Avalanche Forecast for Tuesday, March 24, 2020
This information was published 03/24/2020 at 6:58 AM.
The Bottom Line
Dangerous avalanche conditions exist today thanks to significant snowfall yesterday and increasing wind today. Human triggered avalanches are likely today as storm slabs are widespread in the terrain. As wind increases, be on the lookout for developing wind slabs that could possibly avalanche naturally. Conditions in the mountains have dramatically changed in the past 24 hours: if you do not carry avalanche rescue gear, you do not belong in avalanche terrain today. Even with the new snow, the icy surface is lurking underneath and crampons and an ice axe may be useful for gaining elevation. Avalanche danger today is CONSIDERABLE. Conservative decision-making is essential.
Yesterday started with temperatures in the single digits on the summit and wind from the S in the 30-40mph range. Snowfall began in the morning, but really picked up in intensity mid-afternoon, producing over 8” on the summit. During the course of the day and overnight, temperatures warmed to the current 20F on the summit while wind stayed form the S and slowed to 15mph.
Today, wind has already shifted from the S to the NW and will continue to shift to the N. Speeds will increase from the overnight 20-30mph to 35-50mph later. Temperatures should fall slightly through the day. While the bulk of the system has passed, lingering moisture around the mountains could produce another 2” today.
Tomorrow will be warmer than today, though it should stay below freezing at mid and upper elevations. Wind will shift to the S Tuesday night and then back to the N on Wednesday. Flurries may produce an inch of snow tomorrow.
Primary Avalanche Problem – Storm Slab
As of 6am, the summit has recorded 8.3” of snow. This fell as temperatures increased, likely creating an upside down storm slab on all terrain. This slab sits on a bed surface consisting of an icy melt/freeze crust. Careful snowpack evaluation should be done before committing to steep terrain with this snow, looking at the cohesiveness of the slab and its ability to propagate. Storm slabs like the ones found in avalanche terrain today are not common on Mt. Washington and have a history of fooling skiers who are used to looking for obvious layers formed by wind. Layers formed by fluctuations in temperature are often thin with very slight variations in density that can be difficult to observe directly. Watch for shooting cracks or whumphing today on lower angled terrain as clues for what could take place on steeper slopes.
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.
Secondary Avalanche Problem – Wind Slab
Wind transport of the snow will increase as wind speeds increase today. As speeds should remain under 50mph, wind slabs may be reactive and are likely to fail under the weight of a skier or possibly even naturally avalanche as storm slabs morph into wind slabs and the strength of the weak layer gets overwhelmed.
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.
If you’re heading skiing today, please include a discussion of the human factor with your partner and beware of powder fever. In addition to the snowpack keeping skiing less than fun the past week, we’ve all toned it down and have practiced keeping our distance. Today will change that and it’s likely people will flock to the hills. Look around to the rest of the country for examples of how skiers either helped themselves by acting responsibly or hurt their cause by ignoring global advice and crowding the backcountry. All ski areas have closed operations and many are closed to all use, including those looking to earn their turns. Please do your homework before showing up to a ski area and assuming you can use their land.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
The Lion Head Winter Route remains the easiest route to the summit from Pinkham Notch but requires an ice axe, crampons (not just micro-spikes) and possibly a rope. This is a mountaineering route and requires solid skills for a safe, timely ascent.
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 03/24/2020 at 6:58 AM.
USDA Forest Service
White Mountain National Forest