Avalanche Forecast for Friday, February 1, 2019
This information was published 02/01/2019 at 7:06 AM.
The Bottom Line
Wind transported snow has created our avalanche problem today. You’ll find these wind slabs in terrain that faces mostly east, beneath steep terrain features, and cross loaded into gullies and features in a wider portion of the compass rose. The slabs will appear smooth and chalky and will be firm but edgeable with boots or boards. They’ll also be hollow sounding and could crack and avalanche, especially at thin spots near the edges of thick slabs. The January 24th rain event that smoothed out all the earlier snow is now an exposed ice crust in many areas and makes a slick and planar sliding surface beneath these wind slabs. Crampons and an ice axe will be extremely useful in areas where wind scouring has exposed the crust but will give you options for avoiding wind slabs on the way up. Avalanche danger varies widely by aspect and elevation, but the possibility of human triggered avalanches tips the danger rating into the MODERATE range where medium to large size avalanches capable of burying a person exist.
Temperatures have remained cold in the past 24 hours with a high of -18 F and a low of -27. No new snow has fallen, though wind from the west, averaging 70 mph and gusting to 100, has resulted in blowing snow observations at every hour of the past 24. It is currently -22 F with wind from the west at 80 mph. Summit fog will begin to clear this morning with wind diminishing through the day, reaching a more tolerable 50 mph by dark. High temperature today will rise to around -10 F on the summit, 10F in the notches. Temperature will moderate some tonight and tomorrow though remain burly with new snow potentially challenging visibility and increasing avalanche danger tomorrow. At this time, Sunday looks like a warmer and less windy day for playing in the Ravines.
Primary Avalanche Problem – Wind Slab
Wind slabs, some of which will be large, are the main avalanche concern today. Strong winds have blown snow on the ground from the west to east facing terrain. These wind slabs are likely to be stubborn but should be approached with the kind of caution that this high consequence, low probability problem deserves. Smaller but potentially more reactive wind slabs may exist in sheltered areas.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Fourteen inches of snow fell in the middle of the week. Cold temperature kept this snow dry and easy to transport into our easterly terrain and created touchy and reactive slabs that required staying on low angle slopes on Wednesday. The cold weather likely slowed the sintering and bonding process between layers formed this week. While natural avalanche potential is unlikely today, the recency of the new wind slabs, a steep, icy planar bed surface with few anchors remaining, and continued though minor loading could still tip the scales somewhere. Without field observations and assessment, it would be unwise to assume that avalanche danger is low in wind loaded terrain but it is almost certain that the specific areas mentioned in the bottom line create a high consequence, low probability avalanche problem. Easing into the terrain and careful travel techniques could yield some smooth turns and good booting and cramponing if you can withstand the cold and wind.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. The annual MWV IceFest this weekend draws climbers from all over New England to the mountains this weekend. The White Mountain Avalanche Education Foundation will be at the event on Saturday night and Frank will give a brief presentation about terrain management and avalanches in Huntington Ravine.
Safe travel in avalanche terrain requires training and experience. This forecast is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 02/01/2019 at 7:06 AM.
USDA Forest Service
White Mountain National Forest