This information was published 04/10/2020 at 7:00 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Dangerous avalanche conditions exist today with large natural avalanches likely. Conservative decision-making and cautious route-finding will help those performing search and rescue operations stay safe. Avalanche danger is HIGH due to the likelihood and potential size of avalanches today. Assess wind-loaded slopes and runouts from afar and decide as a team which areas are off-limits. East-facing slopes with a large fetch, primarily Tuckerman Ravine and the Gulf of Slides, have the potential to produce very destructive natural avalanches and would be some of the areas best dealt by avoidance. Some slopes may have already avalanched. These slopes will reload and may still naturally avalanche again, but would produce a less destructive avalanche. In addition to avalanche hazard today, be aware of holes in the snowpack that have been covered with the new snow as well as the potential for a sliding fall on wind-scoured slopes. PPE today includes avalanche rescue gear, crampons and an ice axe, as well as what you need to deal with close contact with other people.
Rescuers should respond with a surgical mask or high quality homemade mask for themselves along with hand sanitizer and/or wipes. Due to wide community spread of the virus, every patient and rescuer may be a coronavirus carrier so act accordingly. In the Cutler River Drainage, we have an extremely limited supply of N95 masks which will be reserved for USFS staff and the patient. As always, rescuers will be turned away without this and other PPE, including beacon, shovel and probe.
Yesterday, the mountains received significant snowfall that continued through the night. So far, MWObs has recorded 12.2” (15” at Harvard Cabin) of snow with a SWE of 1.74”. The first half of this snow arrived on SE wind 30-50mph when temperatures were in the 20sF. Around 9pm yesterday, wind shifted to the WNW and increased to around 80mph. Temperatures also dropped into the teens F around this time.
Today will produce more snow for the summits, possibly up to 3” with the heaviest snow falling early PM. Wind will be from the WNW 60-80mph for the day.
Tomorrow, upslope snow showers may continue, producing up to another inch tonight and possibly again tomorrow. Wind will be 60-80mph from the NW tonight, and decrease slightly tomorrow.
Primary Avalanche Problem – Wind Slab
Over a foot of new snow will get hit by extreme wind today from the NW. Wind slabs have formed, may have already avalanched, and will build again. We may have passed peak instability last night, but large and far-running natural avalanches will remain a concern for the day. The bed surface for today’s avalanche problem is an isothermal snowpack, eliminating deeper concerns. It’s likely many slopes will already have avalanche debris from last night’s cycle. This debris does not indicate the slope is devoid of wind slab as rapid reloading will occur today; this just indicates the size of the avalanche will likely be large (enough to bury a person) rather than very large (enough to damage your truck).
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.
High avalanche danger comes with this travel advice: travel in avalanche terrain is not recommended. As rescuers, we often think we have the obligation to go no matter what. Remember that each member of a team has the ability to raise the safety card and say this doesn’t feel right. Risk management is a game we play and today may be the day where you say no from the get-go as trying to deal with very heads up avalanche conditions in mid-April while you’re not 100% mentally focused may actually do more harm to the team than good. Those who are experienced with avalanche travel will have to step-up today and take a leadership role in the field, recognizing all the various ways to enact a rescue from afar. These may include standing just out of an avalanche path and directing the partner of the victim how to perform a search or slowing way down and exposing one experienced rescuer to the hazard at a time. While travel in avalanche terrain is not recommended at times of High avalanche danger, bear in mind much of avalanche terrain can be avoided by using ridges and aretes that may slow progress, but will provide the necessary access to your victim.
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. Clickhere to check it out.
Recent snowpack and avalanche observations can be foundhere and on Instagram. Your observations help improve our forecast product. Please take a moment andsubmit 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 04/10/2020 at 7:00 AM.
USDA Forest Service
White Mountain National Forest
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