This information was published 12/10/2018 at 7:04 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Smaller areas of softer wind slab that exist on many aspects and are reactive and keeping our rating at MODERATE today. These have been found primarily in sheltered areas of the strong W and NW wind, though do exist on most aspects. While these formed at the end of last week, cold temperatures have prevented much settlement or bonding, keeping these small areas on the forefront of our mind. Larger areas of firm wind slab exist as well and while these are stubborn, their potential size could be large if the trigger point is found. Today, heightened avalanche conditions exist on specific terrain features that will need to be identified and evaluated.
After a cold and windy weekend with a less than one inch of new snow falling on the Presidential Range, another cold front will move into the region today. Temperatures on the high summits will stay in the single digits F with NW wind between 40 and 50 mph. No new snow is expected today with clouds and fog looking to clear out by afternoon.
Primary Avalanche Problem – Wind Slab
Wind slab of varying hardness and thickness exists in much of avalanche terrain, but the area of biggest concern will present as softer surface snow. These softer areas have proven reactive to human triggers in steep terrain, however, overall size seems to be small. The second wind slab problem is firmer and much bigger in area and thickness, but stubborn to triggers. This firmer slab potentially could be propagated into from an area of softer slab or even from a thin spot in the snowpack, but we see this as unlikely.
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.
Field observations are reporting a mix of scoured areas, areas of firm but edgeable wind slab, as well as smaller areas of softer snow. The snow of concern exists above the melt-freeze crust that developed one week ago. These areas of softer snow are the big concern and are being found in sheltered areas of terrain features. The surface of problematic areas is four-finger (4F) hard with a layer of fist hard (F) underneath. We have one report of this producing a skier-triggered avalanche in South Gully of Huntington while stability test observations on south, east, and north facing aspects are reporting this failing with very easy to moderate fractures.
Thank you for submitting your observations! We love feedback from the field and it’s greatly helping our program. Keep them coming and be sure to check them out yourself here.
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 12/10/2018 at 7:04 AM.
USDA Forest Service
White Mountain National Forest
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