Sunday, March 11, 2018

Spring-like Conditions

Saturday was a spectacular day at Mores Creek Summit, with very few skiers visits and a big snowmobile crowd taking advantage of the good snow conditions and spring-like conditions.

At lower elevations, there was about 5-10 cm of new snow covering a supportable crust. Above 7200, surface snow conditions improved greatly with no perceptible buried crust interface and about 20 cm of new snow that has transformed overnight into diurnal recrystallized "near surface facet (NSF)" snow - what sometimes we accurately refer to "snow that has dried-out". This is accurate due to the fact that during the faceting process a volume of snow mass is lost to sublimation, as the precipitation snow is sublimated and deposited within the snowpack as facet crystals.

Above the new NSF we observed a widespread layer of surface hoar formed overnite.

Surface hoar across my ski tips 
By the end of the day, the warm temps and strong solar radiation had destroyed the surface hoar at all aspects with the exception of deep north slopes.

The first run of the morning was a surprise. Surface snow conditions were better than expected.
Almost Top of The World - 1st run of the day
We recognized that today's warm temps and intense solar radiation were going to impact the snow rather soon, thus we set our bearings into Whoop-Em-Up headwaters.
Whoop-Em-Up Headwaters Avalanche Path
We were fortunate that a party skiing at Whoop-Em-Up on Friday did not ski the avalanche path below the cornice. 😄Thanks! Turns were sweet, but it had enough "east" and we knew it would not stay powdery for too long. We spent the rest of the day at the more northerly slopes of Whoop-Em-Up headwaters.
Whoop-Em-Up Headwaters North aspect slope
Eric contemplating where to lay tracks next
A week ago there where three reactive layers at MCS; two storm slabs at 35 and 60 cm, and a persistent slab at 95 cm. Predictably, the storm slab problem reactivity was already decreasing by last Sunday. We did not find any evidence of instabilities associated with the precipitation event a week ago.

The persistent slab problem at MCS is found in specific areas such as shallow low elevation aspects (fortunately where we do not like to ski!) and at rocky and shallow northerly aspects above 7600. Those familiar with MCS recognize that these specific features are rare and easily recognizable. Besides, MCS skiers and sleds go for the readily available deep snowpack and rock-free areas to play in the snow.

As we skied down Lamar ridge the impact of solar radiation and warm temps became unmistakable - snow surfaces at east aspect slopes were saturated with liquid water. And it did not matter how good was the wax job in your ski, the ski difficulty level went rapidly up! 😰

It should be noted that we carefully selected a safe route down a south aspect slope with a shallower snowpack. At one point the "full" slope (under 30 degrees) fractured as I skied across it and energetically and unapologetically whumped as it collapsed few cms down in unison. A steeper slope would have avalanched. This instability is well known - a persistent slab at lower elevations. This instability was not related to either a wet loose or wet slab problem. It was simply the reactivation of an old persistent problem due to "snow creep" caused by warm temperatures creating traction at the slab and polycrystal/facet layer interface. This is the interface that Payette Avalanche Center continues to warn us about it, and that can be found at MCS.

Last Wednesday I went early in the morning with the intention of skiing the northwesterly aspect slopes of Mack's Creek, below Bogus Basin "Triangle" ski area and to do snow research work for the Avalanche and Snow Physics class I am supporting Hans Peter Marshall teach at Boise State Unversity.
North-westerly slopes above Mack's Creek near Bogus Basin
I desisted in doing some side-country skiing after realizing that the snowpack at Bogus Basin backcountry remains shallow, and I did not feel like dealing with brush-covered slopes. The skiing at Mack's creek can be quite good since the snow is protected from winds and solar radiation. Below a sample of pictures from last March 2017.
Top of Bogus Basin from Mack's Creek NW aspect slopes.
Cold snow at Mack's Creek
Mack's Creek slopes from Bogus Basin
Instead of skiing, I identified a side-country slope near the Bogus Basin access gate for Mores Mountain, where I spent part of the morning doing snow research.
During snow, research scientists record snow layer depths normal to the snow surface, not "plumb"!
Very rare event - Two Denoth instruments in the same pit! Thre are very few snow capacitance instruments in the world (Expensive).
Using capacitance plates to measure the snow resistance to an electromagnetic field (a physical property called permittivity).
The experiment required to have a dry snowpack. I was generating data for a BSU GEOS 466-566 class homework where students evaluate the use of a capacitance-based sensor to estimate snow density.
Capacitance measurements versus snow density (gm/cc)
Capacitance sensors are almost always used to estimate the amount of liquid water in the snowpack. But when the snowpack is dry, the capacitance sensor estimates the resistance of snow to an electromagnetic field. This property is referred as permittivity, and in a snowpack free of liquid water permittivity is a function of density. Snow science is soooo COOL! 🤓

A final topic to write about, and I must declare that I am uncertain how to communicate to the timber sled users. Mores Creek summit coexistence between snowmobilers and backcountry riders is something I feel proud about it. We depend on each other. I feel safer with the presence of snowmobilers. I KNOW they are my HELPLINE if an emergency arises! Also, the snowmobile community has gone out of the way NOT to impact the area accessed by backcountry riders. I respect them greatly for that.

Last year I started to observe timber-sleds accessing terrain used by skiers. I considered these occasional incidents as part of the learning process for these new "timber-sled" users. Besides, I always espoused the belief that MCS is a large area, and the perception of crowding is the result of lack of imagination of where to go skiing. However, I was deeply concerned about the unsafe manner timber sleds traveled through steep terrain - cutting sideways through significant distances. This is annoying to some of us that care about the aesthetics of ski lines since large tracks of ski terrain get unnecessarily impacted. The truth is that this season I had seen many skiers doing the same with their uphill tracks!

This past Saturday as I skied down to the I-21, it was hard not to notice the significant timber-sled side-hilling across the terrain used by skiers next to Almost-Top-of-the-World (see pictures below).
Timber-sleds tracks across slopes next to "Almost-top-of-the-World.
Timber-sleds tracks across slopes
In the meantime, timber sleds need to be made aware (and some backcountry riders too!) that it is NOT SAFE to sidehill steep slopes. There is a BIG-BIG-BIG difference when sleds go uphill/downhill on a slope in contrast to going across the full slope width in what appears to be an attempt at finding the weak spot in the slope. And the awareness needs to also include the fact that timber sleds are required "snowmobile" registrations. And that state of Idaho requirement is being short-circuited by some timber sled users. I close this topic asking the snowmobile community to try to mentor the timber sled users. I realize it is unfair to ask you to carry this burden, but the truth is that you are in a better position than the backcountry skiing community, since motorized users share the same passion for winter recreation with power machines.