This information was published 04/23/2019 at 6:56 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Many spring hazards are becoming prevalent in our terrain, and should keep you on your toes today along with unlikely but not impossible wet slab avalanches. Wet loose sluff avalanches initiating under your skis or board could easily pull you towards a number of growing hazards if not managed appropriately. Avalanche danger is LOWtoday. Many glide cracks or crevasses, holes melted by flowing water, and areas of undermined snow continue to develop and combine with the icefall and rockfall potential that are typical in of period of warming. A lucky skier had a very close call yesterday, falling into one of these deep melted out holes in the Headwall of Tuckerman Ravine. After 20 minutes of extreme effort while becoming dangerously wet and cold, the experienced backcountry skier was able to climb out via another connected hole. A similar fall into the many holes that are harder to escape would not have ended so well and should remind us all to respect this significant hazard.
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Yesterday brought our streak of days without a refreeze to five, with a low of 33F and a high of 42F on the summit of Mount Washington. Rainfall overnight has totaled 0.21” and should end this morning as mostly cloudy skies give way to rain again tonight. High temperatures will be in the mid to upper 40’sF with tonight remaining above freezing. Variable wind today should become westerly and increase tonight and into tomorrow, as precipitation tapers off but continues through the day. Temperatures will drop and possibly result in mixed precipitation and somewhat of a snowpack refreeze at upper elevations.
Primary Avalanche Problem – Wet Loose
Wet loose sluff avalanches are possible to initiate under your skis or board in all steep terrain and likely on slopes that have seen minimal recent ski traffic. While typically not large enough to bury a person, these heavy sluffs can easily knock you off your feet and cause an unwanted fall in high consequence terrain. Be ready to manage sluff in any steep terrain.
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
Wet slab avalanches releasing naturally are unlikely but remain a concern in steep terrain where water is flowing under the snow. Identify the runout zones that could be threatened by a large wet slab and minimize your time in these areas.
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.
The most recent winter storm was just one week ago, but the entire Presidential Range has since spent five full days above freezing. It’s a good time to remember that such extended warming is not the norm on the higher summits. Heat and moisture are penetrating deep into our snowpack. Wet slab avalanches are tricky to predict in more normal warming conditions, so the current abnormal weather lends additional uncertainty to their likelihood. The opening of many glide cracks suggests cohesion through the full depth of our snowpack. That said, wet slab avalanches can release at or near the ground, especially when significant water is flowing as it is currently. It’s worth minimizing your time in avalanche paths to manage this low probability but high consequence hazard, and also being mindful that the warming conditions are making our typical spring hazards quite prominent:
Holes near trees, rocks, and cliffs
Undermined snow that could easily collapse
Glide cracks on snow slopes
Falling ice and rock
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 04/23/2019 at 6:56 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
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