This information was published 04/22/2019 at 6:59 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Wet avalanches and springtime hazards will present equal danger to those traveling in avalanche terrain today. Wet loose avalanches, commonly known as sluffs to skiers and riders, will be possible to initiate in steep terrain, but can easily be managed by moving to the side and letting debris pass. The outside threat of a wet slab, while unlikely, makes lingering under avalanche paths a poor choice. All forecast areas have LOW avalanche danger. Holes where the snowpack in undermined by flowing water, both obvious ones and others that may open today, horizontal glide cracks near cliffs, and falling ice and rock will further complicate travel. Many of these spring hazards can be avoided by travel management, particularly if you can see where the hazards will present themselves.
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After a wet weekend, today looks like we’ll get a break, though the April showers weather pattern will likely continue this week. High temperatures yesterday were 45F on the Summit and 50F at Hermit Lake. Rain in the morning produced 0.21”. Today, light wind from the SE may increase to 20mph from the NE this evening. Fog interspersed with sunshine to start the day will give way to increasing clouds. Rain should hold off until the evening hours, with up to ¼” arriving tonight. Mostly cloudy skies with possible rain Tuesday will give way to a chance of below freezing temperatures overnight tomorrow.
Primary Avalanche Problem – Wet Loose
Wet loose avalanches will be small and slow moving. These are likely to be caused by skier induced sluff and can be managed by waiting off to the side and letting this sluff move downhill first. Such sluffs are often small enough that they won’t bury you, but could easily carry a person towards other hazards like an opening glide crack or over an ice bulge if they catch you unaware.
What is a Wet Loose Avalanche?
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Secondary Avalanche Problem – Wet Slab
The wet slabs that remain a relevant avalanche problem are largely driven by our concerns of significant water running under the snowpack. A thorough soaking of the snowpack this past weekend penetrated deep into the snow and likely stabilized most deep layers of concern. Today’s weather will continue to drive warmth into the snow, but we are likely close to a fully isothermal snowpack, making deeply buried weak layers less likely to drive a wet slab.
What is a Wet Slab Avalanche?
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
For those who have not had eyes on the snowpack since last week, expect to see major changes the next time you visit. Falling apart or shrinking rapidly are accurate ways to describe what’s currently going on in avalanche terrain. Springtime hazards are appearing and the following should be discussed equally with avalanche hazards today:
Opening creeks and streams
Holes near trees, rocks, and cliffs
Undermined snow that could easily collapse
Glide cracks on wide open snow slopes
We believe the time of rapid change has passed and the snowpack is becoming more stable. That being said, the weather pattern we are currently experiencing (above freezing temperatures since Thursday evening) could be described as a little weird. Weird weather has the potential to create weird avalanches. A freeze will help, but a solid freeze looks far off at the moment. All this indicates the snowpack is trending toward stable, but the time to let your guard down has not yet arrived.
The Sherburne and Gulf of Slides ski trails are deteriorating quickly. Expect water crossing to be the big challenge, along with bare patches, exposed rocks, and ice.
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 04/22/2019 at 6:59 AM.
USDA Forest Service
White Mountain National Forest
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