs of NE wind scouring. The snowpack structure was similar in both locations with a thicker slab at the lower elevation, more wind protected site. Slab of recent storm snow was layered from surface F hard to mid 4F hard to 1 F hard at base of slab. Facets below the slab were F to F+ hard at dry to moist in both snowpits.

HS and slab thickness at the lower elevation site was  HS 173 cm with 35 cm thick slab and 145 cm HS with 25 cm thick slab at the upper elevation site.

Unstable snowpit test results along the top of the facet layer were observed at the lower elevation site. Lower site tests scored ECTP - 21, ECTP - 24, and PST 25/100 end. Stable snowpit test results along the top of the facet layer were observed at the upper elevation site. Upper site tests scored 2 x ECTN - 16 and PST 37/100 SF and PST 93/100.

SW winds were increasing with only minor amounts of blowing snow prior to 2 pm along the ridgetops. Some surface hoar was present at the snowpit locations but is was already on its side (knocked over) and not likely to present much of a problem.