Avalanche Forecast for Thursday, January 9, 2020
This information was published 01/09/2020 at 7:00 AM.
The Bottom Line
- Avoid the steepest terrain in ravines like the Gulf of Slides, Tuckerman and Huntington Ravines where wind deposited snow has accumulated
- Avoid open areas on and below steep slopes and gullies
- Low visibility will make it difficult to tell whether the slope above you is wind loaded or wind scoured
Natural avalanches remain possible until wind loading stops. These avalanches could be large and could occur without warning due to snow continuing to blow onto the slope above you. Human triggered slab avalanches will remain likely today even after the wind calms. These slabs may break above you and will be thick enough in many areas to contain the snow necessary to carry you into rocks, over cliffs or bury you. If you attempt to ski or climb today in or near avalanche terrain, stay on low angle slopes, avoid the bases of cliffs or leeward areas where drifting snow has accumulated and do not linger in avalanche paths. Avalanche danger is CONSIDERABLE today.
A college group of 5 was involved in a human triggered avalanche descending from the summit yesterday afternoon when they attempted to avoid deep snow on the return trip down the Lionhead Winter Route by taking the Alpine Garden Trail around the northern edge of Tuckerman Ravine. 3 of the 5 were carried by the avalanche, in low visibility, likely down Sluice. Thankfully no injuries occurred, though blind luck was the only contributing factor in the group’s survival.
Steady light snow and snow squalls yesterday produced just over 5” of new snow in the Presidential Range yesterday and around 14” in the past 5 days. Wind increased in the early afternoon and blew from the west-northwest at an ideal speed for moving snow into the larger avalanche paths in the range. Expect cold temperatures today; 8F in the parking lot, around 0F near the base of east facing ravines and -10F on the summit. The temperature will rise to around 5F on the summit as the wind diminishes through the day.
Primary Avalanche Problem – Wind Slab
Wind deposited slabs of snow have been deposited in east facing terrain for the past several days. Several layers of softer, weaker snow sit beneath these layers with an icy and hard surface below that. Cold temperatures since the most recent snowfall and wind loading have not encouraged bonding and settlement. A variety of sizes of avalanches are possible today though none of them could be considered harmless or small in most loaded terrain.
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.
Today is a good day to consider the consequences of travel in avalanche terrain and to place a higher value on the red flags that are waving than the feeling that you must get after it. Many human factors may be at work in your group today. Certainly I feel the looming threat of an incoming mixed precipitation event this weekend and likely many other riders do as well. A moderate result in a stability test performed today could be, and often is, interpreted with a shrug of the shoulders and bias towards a “go” signal. The reality is that stability tests are really not that helpful when assessing wind slabs.
Much better calculus for making a decision exists than any snow pit test could indicate. Reasons for this include multiple weak layers and interfaces are located at random depths scattered around multiple aspects (north-ish through south-ish) all resting on an ice crust that is resistant to bonding and may be driving a faceting process which is also spatially variable. The strength of these slabs is often impressive and can “bridge” across terrain by supporting itself on gully walls or against lower angled terrain below. But sometimes that bridging power, and the bonds that create it, fails under the slightest stress of new snow or a passing skier or hiker, often quite far from the point of fracture.
Like any experiment or study, if you set out looking for some result, you will convince yourself that you have found it. Perhaps you’ll want to avoid this confirmation bias today and consider the obvious signs of recent or continued wind loading and recent avalanche activity. The feeling of scarcity that may be creeping into your decision matrix can be suppressed with the knowledge that it is only early January with lots more winter and good riding conditions yet to come.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. New snow has improved conditions greatly and make these attractive options given the avalanche risk above.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.
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 01/09/2020 at 7:00 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest