March 30th, 2012
Today we headed up into the Byrant Pass area.
We’ve had just under 10 centimeters of new snow in the last
couple of days with moderate winds from the south forming isolated pockets of wind slab up to 20 cm deep in isolated spots. We triggered one size 1 slab avalanche on a steep cross loaded feature just bellow ridge line
The morning was warm and sunny with convective clouds starting to build in the afternoon. The sun was strong when it broke through the clouds and was baking south facing slopes where we found wet snow about 20cm deep. I think the scattered clouds saved us from a widespread wet avalanche cycle today.
Another problem we were wary of with the warm spring temps is cornice
failure, we travelled cautiously whenever we crossed slopes with cornice hazard overhead.
Associated with cornice failure is our old friend, the surface hoar layer
that was buried in mid February. We are
still finding it in isolated areas on North aspects and although we haven’t
seen any recent avalanche activity on this layer lately I suspect that may be due to the
fact that it is hasn’t seen a significant load recently. We've seen cornice failure trigger this layer in the past and it was on my mind again today.
That said Justin and I found some great skiing today especially on east facing slopes that hadn't seen much wind.
April 3, 2012
Another beautiful day in the mountains. We started out by digging our weekly full profile at Fraser Wx plot. Well settled recent storm snow sits on top of a strong and supportive mid and lower snowpack. Compression tests produced no results in the upper snowpack. Compression tests produced no results.
We then headed via snowmobiles to Byrant Lake Pass. Onroute we were observing the North and South facing slopes around Byrant Lake. We were particularly interested in any cornice failures on the North Aspects occurred during the warm temperatures this past weekend. No cornices were observed, however many looked large, drooping with not much support remaining. On the South Aspects, we observed numerous wet loose snow avalanches to size 1.5, predominately originating from cliff bands and rocky outcrops. These all seem to be running within the recent storm snow on an old sun crust.
Convective cells dominated the day and winds were light-moderate from the South, with light snow transport moving around the approx 5-10cms of storm snow that fell overnight.
We skied the NW facing slope that leads down to Crater Lake/Chilkoot pass. The recent storm snow made for good turns. The surface snow became moist around 1200m.
Just wanted to share a picture of the numerous wet loose avalanches we saw today. We also observed a glide crack release on the East aspect of Summit knoll. This is where free water percolates through the snowpack and pools at a basal layer and smooth interface (in this case it is smooth granite rock). This same phenomena can occur with persistent weak layers as well (such as an early season crust that James talks about above). This is usually the culprit for large destructive spring time avalanches.
Of note the Dec 5th crust was down 100cms on a morainal feature at 1500m in the alpine. We observed isothermal temperatures to that layer on a south aspect.
Justin and I are in Fraser this week so we were able to get
an early start in White Pass this morning. Weak recovery overnight with temperatures only going down to
0.3 degrees at both Summit and Fraser wx stations. Skies were broken in the morning with very light winds from
Traveled by snow machine up Waterfall drainage just east and
across the lake from Fraser Highways camp. The slight refreeze overnight made conditions challenging
but doable on the sleds in breakable crust. The weather started to move in once we got in the alpine
with a weak low producing a short storm that killed visibility. The small system was accompanied by
moderate SE winds and graupel in the alpine. Precipitation came in the form of light rain at tree line
elevations during the storm. We
were driven out of the field early by fears that the lake would be uncrossable
with afternoon warming. Our
suspicions were confirmed when we met with moist snow and overflow on the lake
surface on the return crossing.
Through the afternoon the skies again cleared and temperatures stayed
No new avalanches observed today but would suggest paying
attention to normal spring patterns with daytime warming likely to produce
loose wet slides and cornice failures.
Skiing conditions very marginal in the White Pass area with
variable crust in the alpine and isothermic conditions at tree line elevations.
Clear skies and cold temperatures overnight here in White
Pass allowed for a good refreeze in the upper snowpack. Stability was good so we headed up to
north Taiya via Bryant Pass.
Objective for today was to continue to monitor spring conditions at
treeline and in the alpine.
Travel on skis was a little challenging this morning on the
bomber crust that had formed overnight.
Ski crampons are definitely worth carrying this time of year for those
cold, early morning starts. Snow
conditions were relatively good with 5cm of new snow on top of the crust. Despite the intense sunshine,
temperatures in the high alpine stayed relatively cool only reaching about 3C
at midday. Relatively dry snow
conditions on the surface persisted through the afternoon with only a slight
bit of moisture in the surface snow on solar aspects.
On the way up through Bryant Pass on the far side on the
lake we did observe a few slab avalanches to size 2 on sheltered, shaded, north
features. Though these slides are
likely a week old, they are worth mentioning because though we had continued to
suspect further slab activity this spring we had not observed much in recent
weeks. Seeing these few avalanches
confirmed our suspicions and were a good reminder that there are still
persistent weaknesses in the snowpack that we need to be mindful of. This particular avalanche was triggered
on a relatively steep north feature in a shallow area. The slab slid on facets that likely
formed in mid-late February.
So it was a pretty classic spring outing today. We confirmed a good overnight refreeze
and we got an early start. We
planned a descent of a north feature and avoided south aspects during the heat
of the day. We gave cornices a
wide birth and found some decent skiing on a steep north slope and more mellow
Please see photos below in the next post and check the Yukon
Avalanche Youtube Channel for a short video on what we saw today.
It’s been great helping out with the program these last
couple of weeks. Big thanks to
Justin and Eirik for making me feel like part of the team. James.
Natural Slab avalanche failing on a layer of facets. Note the steep rocky terrain, a shallow, weak snow pack area. Think about skiing where the snowpack is deeper, avoiding these type of rocky outcrop slopes. We suspect these avalanches released in the height of the warming trend, approx 1 week ago. The trigger was likely a point release avalanche and/or the warming trend rapidly settling the upper snowpack.
5-10cms of new snow on top of the melt-freeze crust made for good skiing.
Thanks for a great season!
the video referred to in the second last sentence doesn't seem to be up on youtube
Thanks Jim, the video should be up now: Click here to view the video.