Vail & Summit County
SnowpackAnonymous · Mar 14, 2013 · Vail & Summit County
Weather
After a cool night, day temps started to warm up fairly rapidly (well above 32F at 11,200); radiation was strong. At higher wind exposed elevations, the wind kept air and snow surface temps cool. Sun exposed slopes showed significant heating, wet surface snow observed even above treeline on S facing slopes.
Snowpack
CURRENT MISPERCEPTIONS 1) Riding slopes that avalanched earlier in the season are safer... Unfortunately, slopes that avalanche reloaded on these same basal facets within a short time, many of them have avalanched several times this seasons! 2) The snowpack's hard mid layers are bridging the weak faceted layers deep down... Let's call it what it is: This "bridge" is a joke! This hard mid layer averages 4-5ft in thickness (hardly enough to provide confidence), varies greatly in thickness and is discontinuous (so much that it would be foolish to bet your life on it), and changes from hard to soft half way down the slope (which is a major trigger point). If you're riding steep and big lines betting this bridging snowpack is going to hold up, just recognize that if you lose, you're losing your life. 3) The lack of instability signs (whumpfing, shooting cracks, collapses) indicates that avalanches are becoming less likely... This assumption may prove a fatal error in judgement as Persistent Slabs tend not to produce a whole lot of instability signs. 4) The warm days are settling the snowpack... This is correct only for the top layer, and predominantly on low and mid elevation sunny slopes. The mid and lower portions of the snowpack remain in full winter conditions, multi layered, highly complex and variable. It will take extensive days of high radiation and warm temperatures to affect the full snowpack. Also keep in mind that such ongoing intense heating of the snowpack will lead to wet slab avalanches. 5) The Avy Bulletin has been posting the same old over and over... Well, conditions are just that. The large faceted snow at the base of the snowpack, 1-4ft thick, has been around since late December and has been creating unstable to very unstable snow conditions ever since. Called Persistent Slab, the persistent nature and the extraordinary extent of these avalanches means that this problem will last well into April. 6) The avalanche danger is only moderate (or perceived as less than considerable)... Avalanche Danger Ratings try to balance "likelihood of triggering" and "consequences (destructive potential)" - this could mean A) low likelihood, high consequences B) high likelihood, low consequences. While early season, scenario B was more commonly the case, things have recently changed to scenario A. While the odds are in the riders' favor, if you trigger an avalanche, it will kill you! Pushing your luck is a bad insurance policy in the mountains. OBSERVATIONS The recent storm snow is starting to bond better with the old snow, especially on sun exposed slopes. Wind Slabs still are found on many leeward slopes and can be triggered by light loads (eg. a skier); these would likely be of smaller size. Such an avalanche in the upper snowpack is likely to step down into deeper layers which will become much larger in size and pack a very hard punch. The main problem still is the Persistent Slab, a weakness deep down, at the base of the snowpack. Snow tests consistently show the huge propagation potential of this kind of avalanche and recent avalanche activity confirms this deep instability with collapses, shooting cracks and avalanches propagating up to several hundred feet. Over the past week, I occasionally observed heinous collapses rumbling into the far distance, shooting cracks propagating several hundred feet, small and large column tests producing results ranging anywhere from very easy to very hard but with very clean failures, small and big avalanches that run surprisingly far and on surprisingly less steep slopes. The snowpack is very complex and highly variable. This season has produced a very weak and avalanche prone snowpack, yet just how bad things are keeps delivering surprises even for professional avalanche workers and guides - trying to pinpoint the snowpack's terrain distribution patterns has become impossible; human triggered avalanches can be expected on slopes 30degrees and steeper around and above treeline on all aspects. Such uncertainty must be managed by cautious terrain selection - backcountry travelers are well advised to keep to slopes less than 30 degrees with no steeper slopes above keeping a respectful distance even in the run out zones.