Small to medium sized wind slabs will become more of a threat later in the day as southwest wind increases and loads slopes further. Wind sheltered locations, especially Left and Chute in Tuckerman Ravine, yielded good powder skiing yesterday and also escaped the wrath of the hot April sun. These same aspects may receive more wind loading later today and become increasingly susceptible to triggering. If you are out in the afternoon, be on the lookout for increasing SW wind blowing and cross-loading snow from the alpine into start zones above. Wet loose avalanches may also become a problem, first as sun heats south facing slopes and later as slopes receive some rain or mixed precipitation. These smaller point release type avalanches can have remarkable pushing power as they entrain snow. Monitor your choice of slope for increasingly moist and dense snow and consider the consequences of a slide. Either avalanche type would occur over a bed surface which is icy and hard enough to be a challenge to arrest a fall on.
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Wind slabs will be the primary avalanche concern today, with medium sized avalanches in moderate rated areas causing the most concern. If winds remain as light as forecast, our avalanche problem will be limited to small human-triggered, dry loose avalanches and small to medium sized wind slabs. Avalanche activity early this morning points to the fact that the new snow remains unstable and poorly bonded to older, firm wind slabs and ice crust. While likely to be small, avalanches today may occur on a bed surface which is icy and hard enough to be a challenge to arrest a fall on. Recent avalanche activity and variable spring weather is creating a wide range of snow conditions with older, stubborn wind slabs and a hard, icy crust hiding beneath the low density new snow. Our slopes are not at all the stable corn snow conditions that you might expect for mid-April so continue to reduce your exposure in avalanche paths, carry avalanche rescue gear and manage your risk of long sliding falls carefully.
Wind slab formed since late Sunday is our primary avalanche problem. Generally on the thin side and thus not likely to produce large avalanches, this layer remains possible to human trigger. It will likely vary from stubborn to touchy across the terrain. A secondary avalanche problem is the older and now generally stubborn wind slabs which formed on Friday and Saturday nights, the culprit of our widespread cycle of somewhat small human triggered avalanches over the weekend. This layer is beneath the more recent slabs in some areas and at or near the snow surface in others. Low rated areas have significant old refrozen crust at the surface, presenting a long sliding fall hazard while still holding small pockets of wind slab. It’s certainly a “Low” doesn’t mean “No” avalanche danger kind of day. Moderate rated terrain holds more widespread wind slabs, though it will be difficult for travelers to visually discern thin from thicker slabs as well as the older and more stubborn slabs from the newer and touchier slabs.
Wind slab formed Friday night is our primary avalanche problem, with a secondary problem of smaller wind slab formed from the few inches of new snow that fell on strong W wind last night. The older wind slab has been observed up to 14” thick. It varies in thickness and bonding to the old refrozen crust beneath it, but has gained some strength since Saturday’s widespread human-triggered avalanche cycle. Visibility is limited this morning, but we expect that the new wind slab exists in relatively small pockets throughout the terrain. Today is a “small avalanches in many areas” kind of Moderate rating. We don’t expect any terrain to produce particularly large avalanches, with the old wind slab showing variable stability and the new wind slab suspected to be small. Relatively small avalanches can still bury, injure, or kill a person, especially if they happen in high consequence terrain with rocks, cliffs, vegetation, or other hazards in the runout. If avalanches aren’t enough to make you choose lower consequence terrain, be aware that the refrozen crust which exists at the surface in areas is very hard and could easily allow a long sliding fall.
The 6” of snow that arrived Friday night on increasing west wind formed wind slab in all forecast areas. This wind slab proved touchy to human triggers yesterday with skier-triggered avalanches in Lobster Claw, Chute, Hillman’s Highway and the Little Headwall. Slab depths were up to 14” thick and while nobody was buried, enough snow was entrained to carry at least five people downhill in the Hillman’s avalanche. Size and distribution of this avalanche problem is aspect driven. East facing slopes (Considerable rated areas) contain more widespread wind slab capable of producing large avalanches. North and south-facing slopes (Moderate and Low rated slopes) contain smaller areas of wind slab that could produce a small avalanche.
New snow overnight on increasing W wind makes new wind slab our primary avalanche problem. A lack of visibility into the terrain adds an element of uncertainty to this advisory. We expect the new snow to have trouble sticking to the hard refrozen surface that existed prior to this storm. This indicates two key characteristics of today’s avalanche problem. First, new slabs will likely be touchy to a human trigger. Second, we expect that some areas are scoured by wind to the old refrozen surface. This scouring affect is likely occurring to the greatest degree in our upper start zones. Altogether this means that we have touchy new wind slabs that will vary in size. Largest slabs are expected in middle to lower avalanche start zones of Considerable rated areas, where you are likely to trigger an avalanche. Natural avalanches are possible in these areas, making the floor of Tuckerman Ravine an unwise place to linger. Additionally, be aware that the hard old crust either beneath new snow or at the surface will make it nearly impossible to arrest a long sliding fall.
Until snowfall begins later in the day, the avalanche problem is nonexistent. The greater hazard is long, sliding falls due to the firm nature of the snowpack. Up to 3” of snow may appear by tonight on eventually increasing SW wind. This has the potential to create sensitive wind slab, whose size will largely depend on the amount of snow we receive. If we see the higher end of forecast snow totals (4” by midnight) we potentially could exceed the Low rating in certain forecast areas. Southwest wind will load slopes on the looker’s left side of both Ravines as well as potentially cross-load the Headwall area of Tuckerman and the Central Gully in Huntington. For those recreating later in the day, keeping an eye on how much snow falls and how the wind effects this will be crucial to safe travel.
While isolated pockets of wind slab may be hiding under terrain features in the lee of west wind, these will be small, firm, likely stubborn to trigger, and not the real hazard of the day. The refrozen surface of the snowpack will require filing your crampons and ice axe just to gain purchase. Self-arresting today will be next to impossible, making long, sliding falls one of the two main hazards for the day. The other objective hazard that will have to be dealt with from the moment you open your car door in Pinkham Notch will be the wind. Sustained wind speeds around the century mark will take their toll on anyone long before they reach avalanche terrain.
Huntington Ravine has MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features. Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, and Chute have […]
Isolated, small, and easily avoidable pockets of wind slab exist in the terrain, but long sliding falls will likely be of greater concern for backcountry travelers today. Snowfall and increasing wind late today will add to our wind slab avalanche problem. Avalanche danger will increase slightly after dark today, though any new and unstable slabs that may develop should be small and still best characterized by a Low danger rating. Remember that “Low” does not mean “No” avalanche, and continue to make your own observations for potentially unstable snow on isolated terrain features.
A refrozen snow surface which is hard and icy dominates our terrain, necessitating skilled crampon and ice axe travel on snow slopes. This surface snow will likely not see any softening today. The recent melt/freeze conditions also can result in ice dams, or pressure buildup of flowing water beneath ice, in many of our climbs. A tool, screw, or foot placement can rupture an ice dam. These hazards have been the culprit of serious accidents in past seasons.
Avalanche concerns today are limited to very isolated pockets of wind slab. The half inch of snow that fell yesterday was subjected to strong west winds that likely blew much of this snow down and out of avalanche terrain. Terrain features in the lee of this wind may have collected enough blowing snow to create small pockets of wind slab, but these will be easily identifiable by their white appearance when compared to the gray melt-freeze crust that developed from Friday’s rain. This melt-freeze crust is strong and supportive thanks to cold temperatures over the weekend and presents the greatest threat of the day in the form of long, sliding falls. While two skiers experienced this sort of fall on the Lip yesterday and walked away with no injuries thanks to a clean run-out, the result could have been much different if this had occurred in Left Gully or Huntington, places that have bushes or rocks to contend with.
A significant melt/freeze event on Thursday and Friday generally resulted in refrozen hard snow in the ravines and minimizes concern for avalanche hazard today. If you’re venturing into the terrain today in hopes of spring skiing, you will likely struggle to find soft snow. Conditions will be better for climbers, with crampons, ice axe, and your ability to use them being necessary for travel on snow slopes today. Snow coverage has decreased slightly over the past week, with the Little Headwall transforming to an open stream bed and losing the most snow.
The firm conditions mean that long sliding falls are a key hazard to consider today. The recent warming also means that water is flowing beneath snow and ice. Undermined snow and weak snow bridges over this running water should be respected. Water running under ice can result in the “ice dam” effect, in which pressure builds from water flowing beneath. A tool, screw, or foot placement can rupture an ice dam in a potentially sudden and big way. Ice dams, undermined snow, and long sliding falls have all been the result of serious accidents over the years. Yesterday, a dog had a close call with fast moving water and undermined snow in the Little Headwall but was successfully rescued by people on site.
Huntington and Tuckerman Ravine have LOW avalanche danger today. All forecast areas have Low avalanche danger. Generally safe avalanche conditions exist. AVALANCHE PROBLEM: Due to the melt-freeze cycle the mountain experienced over the past 48 hours, avalanche concerns have subsided for the day. A big drop in temperature following ¾” of rain has locked the […]
Rain on cold, dry layers of snow raises our avalanche danger today. Warm temperatures and rain overnight will continue into the early afternoon hours today, adding strain to the weak layers that exist in the snowpack. There is a good chance that no natural avalanches will occur today, but any avalanche, natural or human-triggered, could be large and destructive. If, for some reason, you venture out into avalanche terrain in the cold rain today, keep this low probability but high consequence avalanche problem in mind. Temperatures will fall to the freezing level this afternoon and continue to drop through the night bringing improved stability to the snowpack. It will also create a hard, icy surface layer that sunshine and cool temperatures tomorrow may have a hard time breaking down.
The warm temperatures that melt bonds between grains in the snowpack and create great skiing and riding conditions also melt bonds deeper in the snowpack. The first strong warming trend tests the strength of the snowpack, and in our case today, creates a low probability, high consequence avalanche problem. Natural and human-triggered avalanches are unlikely in most of our terrain but the threat of a large, hard slab makes it advisable to ski or ride a slope one at a time and to continue to carry your avalanche rescue gear. Large convexities or thin spots would be the most likely locations to trigger this type of avalanche. Wet loose avalanches could also occur in areas with strong solar gain or in the limited areas where soft snow remains. Low avalanche danger does not mean no avalanche danger!
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This website is provided through a partnership between the White Mountain National Forest and the White Mountain Avalanche Education Foundation. The avalanche forecast applies only to backcountry areas, not operating ski areas, and describes general avalanche conditions which vary locally. The avalanche information provided is the sole responsibility of the USDA Forest Service.