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.
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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!
Snow on sun exposed slopes yesterday saw at least some degree of softening, which was followed by a quick refreeze in the afternoon. Areas seeing less direct sun continued to hold dry snow. Avalanche concerns are limited to small loose dry sluffs in this dry snow and loose wet sluffs when the refrozen snow warms again. The snowpack is exhibiting good stability and the current wintry mix of precipitation will not significantly change this. That said, we’re still far from a spring snowpack and it remains wise to travel one at a time in avalanche terrain while carrying a beacon, probe, and shovel.
Spring hazards are becoming prominent and should be considered in your terrain decisions. Long sliding falls on the hard snow, which essentially all steep terrain holds, is a key concern today. If you brave the weather to travel in the alpine, crampons and an ice axe will be crucial equipment. Ice climbers should be aware of potential for ice dams in many climbs which can rupture with the placement of a tool, crampon, or screw. Recent above freezing temperatures has resulted in water flowing beneath ice and can create this hazard.
A significant warm-up today will make loose wet sluffs the primary avalanche problem on sun exposed aspects. Loose dry sluffs are still possible on steep and shady aspects. We expect these small avalanches which could easily knock you off your feet to occur primarily in the few inches of snow which fell late Saturday and into Sunday. The small and isolated pockets of soft and thicker wind slab which formed from that recent snow could begin to act as a wet slab on south facing slopes and should be on your radar in all terrain. The older, widespread, and hard wind slab that is thinly covered in many areas by the newer snow has been unreactive to human and natural triggers and this trend will likely continue. That said, a significant warming like our sun-exposed slopes will experience today can awaken previously unreactive layers at or near the surface. It’s again a reason that “Low” does not mean “No” avalanche danger, and that travelling one at a time, with your beacon, probe, and shovel, is advisable.
Also be aware that while the sun will soften some aspects, others will remain hard, and sun softened snow can quickly refreeze with the return of shade. Crampons, ice axe, your ability to use them, and wise terrain choice are all necessary tools to prevent a high consequence long sliding fall. Sun will also warm ice today, making icefall a key overhead hazard to consider and manage.
Limited wind transport of the several inches of snow which fell in the past 48 hours make loose dry sluffs our primary avalanche problem. Loose snow avalanches won’t bury you today but could knock you off your feet and are possible on most steep slopes. The new snow is distributed fairly evenly across our terrain, though a few areas saw wind scouring and the possibility for small, isolated pockets of wind slab does exist. A firm and generally smooth surface of older snow exists beneath the thin new snow. Conditions are generally edge-able and good for crampon and ice axe travel, but don’t expect to arrest a fall with any ease. A long sliding fall which could be caused by a loose dry sluff or just a stumble is likely your primary hazard to manage today.
Snow that arrived overnight has the potential to form wind slab and loose-dry avalanches. Another shot of snow this morning will exacerbate this problem. While wind speeds should remain mild by our standards, the recorded snow has a very light density, making wind transport possible on low wind speed. Wind speeds should increase slightly this morning to above 40mph. This has the potential to load snow into the northern gullies in both ravines as well as cross-load Moderate rated terrain. With the combination of snow density and wind speeds, expect wind slab to be touchy to a human trigger, particularly with the firm bed surface it will reside on. While northern gullies in Huntington are more in the direct lee of today’s wind, a smaller fetch and confined, steep terrain will make loose dry sluffing more of a an issue. If an avalanche occurs, it is likely to be small, but potentially enough to swipe your feet out from underneath you and lead to a long, sliding fall. As the bed surface in all avalanche terrain is firm, arresting a fall today will be difficult.
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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.