Avalanche Forecast for Wednesday, February 26, 2020
This information was published 02/26/2020 at 7:10 AM.
The Bottom Line
Small avalanches will become possible in isolated areas and extremely steep terrain later today. Keep a close eye on the rate and intensity of new snow and consider the consequences of being knocked off your feet by a small avalanche. While there will be LOW avalanche danger today, many other mountain hazards will persist due to the recent warm weather. Count icefall, rockfall, undermined and poorly bonded ice and a rotten snowpack, among them, especially at mid- and lower-elevations.
Yesterday, temperatures on the summit of Mount Washington hovered around 25 while mid elevation ravines temperatures remained higher. Limited field observations make the refreeze line uncertain though it seems likely to have refrozen at ravine levels overnight. How deep the refreeze remains uncertain as well.
Today, expect summit fog, continued mild temperatures and low wind speeds from the east then south. Snow shower activity today will be hit or miss with a trace to 3” forecast to fall in passing snow showers before heavier precipitation begins this evening. Light rain showers are on tap for lower elevations.
Tomorrow brings an end to our dry spell with a significant low pressure system gaining strength over the Atlantic which will drop a foot or more of heavy snow in higher terrain beginning tonight. Wind will be from the south overnight and then east until late afternoon. Wind will shift west late in the day tomorrow.
Primary Avalanche Problem – Wet Loose
Rain on snow and continued warm temperatures are the driver for this avalanche problem. Generally the snowpack has been warm and wet since Sunday with good settlement. Most of the firm snow prime avalanche paths will likely be stable. That being said, rain on snow and ice is never a good thing for winter recreation. This observation is a good reminder. Loose snow on slabs of ice or rock, especially at lower and mid-elevations should be on your radar.
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 – Wind Slab
New snow showers could bring up to 3” new snow today. Wind will be from the east and south and will be light. Wind slabs should be limited to areas beneath steep terrain where sluffing snow accumulates. If snow depth climbs above your boot-tops and you see shooting cracks, you found the avalanche problem.
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.
Snow and ice conditions will be widely variable by elevation and aspect due to the departure from seasonal average temperatures. Today is likely to be another day where large and deadly icefall could occur, especially in Crawford Notch. More than the usual vigilance regarding your position in the fall line will go a long way today to help keep you out of harm’s way.
Last Sunday, snow rangers assisted a party whose dog took a terrible fall down the Chute. We generally have a policy which discourages diverting rescue resources away from potential human casualties but it proved impossible to watch the dog tomahawking and bouncing down the 50 degree slope and not do something to help. Please remember that dogs love to please their people more than anything in the world and are incapable of assessing risk. That risk assessment is up to you. It is telling that the USFS MWAC’s avalanche rescue dog NEVER goes with us into steep terrain without a harness and rope.
Consider the value of a 30 minute walk before or after your trip to the mountains where sharp ski edges and tumbling falls can send your dog to the vet, or worse.
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 02/26/2020 at 7:10 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest