Avalanche Forecast for Tuesday, December 11, 2018

This information was published 12/11/2018 at 6:59 AM.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast.


The Bottom Line

Wind slabs mostly formed late last week have been slow to stabilize but are trending towards stability. Heightened avalanche conditions remain on specific terrain features, where areas of relatively soft wind slab are possible to human trigger. Additionally, it’s worth continuing to respect the larger, though unlikely to avalanche, hard wind slabs in our terrain. Deeper instabilities do not seem to be a problem at the present time. All forecast areas have MODERATE avalanche danger. Evaluate snow and terrain carefully to identify features of concern. Be on the lookout for areas of exposed crust which provide travel options avoiding the avalanche problem, but also conditions ripe for a long sliding fall.

2018-12-11 Printable PDF


Mountain Weather

Mostly clear skies, temperatures in the single digits, and decreasing wind yesterday had minimal effect on our snowpack structure. Cloud cover should increase through today bringing a possible trace to two inches of snowfall late tonight. Temperatures will warm a few degrees but remain in the low teens on the higher summits. The current west wind of 30 mph on the summit may decrease by late today before increasing tonight. Tomorrow is forecast to trend towards clear skies as the weak low pressure system bringing a chance of snow passes, with wind shifting to the north and increasing to around 50 mph.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Mostly clear skies, temperatures in the single digits, and decreasing wind yesterday had minimal effect on our snowpack structure. Cloud cover should increase through today bringing a possible trace to two inches of snowfall late tonight. Temperatures will warm a few degrees but remain in the low teens on the higher summits. The current west wind of 30 mph on the summit may decrease by late today before increasing tonight. Tomorrow is forecast to trend towards clear skies as the weak low pressure system bringing a chance of snow passes, with wind shifting to the north and increasing to around 50 mph.

  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.

Forecast Discussion

Spatial variability continues to be the name of the game for our upper snowpack, with a slow trend towards more stable conditions due to cold temperatures. In the alpine and on the generally eastern half of the compass rose, hard (1F) stubborn wind slabs are most widespread, with pockets and some larger areas of softer (4F-F) wind slab which remain touchy. Areas of the 12/3 melt-freeze crust are also exposed or nearly exposed at the surface. More westerly aspects, as well as lower elevations, have a far more isolated distribution of any sort of wind slab. Bonding to the crust has been good, limiting our stability concerns around it for the time being. Snow is similarly sticking well to the crust where it’s exposed at the surface, making it appear bright white rather than a more typical grey. Until you’re quite close, it can be challenging to visually determine distribution of our varying snow surface types. Savvy travelers should be able to manage the current avalanche problem through careful evaluation and terrain selection.

Please Remember:

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 12/11/2018 at 6:59 AM.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest