This information was published 04/12/2020 at 7:32 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Human triggered avalanches are possible today that could be very large, primarily in east facing ravines. Good visibility will assist in your ability to assess a slope from a distance to identify wind loaded slopes. Keep an eye out for warming today as an added stress on the snowpack. Moist snow is a sign that the snowpack is destabilizing, and the likelihood of a human triggered avalanche is increasing. Avalanche danger today is MODERATE.
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 summit recorded light snow showers and blowing snow on W and WNW wind every hour until 9pm then blowing snow continued through the night and wind speeds dropped. Snow showers totaled 2.6” at the summit with a high temperature of 14F. Harvard Cabin had no measurable new snow and a high of 29F. It’s worth noting that the summit recorded a 117 mph gust early in the day, and wind remained in the 70-80 mph range for most of the day.
Today, we should see more sun than clouds with temperatures on the summit rising to the upper 20sF, and likely above freezing at ravine level. Aspects that receive the most direct sun may see temperatures well above freezing. West wind today will be in the 30 to 45 mph range.
Tomorrow brings mixed precipitation and rain as temperatures rise above freezing at all elevations with over an 1” rain forecast. South and SW wind is expected to increase sharply in the morning hours to 80-100 mph with higher gusts in the afternoon, likely coinciding with the heaviest rainfall.
Primary Avalanche Problem – Wind Slab
Wind slabs formed from the 23” of recent snow were affected by extreme winds and likely stubborn to a human trigger, though should command respect due to the possibility of producing a very large avalanche, especially in locations that did not avalanche naturally during the storm cycle. The largest wind slabs will be found primarily in east facing terrain with the greatest fetch: Tuckerman Ravine and the Gulf of Slides. Warming should also be on your radar as rising temperatures and solar radiation will work to destabilize the snowpack. Temperatures may not warm enough to produce the obvious tells, such as roller balls, so keeping an eye out for subtle wetting of the snow surface can clue you to warming as a red flag.
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.
Current avalanche forecasts are being produced for SAR teams to give you an idea of what you’ll find. Due to the current situation, MWAC is spending less time in the field than in a normal April, leading to a degree of uncertainty into today’s forecast, particularly in terms of distribution due to possible wind scouring and avalanche cycles.
Poor visibility over the last few days has hampered our ability to get field observations, leading to some uncertainty on size and sensitivity.
Normally well traveled hiking trails and ski trails in the Cutler River Drainage have had no human traffic after this past storm. Expect difficult travel conditions that will require snowshoes nearly everywhere until the snow settles.
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.
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 04/12/2020 at 7:32 AM.
USDA Forest Service
White Mountain National Forest
Sign up to get the daily MWAC avalanche forecast in your inbox