Avalanche Forecast for Wednesday, January 30, 2019
This information was published 01/30/2019 at 7:11 AM.
The Bottom Line
CONSIDERABLE avalanche danger exists on all aspects of mid and upper elevation slopes today with increasing danger due to larger, natural wind slab avalanches in east facing, mid-elevation slopes such as the Headwall of Tuckerman Ravine and the Main Gully in Gulf of Slides. Human-triggered avalanches are likely on all aspects of steep, wind-sheltered slopes. Wind today will increase the likelihood and size of avalanches, especially on leeward, north and east facing terrain, though cross-loading will make travel everywhere tricky. Storm slabs can be avoided in lower angled terrain but be increasingly cautious as slope angles steepen over 30 degrees. Trees and boulders will not have an anchoring effect on the touchy soft storm and wind slabs today.
A fast moving storm deposited 10” of 10% density snow on moderate southeast wind which reached 48 mph overnight. Since then, the wind has diminished to the current 30 mph remaining from the southeast. The heaviest snowfall should be over by around dawn though upslope snow showers will drop another couple of inches through the day, impeding visibility in the process. The well publicized cold temperatures begin to arrive mid-day as a cold front arrives. Wind will shift west and increase in speed to the 50-70 mph range by noon and even higher later in the day and overnight. Upslope snow showers may increase in intensity with the frontal passage with a couple more inches of snow falling tonight. Temperatures will reach down to around -27F, far from the record of -47F set in January, 1934.
Primary Avalanche Problem – Wind Slab
The bullseye information for the growing natural avalanche danger will be the wind shift to the west. Wind will increase and blow snow into thick wind slabs in our largest east facing terrain, creating the possibility of natural avalanches. These wind slabs may be touchy and very sensitive to a human trigger as they are developing today.
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.
Secondary Avalanche Problem – Storm Slab
The new snow fell as temperatures warmed overnight, resulting in a denser and more cohesive snow over lighter, softer snow. While not particularly thick, storm slabs today could still carry you, particularly in areas with an icy bed surface which would be really hard to arrest a slide on. Cracks shooting through the snow ahead of and beside you are a warning sign that the snow is touchy and will likely avalanche.
What is a Storm Slab Avalanche?
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
Firm wind slabs under today’s growing wind slabs may contribute volumes of snow to what may already be a large avalanche in the new snow. The failure layer in today’s avalanche problem will be within the new snow which fell early on but don’t discount a moving mass of snow to trigger something larger in the existing firm wind slabs and piles of sluff debris that exist below steep terrain features. The bullet hard refrozen ice crust beneath the new snow isn’t the best bonding surface for the snow and wind slabs which developed earlier this week. Expect a return to the firm and stubborn but consequential wind slab avalanche problem tomorrow as wind rages overnight.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 01/30/2019 at 7:11 AM.
USDA Forest Service
White Mountain National Forest