Avalanche Forecast for Thursday, January 10, 2019
This information was published 01/10/2019 at 7:08 AM.
The Bottom Line
Recent avalanche activity, new snow and wind loading are the red flags that continue to highlight avalanche danger today. It’s likely that natural avalanches occurred overnight in the eastern ravines, which if they haven’t slid yet, they may slide today. Slopes and gullies on the eastern half of the compass rose will continue to be stressed by new snow and wind loading today and are rated CONSIDERABLE. Natural avalanches in these areas may be large and run far into low angled terrain. Limit your exposure to these runouts today, even if these slabs appear to be firm and stubborn. Better yet, enjoy the snow in sheltered low angled glades or trails until new snow and wind slabs have settled and bonded. Be wary of wind drifted snow on slabs of ice or in gullies at lower elevations as well. These areas have a MODERATE danger rating due to the possibility of a human-triggered avalanche.
Around 12” of new snow fell at 3800’ and above yesterday with only slightly less at lower elevations. Initially this storm began with a light easterly wind but as the low passed, the more typical howling northwest wind began, ultimately reaching into the 90’s mph for a three hour period late yesterday afternoon. The wind fell off slowly through the night, reaching the current 55 mph while upslope snow continued, bringing a few more inches to the summits overnight. Another 2-4” is expected to fall today and be driven by strong northwest winds in the 70 mph range. Clouds, fog and blowing snow will reduce visibility through the day. Cold temperatures arrive today as well and will stick around for the weekend with highs in the single digits and lows reaching into the negative teens on Friday night.
Primary Avalanche Problem – Wind Slab
Wind slabs will continue to form today and add stress to the slabs built with the 20+” of snow which fell over the past five days. Look for firm, smooth pillows of snow which may be distributed widely around the terrain due to shifting wind directions and velocity. Recent wind slabs may be stubborn to a human trigger but natural avalanches will continue to be a threat as long as the wind keeps moving snow onto slopes and gullies.
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.
There is little doubt that east facing ravines experienced an avalanche cycle last night but the extent of the activity remains to be seen. In question is the depth of the slabs which may have failed. Prior to yesterday’s storm, unreactive wind slabs a meter or more thick were found in many areas of Tucks and Huntington. Observations and stability tests indicated that they were well bonded to the ice crust or the older firm wind slabs beneath but a large, heavy trigger such as a hand charge, which we don’t have, or a new load of snow may be what’s needed to break them loose. Low visibility and elevated avalanche danger won’t allow many of the missing pieces of the ongoing avalanche puzzle to be put in place today, but you can be sure that the puzzle has changed dramatically since yesterday morning.
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 01/10/2019 at 7:08 AM.
USDA Forest Service
White Mountain National Forest