Todd Ridge - hunting for buried surface hoar

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Updated:
Monday, Dec 10, 2018 7:11 PM
Observer(s):
Aaron Hartz
Position:
Pro Ob
Location:
Three Sisters Area (44.033813, -121.704140)
Ob Date/Time:
Mon, Dec 10, 2018 - 5:13 PM
Report Type:
Snow Conditions
Mode of Travel:
Ski or Snowboard

Written Report:
Last week, many people were finding surface hoar around the central Oregon mountains. These feathery crystals do not pose a threat when they are on the surface but when they are preserved and buried they can create a weak layer in the snowpack. Today, I toured around the Todd Lake/Ridge area to check for buried surface hoar. Since the region received 8cm (3") of new snow last night, I wanted to see if the surface hoar was present under the new snow.

Buried surface hoar was present 8 to10 cm below the surface, and in various states of decay. It was found directly below a melt freeze crust; the melt freeze crust was below the new snow from last night. In the flat meadows near the lake, along the east facing slopes, and atop Todd Ridge, the surface hoar was broken and mostly laying down, presumably less likely to be a point of failure in the snowpack.

On a northerly aspect below Soda Peak (elev. 6950ft) the buried surface hoar was more intact and standing more upright. In this area the hoar layer was about 2-3cm thick (see pictures). It failed during compression tests, but there was no propagation during an extended column test (see details below).

This buried surface hoar layer is something to examine in a variety of areas in the days to come. It could be more preserved and reactive in some areas that remained shady and colder in previous days. This will be especially important since the weather forecast is calling for significant snowfall in the next few days. With additional loading of snow on a sensitive weak layer, a slab avalanche problem may arise.
Anybody touring on northerly/shaded terrain should watch for signs of unstable snow such as a collapsing snowpack and whumphing sounds that are oftern associated with buried surface hoar. If you experience these signs retreat to lower angle terrain (less than 30 degrees steep).

I observed no red flag signs of unstable snow (i.e.no cracking, whumphing, or collapsing in the snowpack).

Ski quality was pretty good with the 8-10cm of new snow on top of the melt freeze crust. Snow coverage is still thin. and many small trees and logs are poking through the snow.

Additional snow and weather details:
Location: Soda Peak Elevation: 6950
Aspect: North Air temp: -3C (27F)
Height of snow: 80cm New storm snow: 8cm
Wind: Calm Sky: Overcast
Precip: Snow (less than 1cm/hr)
CTM RP down 10cm - in the buried surface hoar
CTM PC down 10cm - in the buried surface hoar
ECTN 13 down 10cm - in the buried surface hoar (no propagation)




Weather & Snowpack
Temperature: -3°C Precip: S-1 Very light snow
New Snow: 8 cm Snow Depth: 80 cm Elevation: 6950 ft


Multimedia

Caption: Upper pack snow structure near Soda Peak

Caption: Close up of buried surface hoar near Soda Peak