Snowpack and Avalanche Information for Monday, May 18, 2020
This information was published 05/18/2020 at 8:18 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Four consecutive days above freezing at all elevations, and a stable weather pattern this week reduces concerns for new snow avalanche problem types, but increases concerns for springtime snowpack hazards. Warm days and cold nights, at least through mid-week, create conditions for a dynamic snowpack that changes by the hour. Be aware of temperature: refrozen snow in the morning will be firm, with long sliding falls possible, and as temperatures rise melting snow at the surface will weaken as it becomes wet or slushy with loose-wet sluff avalanches a rising concern. Generally small in size, sluff avalanches have the ability to entrain skis and carry a person over a cliff or into glide cracks that are now beginning to open up.
As days above freezing stack up, springtime hazards emerge while the snowpack shrinks. Review the objective hazards listed in the Forecast Discussion below and keep these in mind as you plan your day. With some thought on timing and route selection up and down, all of these hazards are avoidable.
MWAC has moved to a Snowpack and Avalanche Information bulletin (known in prior years as a General Bulletin) until the end of the season. Snowpack and Avalanche Information is issued when unstable snow may exist within our forecast areas but after 5-scale avalanche forecasts have stopped. Please remember that avalanches can and do occur after 5-scale avalanche forecasts have ceased!
Tuckerman Ravine, Huntington Ravine and the Gulf of Slides will remain closed to all use until May 31 and possibly later as winter conditions and deep snow remain.
On March 30th, the USFS MWAC took a tactical pause in forecasting operations. Since that time, forecasting and closure monitoring have continued, though forecasts were sent directly to local mountain rescue organizations only. As the public continues to recreate and winter conditions persist in the mountains, it is apparent that current snowpack and avalanche information could be helpful in reducing risks.
Please realize that volunteer rescue resources are currently limited due to concerns about community spread of the coronavirus.
Above freezing temperatures during the day, refreezing at night and light winds are forecast for the next few days. Except for a slight chance of rain early on Monday, no precipitation is expected through at least Wednesday.
Despite the date on the calendar, new snowfall and winter conditions are possible during any month of the year at higher elevations in the Presidential Range. Spring and early summer bring rapid changes to our upper snowpack, with conditions often changing by the hour. Plan accordingly for these changes by reading the weather forecast before you head out (MWObs Higher Summits and NWS Hourly forecast).
One tool to help reduce the chance for unwelcome surprises is the hourly weather information produced by MWObs summit staff. The NWS displays the hourly data going back 7 days here.
Melting snow will be the main factor for snowpack problems over the next several days. The 20” of new snow last week has had 4 days of above freezing temperatures, an inch of rain and has stabilized as we continue towards an isothermal snowpack of generally clear weather, warm days and cool nights. This daily melt-freeze cycle creates the large grained round crystals we know as “corn snow” which will be stable at night and in the early morning when free water is refrozen, but as the day warms melting water percolates through the snowpack dissolving bonds between the crystals, decreasing the strength of the snowpack. Boot penetration is a good indicator of how much loose snow is available for a wet loose sluff avalanche.
As the snowpack melts and recedes, mountain hazards become a significant problem to be aware of. Keep the following spring mountain hazards in mind as you make terrain decisions:
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 05/18/2020 at 8:18 AM.
USDA Forest Service
White Mountain National Forest
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