Faceting?

Given the shallow snowpack and large gradient between the ground and the surface, any idea why we wouldn't be seeing hoar forming? Obviously there's plenty of air space for transport, but is the faceting a slower process when the grains have been saturated into a more consolidated mass, rather than a merely well settled snowpack that hasn't experienced a big rain event?

I need a dumbed down version. I think I heard large temp gradients which I imagined to mean the temp change between the hot and cold temps wasn't quick or dramatic enough to create them? I went to public school.

cookie and marcus, that's my understanding, but it seems like we should be seeing faceting at the ground? That's typically what I saw in CO snowpack during similar temp/weather systems.

Perhaps it is faceting at the ground, but the last 2 weeks haven't been enough time for it to really develop into large crystals...?

I need a dumbed down version. I think I heard large temp gradients which I imagined to mean the temp change between the hot and cold temps wasn't quick or dramatic enough to create them? I went to public school.

The temperature gradients that matter are primarily spatial. Warm dirt and cold sky is the canonical example, but it can happen anywhere that snow is placed between something cold and something warm. The gradients are enhanced right at both surfaces of crust layers, which is why you see faceting both above and below crusts. As Cookie says, it's the water vapor diffusion from warm snow to cold snow that drives faceting/hoar growth.

*******Rank Speculation On My Part*******

I don't know why there haven't been reports of near surface faceting, or maybe I just haven't seen any reports. One possibility is that the facets are very small and appear to be loose snow on top of a supportable crust. Since the rain, there hasn't been much new snow, so a small amount of recycled powder could be less noticeable.

Yes, the faceting process is hampered by very dense snow, the question is - how dense is the snow? Is faceting hampered inside layers of pencil hardness? Knife hardness? I don't have any specific answers. The usual outcome of faceting in very dense snow would be very small facets, or possibly facet formation inside the pore space itself ( which could further increase hardness and number of bonds per unit volume, and therefore, could actually improve stability ). Rare but it happens.

Heat transfer in the seasonal snowpack is very slow, so that is another possible reason why depth hoar has not developed. Heat transfer occurs in the pore space and through the crystals and inter-crystalline bonds themselves. Formation of depth hoar could take more time than has passed up to this point. Usually, depth hoar requires a fairly long growth period.

As others have noted, there aren't very many observations available.

1. Thin snowpack. Does anyone know the average depth?
2. Supportable rain crust above a well-drained snowpack.
3. Some new snow.
4. Very cold temperatures.

Lots of different possibilities here. Maybe the rain crust is protecting the snowpack from harsh environment conditions necessary for moisture transport. In which case, I would expect to see facet development on the underside of the crust. It is also possible ( as noted above and by others ) that the dense layers mean that moisture transport is impeded. But as stated above, you would have to observe the layers to determine the amount of pore space. You would also have to know the layer density and determine if the layer had reached the density of firn, which is ~500 kilogrammes per cubic metre.

"In the one pit I've dug in the last couple of weeks, the snowpack was a frozen brick to the ground -- this was last sunday near Alpental. The snow near the ground was wet, loose rounds -- maybe 4" of 4 finger to fist. We didn't see any faceting, but we didn't break out the lens and really analyze the entire block. No failures on a tap test and shovel shear. "

Just for clarity: How did you determine the crystal forms? Visually? Crystal card? How did you determine that liquid water was present? Did you observe clinging? Just curious, only because I don't have any idea how well you verified your observations and it could be important. ( And this does not in any way constitute any type of criticism of any sort whatsoever. )

Can anyone else describe how their observations were conducted/verified? Sometimes it's important. Again, it's not any type of criticism whatsoever.

Hmm, I am getting a little closer to following along. I guess by dumbed down I was hoping for simple rules of thumb along the lines of "when you have a week of snow in the 30s, a storm ending in rain, and then a high pressure system where it's cold as hell your likely to get them vs. a whatever happened with this last coldspell." Ideally a dirty lymmerick that sums everthing up will be easier for me to remember.