Question about facted snow / cold weather / temperature gradient.

[Scottish_Skier]

I was doing some reading and (re)learned the following.

1. Temp gradient > 1 deg C. per 10 cm = snow pack getting weaker (i.e rounds turning into facets).
2. Temp gradient < 1 deg C. per 10 cm = snow pack getting stronger (i.e facets turning into rounds).

http://www.fsavalanche.org/encyclope...ceted_snow.htm

This lead me to think - could a long cold dry period of weather make the snow pack more dangerous on its own?

In typical European conditions the snow pack is usually considered to get stronger and consolidated in the days after a storm. However if the weather remained very cold is it possible for faceted layers buried within the snow pack to become dangerously weak just as a result of just the temperature gradient ? Even though no more new snow has fallen or drifted.... and the snow was previously stable immediately after the last storm ?

Thanks in advance for any reply.

[Sirshredalot]

The sorts of conditions you're describing are much more common in the northern Rockies than in Yurp or the PNW.

In one sense, sure: the snowpack is getting weaker when that happens. You can have increasing weakness brought on by a cold, dry spell, especially early in the season.

In a more practical sense, most of the depth hoar problems that you typically see also include the addition of more snow because you need a slab and a trigger in order to get an avalanche. So the 2 feet that falls around Thanksgiving and turns to rotten sugar over the course of early December becomes a much larger problem two storms later around Christmas.

But let's say you don't get a big avalanche cycle following the storms in the scenario I just outlined. Will the facets underneath the slab formed by the December storms continue to get weaker if you have a cold January dry spell? Yes, they will.

[Scottish_Skier]

Will the facets underneath the slab formed by the December storms continue to get weaker if you have a cold January dry spell? Yes, they will.

^ Thanks for the reply... This answers exactly what I was wondering

[camlax]

not exactly what you're asking but a good way to visualize the concepts.

also, most new research is showing that temperature gradients are such a spatially variable concept and small scale (over less than 10cm) gradients that when extrapolated out end up equaling much larger than 1c per 10cm end up causing just as much damage to the pack.

http://vimeo.com/36026421

rip cora

if i understand your question correctly, you are referring to how in a maritime/ some inter-mountain snowpacks, peak instability occurs during or just after a storm and the trend is downward in the days following. this is the opposite of a continental snowpack where instability will increase due to crystal metamorphism and rapid vapor movement through a shallow snowpack.

in short, yes cold clear weather with rapid vapor movement anywhere in the snowpack can create future issues.

i HIGHLY recommend you read up on dry snow metamorphism.
here is a good intro http://avalancheinfo.net/fixed/weath...amorphism.html

crystal metamorphism is something you can spend the rest of your life trying to understand and read papers or live in a cold lab.
you wont ski much though.

[Scottish_Skier]

if i understand your question correctly, you are referring to how in a maritime/ some inter-mountain snowpacks, peak instability occurs during or just after a storm and the trend is downward in the days following. this is the opposite of a continental snowpack where instability will increase due to crystal metamorphism and rapid vapor movement through a shallow snowpack.

^ well explained.

Wasn't 100% sure if vapor movement through a shallow snowpack during long period of very cold dry weather could result in previously stable and well bonded layers becoming unsafe without any new snow falling.

generally I have assumed that snowpack always becomes more stable in the weeks after a snowfall. though this 'assumption' is based on the places I usually ski and their typical conditions (i.e euro alps & small local hills in scotland)

[ak_powder_monkey]

Your question was about if the snowpack will get weaker on its own. If the temperature gradient at depth is >10°/m then yes, this will lead to depth hoar and thus things will be weaker, however that scenario is just a little bit unlikely. More likely is the surface layer will become faceted (aka recycled powder) then when new snow (either from the sky, or wind) falls on it, it will be especially weak.

[LightRanger]

This happens in CO almost every winter.

I like my maritime snowpack, thank you very much.

[John_B]

I've seen what I believe was small amounts of depth hoar at 2,000 feet in Central Washington after 2 weeks of snow, then a week of clear skis and cold. This was right around Christmas.

[snapt]

This happens in CO almost every winter.

I like my maritime snowpack, thank you very much.

Except the last 2 seasons our (California's) Maritime snow pack had long abnormally cold and dry periods that created some nasty faceting/weak layers that we don't normally see. With climate change and extreme's becoming more normal I don't think the old assumption that Maritime snow packs are deep and stable is as applicable as it used to be. We wen't from uber deep 2010 which had stability issues from the sheer amount of snow, to the last 2 seasons which had much longer persisting week layers due to a lack there of and cold temps.

[icelanticskier]

god i love mid winter rain/freeze events with above hurricane force winds much of the time. pretty much new snow instabilities only.......for a VERY short time.........FTW!!!

rog

[camlax]

Except the last 2 seasons our (California's) Maritime snow pack had long abnormally cold and dry periods that created some nasty faceting/weak layers that we don't normally see. With climate change and extreme's becoming more normal I don't think the old assumption that Maritime snow packs are deep and stable is as applicable as it used to be. We wen't from uber deep 2010 which had stability issues from the sheer amount of snow, to the last 2 seasons which had much longer persisting week layers due to a lack there of and cold temps.

damn this is the million dollar question.
in terms of climate change, (and it is happening, leave the anthropogenic vs natural argument for the political forum) the jet stream shift resulting from decreased polar ice/ a smaller polar high, latitude will be a primary player. this means that the latitude of a the maritime region will have a large role in early season precip/ dry spells. as rossby wave magnitude decreases in the early season, trough size will decrease as well. potential for cold and dry air masses to sit over mid latitude climates will increase.

its still to early to tell. two years of low snow doesn't mean much. it takes 30 years of data to make up a climate period. only time will tell if regions now considered a maritime snowpack will someday have more intermountain properties.

my thought is don't sweat it.

[snapt]

only time will tell if regions now considered a maritime snowpack will someday have more intermountain properties.

My point exactly, it will be interesting to observe if these low tide and more dangerous years become more frequent in traditionally maritime areas. Maybe I should start I thesis.