This information was published 04/28/2020 at 7:02 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
New wind slabs are possible to avalanche from a human trigger today that could be large in locations downwind of E, and NE wind. While many suspect slopes for today’s avalanche problem have limited upwind fetch available for snow transport into slabs, up to 19” of new snow over the last 48 hours suggests large, dangerous wind slabs could be found; travel cautiously in avalanche terrain until you can determine otherwise. Avalanche danger today is MODERATE.
Yesterday, snow continued with snow recorded every hour on the summit until midnight. Wind at 70-80 mph started the day in the E and slowly shifted to the ENE then NE. Temperatures on the summit remained in the teens F.
Summit new snow: 3.1” (0.37” SWE). 48H storm total: 4”. Harvard Cabin new snow: 6.3” (0.69” SWE). 48H storm total: 13.3” Gray Knob new snow: 8.26”. 48H storm total: 19.3”
Today, cloudy skies become clear late. Temperatures in the lower 20sF with N wind at 20-35 mph. Tomorrow begins clear, becoming cloudy with temperatures in the upper 20s F. South east, then S wind at 10-25 mph increases to 25-40mph.
Primary Avalanche Problem – Wind Slab
Wind from the E and NE formed new wind slabs in lee terrain of varying size through middle and upper elevations and are likely stubborn due to wind speeds and snow density. The largest slabs will be found on S, SW and W aspects, while smaller slabs may be found closer to SE and NW aspects due to cross loading. Bullseye locations for this avalanche problem include the northern gullies in the Gulf of Slides, the north and east side of Oaks Gulf, and likely other more remote slopes in the range in the lee of recent NE wind. One factor potentially limiting the size of new slabs is lack of upwind fetch feeding snow transport on the suspect slopes. Conditions today are unfavorable for continued wind loading, limiting or eliminating the chance for natural avalanches to occur.
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.
Consistent wind from the E and NE for the duration of this recent storm positions the wind slab avalanche problem onto slopes different than the usual east facing ravines we often see. Storm totals and upwind fetch were the heated topics in the Forecaster’s meeting this morning. Storm totals varied from 4” on the summit to 19” at Gray Knob which suggests less snow at upper elevations available for wind slab formation, or simply that the wind direction is less favorable for collecting snow on the summit. This, combined with less than ideal upwind topography for collecting transportable snow results in a moderate degree of uncertainty on just how large the wind slabs will be today.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
The Lion Head Winter Route remains the easiest route to the summit from Pinkham Notch but requires an ice axe, crampons (not just micro-spikes) and possibly a rope. This is a mountaineering route and requires solid skills for a safe, timely ascent.
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.
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 04/28/2020 at 7:02 AM.
USDA Forest Service
White Mountain National Forest
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