Observation: Turnagain

Clear and cold weather has maintained much of our great snow conditions for the
the majority of March. The sun has gotten to, and crusted up, many steep southerly
slopes but everywhere else the surface is getting looser by the day and old tracks
and hard wind slabs are being eaten away. We can thank the faceting process for
this.

Many terms are used to describe this kind of loose snow surface. Scientifically
it is know as near surface facets but many folks use terms such as recrystalized
powder, recycled powder, square powder, loud powder, etc. It often has a sparkley
appearance (photo #2) and sometimes, but not always, surface hoar forms on top.

How does this occur?
Basically, clear and cold weather conditions create high temperature gradients
in the top foot or so of the snowpack (see photo). This dramatic difference in
temperature in this top 1-2 feet drives the faceting process. The rule of thumb
says a change in temperatures of 10C per meter (or 1C per 10cm) in a layer of
snow is needed to start faceting. The colder the snow temperatures are however,
the more change you need.

When snow grains become faceted they lose their bonds with their neighbors and
form flat, angular edges (see photo #3). If you grab a handful of snow and it’s so
unconsolidated that there is no way of forming a snowball then you likely have
faceted grains in your hand.

This process can provide us with great riding and skiing conditions during dry
spells but, can also act as a weak layer once it gets buried by the next snowfall.