The storm slab remains somewhat unstable on this bed of facets yet with not much precip in the forecast I do not expect any natural avalanches in this layer. Human triggers remain possible as natural avalanches have also been reported in the last 24 hours. Look to see how the snow is bonding at the old snow new snow interface to asses this danger.

The storm slab remains somewhat unstable on this bed of facets yet with not much precip in the forecast I do not expect any natural avalanches in this layer. Human triggers remain possible as natural avalanches have also been reported in the last 24 hours. Look to see how the snow is bonding at the old snow new snow interface to asses this danger.

The National Weather Service Forecasts-

Today- Numerous rain showers and scattered snow showers. Snow accumulation less then 1 inch. Highs around 37. East wind 10 to 15 mph becoming northeast in the afternoon.

Tonight- Mostly cloudy. Chance of rain and snow late. Lows 28 to 34. East wind 10 mph shifting to the south late.

Friday- Snow and rain. Snow accumulation to 3 inches. Highs around 35. South wind 10 to 20 mph shifting to the east in the afternoon.

Temperatures have come up slightly around the region and are hovering close to freezing. Mt Roberts is -1.7c after coming right to 0 yesterday. Eaglecrest is showing -2.7c this morning after a -1c low yesterday. By 2pm today they will again rise right to near the freezing point. Before the weather dries out and cools off a little for tomorrow.

We saw a little more precip than expected yesterday with Eaglecrest picking up about 6cm of new snow from 16.3mm of precipitation. This left a very wet 27% density layer on top of the snows in place. This 6cm is low new snow volumes yet the 16mm of precip is more of a moderate weight load for the new snow to adapt to. The Tram showed even more precip with 9.8cm of snow (nearly 4\") with 21.5mm of precip (a 21.9% layer). This 21.5mm of precip is a considerable weight load for the new snow to adapt to.

Winds have been fairly light over the channel with Mt Roberts showing only 8-10mph winds this am. Eaglecrest is blowing considerably with 19-21mph winds. This has the ability to place considerable windloading on the lee slopes and will create additional danger in windloaded areas.

In general the primary concern today is we have about 25cm (10\") of new snow since the weekend sitting on a layer of facets from the clear cold weather last weak. This 10\" started quite light with 6-8% densities and these layers have continued to get heavier and heavier all week. 10\" isn't much new load but recognize that is sitting on a very weak layer and the snowpack is upside down definitely creating a weak layer.

Yesterday we saw some natural avalanche activity that I was not expecting on Mt Juneau. Chop Gully slid mid day. This was not in my forecast. This shows the weak layers and upside down snowpack may be closer to failure than I have forecasted. Take this into consideration with your decision making process...

Danger today will remain MODERATE> Natural Avalanches may be possible especially in windloaded areas. But for the most part natural avalanches are unlikely and not in the forecast with very little new snow, light winds and steady temps being called for. Recognizing that we had natural avalanches yesterday it is hard to ignore that weakness exists and we are nearing failure in places. This is a foreshadowing that Human triggered avalanches remain possible and may be likely in windloaded areas near summit and ridgeline. Use some caution out there today folks.

Faceted Snow

Angular snow with poor bonding created from large temperature gradients within the snowpack.

Faceted snow:
Faceted snow causes the lion's share of avalanche fatalities in North America with surface hoar as a close second. And no wonder. It seems like made-to-order plot device out of a very scary movie. It grows like a parasite within the snow--often out of sight--until it's too late. It becomes inexorably more and more dangerous during the seemingly most benign conditions--clear skies, cold temperatures--and it lays in waiting, sometimes for weeks, until it's brought suddenly to life by a fresh load of snow or rapid warming. Then, when its victim bumbles into the wrong place, it pulls the rug out from under them, rockets them down the mountain at a terrifying speed, ripping them limb from limb as they bounce off trees and rocks and finally entombs them under tons of icy, hard snow.

How faceted snow is formed:
Faceted snow forms from large temperature gradients within the snowpack. Big word alert!--temperature gradient. A temperature gradient is simply how fast temperature changes over a certain distance within the snowpack. Why? Because it's a fact that warm air holds more water vapor than cold air. This means that temperature gradients also create what we call \"vapor pressure gradients\"--more water vapor in one place than another. And what happens when you concentrate something--especially a gas? It wants to diffuse--move from areas of high concentration to areas of low concentration. When water vapor RAPIDLY diffuses it changes rounded crystals into faceted ones--changes strong snow into weak snow. In other words, temperature gradients create potential weak layers that can kill us. That's why we pay so much attention to them.
Here's another way to explain it. Imagine an old woman with strong perfume walking into a cocktail party. As the perfume diffuses through the room, the people standing nearby would smell the perfume the strongest and the people standing against the opposite wall would be able to smell it the least. Next, pretend that wherever the perfume RAPIDLY diffuses through the room, it changes people to frogs. Soon there would be nothing but frogs around the old woman where the perfume is diffusing rapidly and the rest of the room would stay the same since the perfume around them is diffusing more slowly. Finally, imagine 20 old women with strong perfume spread equally through the crowd. Now, there's no more strong diffusion because the perfume has the same concentration everywhere in the room. Since there's no more diffusion, all the frogs magically turn back into people again.

A stupid example, I admit, but maybe you get the idea. The point is that it's a completely reversible process. Strong gradient turns rounds to facets. Weak gradient turns facets back to rounds. The process in reverse, however, occurs much slowly because it takes so much energy to create a faceted crystal that when we take the energy source away (the strong temperature gradient) it take a lot of time for the crystal to return to its equilibrium state (rounds). In other words, it might take a week or two of a strong temperature gradient to form large faceted crystals but after you take the temperature gradient away, it can take weeks or months for them to stabilize, depending on the ambient temperature of the snow and how much compressive load is on top. In cold climates without much load on top of the faceted snow, it may never gain much strength--even without a temperature gradient. The take-home point here is that: small temperature gradients make the snow stronger; large temperature gradients make the snow weaker. Got that?

So, large temperature gradient?how large is large? For snow of an average snowpack temperature, say around -5 degrees C, the critical temperature gradient is about one degree centigrade per 10 centimeters (1 deg C. / 10 cm.). In cold snow, say colder than -10 deg. C, you need a higher temperature gradient to cause faceting and in warm snow you need slightly less.

For example, let's stick two thermometers into the snowpit wall, one 10 centimeters above the other (about 4 inches). Say we measure a difference of only 1/2 deg. C. in 10 cm., it means that equilibrium snow is growing (snow is getting stronger). If we measure a temperature difference of 2 deg. C. in 10 cm., it means that faceted snow is growing (snow is getting weaker). All you have to do is to find a faceted layer in the snowpack, measure the gradient and you know whether the layer is gaining strength of loosing strength. Cool, huh? This is actually a powerful forecasting tool.