Avalanche Forecast for Tuesday, February 25, 2020
This information was published 02/25/2020 at 7:24 AM.
The Bottom Line
All forecast areas have LOW avalanche danger today. Use normal caution for avalanche terrain and remember that Low does not mean no avalanche danger.
South facing aspects warmed from the sun over the last two days may be re-frozen in steep terrain creating a sliding fall hazard, requiring crampons and the ability to self arrest to travel safely.
Yesterday was unseasonably warm with clear skies and wind from the west at 35-45 mph. Highs from around the Presidential Range yesterday:
Today warm temperatures continue with summit high temperatures in the upper 20sF. Scattered clouds this morning will thicken through the day limiting/eliminating the effects of the sun on southern aspects. Light precipitation is expected in the afternoon as snow or freezing drizzle with a trace to less than an inch expected. Wind will be from the west at 5-20 mph.
Tomorrow, 1-3” of snow is possible with summit temperatures in the mid 20sF and cloudy skies. Wind from the west at 15-30 mph will increase to 25-40 mph. Avalanche danger will increase if we see snow totals at the upper end of the forecast.
Primary Avalanche Problem – Wind Slab
Cloudy skies today and slightly cooler temperatures will limit the amount of warming the week-old wind slabs at mid and upper elevations will receive today. This should limit or even eliminate the instability concerns due to surface warming experienced over the last two days. What still remains, is a firm wind slab over an ice crust and a thin layer of weak facets. Triggering a wind slab today is unlikely though not impossible should you find a thin spot. With a trace to under an inch of new snow in the forecast, it’s worth keeping an eye out for new wind slab development, though with such little snow and light wind this will be unlikely.
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.
Secondary Avalanche Problem – Wet Loose
Wet loose avalanches are a concern today at mid and lower elevations due to warm temperatures and the chance of precipitation that will fall as rain or freezing rain, depending on elevation. These will likely be small in size, and more likely on steep terrain where even a small avalanche can have consequences.
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.
The Moderate avalanche hazard over the last two days was driven by the warm air temperatures and bright sun working to warm surface snow, weakening the strength of the wind slab. Today, clouds should eliminate solar radiation from the equation, leaving us with ambient air temperature as the primary weather factor affecting snow stability. Today will be warm, but slightly cooler than yesterday, and air temperatures in the mid and upper elevations will likely remain just below freezing through the day. The second weather factor today is the chance of snow or freezing rain. Precip should fall as snow at upper elevations, and likely mid elevations. Lower elevations will see some light rain, which will add some degree of instability to the snowpack. With temperatures hovering around the freezing mark and with little QPF for precip we don’t expect these subtle factors to have a significant effect on the snowpack today.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit 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 02/25/2020 at 7:24 AM.
USDA Forest Service
White Mountain National Forest