Avalanche Forecast for Sunday, January 13, 2019
This information was published 01/13/2019 at 6:56 AM.
The Bottom Line
High wind speeds have deposited wind slabs that will be stubborn to human triggers today, but could produce a large avalanche. Hard wind slabs like those that exist in much of our terrain are difficult to evaluate for stability, but can be easily navigated by avoidance. Today’s avalanche problem often produces no avalanches until an unlucky skier or climber ventures to find the particular weak spot in the slab. The potential size and destructiveness of an avalanche today is keeping our danger ratings elevated at MODERATE. Locations with a LOW rating (Tuckerman’s Left Side and Boott Spur as well as Huntington’s Northern Gullies) do contain snow that could produce an avalanche and will still require careful terrain selection.
The last recorded snowfall in our terrain was Thursday evening. Since that time, NW winds blew in the 70-100 mph range until midday yesterday. A sharp drop in wind speed took place overnight with wind currently WNW 15mph. Today, wind will be light and variable with some high level clouds. Expect sunshine for much of the day with temperatures on the summits cresting at 10F. No new snow is forecast tonight or tomorrow.
Primary Avalanche Problem – Wind Slab
Wind slab exists primarily on the eastern half of the compass. Most of these formed on high wind speeds after a widespread avalanche cycle Wednesday night and Thursday. Most existing wind slabs will be stubborn to human triggers. Areas with a large upwind fetch at mid-elevations have the potential to produce a large avalanche should you find the thin spot of the slab. Lower elevations or wind-sheltered locations may harbor softer pockets of wind slab that may be possible to produce an avalanche, but the overall size will be smaller.
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.
The effect of Mount Washington’s notorious wind combined with last week’s 26” of snow should finally reveal itself today as blowing snow and fog finally subside. Ravines with a larger upwind fetch such as Tuckerman and the Gulf of Slides both saw significant avalanche activity, likely Wednesday into Thursday, while other ravines with a similar aspect but smaller fetch saw much less loading of wind transported snow. Wind slabs that remain in east-facing terrain will be variable in size and distribution due to terrain, the timing of recent avalanche cycles, and reloading. Making good observations of distribution while moving in the field and basing travel decisions off this will go much further than conducting stability tests while in the avalanche problem today.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. Thanks to those who submitted observations on our website. These are invaluable to the avalanche center and we hope to see more submissions as the season progresses.
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 01/13/2019 at 6:56 AM.
USDA Forest Service
White Mountain National Forest