Avalanche Forecast for Saturday, January 4, 2020
This information was published 01/04/2020 at 7:38 AM.
The Bottom Line
- Large natural avalanches or human triggered avalanches occurred two-three days ago.
- An icy bed surface and weak layers beneath the existing wind slab may not have fully healed and bonded.
- Evaluate snow and terrain carefully. Smooth, hollow or stiff snow on rollovers and in the steepest terrain should be avoided or carefully assessed.
- New snow falling today and summit fog will make visual assessment difficult.
- Human triggered avalanches capable of burying a person remain possible in specific areas. Natural avalanches are unlikely.
The Lion Head Winter Route is open and remains the safer choice for accessing the summit of Mount Washington from the east. An ice axe and crampons are needed near treeline and above with micro-spikes useful on trails below.
This forecast is the first 5-Scale daily avalanche forecast of the 2019-20 season for reasons explained here. Thank you to our community for your support and patience!
Temperatures have slowly risen into the mid and upper 20’s since the last storm dumped over a foot of snow in the high country. A low pressure system passing to our south will bring up to 4” of new snow as the system passes, with and inch or two expected during daylight hours. West wind will decrease through the day though may blow hard enough at times early on to move some snow. Expect visibility to be challenged by snow, flat light and building summit fog. Wind will diminish from the 40mph range to the 15-30mph range today. Expect more snow and increasing west winds overnight with colder temperatures and stronger winds tomorrow more than likely building new wind slabs tomorrow.
Primary Avalanche Problem – Wind Slab
Dense snow from the New Years storm followed by more lower density snow on strong west and northwest wind built wind slabs on lee slopes and wind sheltered locations. Cross-loading also occurred along with pooling in the aprons beneath steep slopes, gullies and cliff bands.
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.
Sixteen inches (42.6cm) of snow was recorded at Hermit Lake during the New Year’s storm. This snow was dense, in the 15-17% range, early on in the storm before upslope snow fell in the wake of the storm. That snow was a mix of rimed snowflakes, a.k.a. graupel, and somewhat lower density snow that was easily transported by increasing westerly winds in the 60-80 mph range. A natural avalanche cycle seems to have occurred mid-storm though did not to be particularly widespread. The next clear day, Thursday, brought folks out to ski on the newly refreshed slopes and gullies with two avalanche incidents resulting. Two skiers approaching Left Gully were wisely spread out and hugging the bushes on the left side of the floor of the Ravine when the first avalanche occurred. Unfortunately they were not quite far enough out of the avalanche path for one of them to avoid being swept by the debris. That avalanche seems likely to have been a natural avalanche though wind slabs can be triggered from thin spots in the slab and from below. In any case, traveling beneath recently loaded slopes is a roll of the proverbial dice. The second avalanche was triggered by an 18 year old solo male skier with no training or avalanche rescue gear ascending what he believed to be Right Gully. Details are limited but he triggered the concave bowl beneath Sluice and was carried towards Lunch Rocks by a fairly large avalanche in the D2 range.
As of Friday, the New Year’s storm and wind loaded snow that followed contain layers that fail in the moderate range and display some tendency to propagate in stability tests. Though slowly warming temperatures have encouraged a healthy degree of settlement, the rounding and sintering that needs to occur in the angular grains deeper in the snowpack may not have occurred yet. Given the icy bed surface, steep slopes with large areas of hangfire, combined with the recency of avalanche activity (less than 48 hours as of this writing) and potential for some new snow makes it hard to rule out human triggered avalanches today.
There has been only one observation and no reported avalanches from the lower elevation areas in Crawford Notch though wind transported snow during and after the storm indicate that caution is advised there.
Gulf Of Slides Observation 1/3/20
Conditions on the Sherburne ski trail have improved with the recent snowfall though some rocks and open water bars remain.
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 01/04/2020 at 7:38 AM.
USDA Forest Service
White Mountain National Forest