Signs of potentially problematic buried surface hoar on Silver Peak.

Location Name: 
Silver Peak
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of observation: 
Tue, 01/23/2018 - 12:00
Location Map: 
United States
39° 13' 35.292" N, 120° 14' 22.488" W

Red Flags: 
Obvious avalanche path

Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

Buried 1 to 3 mm surface hoar was found on open N-NE aspects below treeline on Silver Peak. This layer was buried just 4 cm (2 in) below the snow surface, so not a problem until buried deeper by new snow loading. With high confidence for 7 to 14 inches of new snowfall forecast above 7,000' for Jan 24/25, the potential exists for this buried surface hoar layer to become problematic.

This weak layer was tested today at the snowpit location using techniques similar to the 2016 Birkeland and van Herwijnen method to examine how the weak layer may respond to future snow loading. A 20 cm (8 in) thick slab was built on top of the snow surface using disaggregated snow. The slab was allowed to sit and sinter for 50 min prior to performing a PST. Results from the PST on the buried surface hoar layer with 20 cm artificial overlying slab scored PST 3/100 end. This is a strong indication that this layer will respond poorly to new snow loading.

Of interest, today's snowpit at the noted lat/long was at the site of a natural avalanche failing on buried surface hoar sometime on January 16 or 17, 2016.

Near treeline, up to 15 cm (6 in) of recent storm snow existed along tops and windward sides of the E ridge of Silver Peak. With strong to gale force SW winds forecast pre-storm on Jan 24, there is significant snow available for wind loading and wind slab formation onto the N aspect avalanche paths along the E Ridge prior to the onset of new snowfall.

Some areas of surface hoar up to 5 mm in size were noted on the snow surface in isolated areas on N-NE aspects in open areas below treeline.

Snowpit or crown profile photo or graph: 
Snowpack photos: