Avalanche Forecast for Sunday, March 1, 2020
This information was published 03/01/2020 at 6:41 AM.
The Bottom Line
Evaluate snow and terrain carefully today for the presence of wind slabs, some of which may be reactive to a human trigger and large enough to bury a person. Consider traveling on the firmer, scoured snow to avoid these wind slabs while reducing your exposure to overhead hazards such as other people triggering an avalanche on you. Avalanche danger is MODERATE today. Natural avalanches are unlikely but human triggered avalanches remain possible.
Yesterday, upslope snowfall continued off and on through the day ultimately adding another 1.5” to the 2” which fell on Friday. Peak gusts on the summit hit 74mph from the NW though winds were generally moderate most of the day.
Today, seasonably cold temperatures continue with wind diminishing further. Expect a high just above 0F with NW winds around 30-40mph on the summit. Summit fog and clouds should clear out by midday.
Tomorrow, high pressure will make way for another warm disturbance which may bring some rain to the forecast area. The freeze line is uncertain at this time but some rain seems likely at middle and lower elevations.
Primary Avalanche Problem – Wind Slab
Wind slabs should be on your radar today. Gusty and shifting winds over the past 48 hours have deposited the upslope snowfall in a patchwork of wind slabs over firm, challky snow. These slabs may be large on lee slopes and gullies downwind of a large fetch such as the Headwall of Tuckerman Ravine and across the Gulf of Slides. If you are on a slope over 30 degrees and see cracks shooting ahead in the snow or the snow is over your boot-tops, your risk of triggering a dangerous avalanche has increased substantially.
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.
Low visibility persisted yesterday with few observations from our forecast area though observations from Huntington and Gulf of Slides indicate that a patchwork of soft snow, firm and chalky snow, and some exposed ice crust is the norm. Wind sheltered areas low in east facing bowls provided some soft powder skiing yesterday and likely will today as well. Wind and more snow showers overnight likely refreshed some slopes but also may have made some of the pre-existing slabs thicker and possibly more dangerous. Ease into the terrain and bring a strong partner or partners. We’ve received no observations from the west but loading there seems likely to have occurred during the east winds the blew early in the storm last Thursday.
The Sherburne and Gulf of Slides ski trails are covered with soft snow 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 03/01/2020 at 6:41 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest