Avalanche Advisory for Monday, February 26, 2018

This advisory expires at Midnight.

Huntington will have CONSIDERABLE and MODERATE avalanche danger today. Central, Pinnacle, Odell, South, and Escape Hatch have Considerable danger. Natural avalanches are possible and human-triggered avalanche are likely. North, Damnation, and Yale have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features.

Tuckerman Ravine will have CONSIDERABLE avalanche danger today. Dangerous avalanche conditions exist. Natural avalanches are possible and human-triggered avalanche are likely. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential.

AVALANCHE PROBLEM: Today’s avalanche problem is wind slab. This hazard will increase slowly through the day as wind continues to transport snow from the fetch into avalanche terrain. Areas of largest concern are those in the direct lee of W and NW wind as those will see the most loading today. Also of concern would be gullies that were in the lee of yesterday’s S and SE wind. Areas rated Moderate today had less developed bed-surfaces prior to yesterday.

WEATHER: Snowfall began Sunday around 8:30am when the Summit was recording a temperature of 7F and SE wind with speeds around 35mph. As the day progressed, temperatures warmed to the high-teens and wind shifted S with speeds increasing by about 10mph. A period of freezing drizzle was observed during the last hour of precipitation in the late afternoon. Total accumulation on the Summit was 5” of snow with a snow water equivalent of 0.56” while Hermit Lake recorded 2.4” of snow with a SWE of 0.47”. Today, temperature will fall from the teens into single digits and wind will shift to the NW and stay in the 50-70mph range. We may also see up to 2” of upslope snow arrive through the day.

SNOWPACK: Before snowfall began yesterday, our refrozen snowpack posed no avalanche concerns. Rather, that hard, icy snow will now provide a slick bed surface for developing wind slab. Wind slab that began forming yesterday and will continue to develop today will likely have an upside-down structure due to warming temperatures as snow arrived. With wind shifting from SE yesterday all the way to NW later today, multiple aspects will see direct loading as well as cross-loading. Visibility into avalanche terrain this morning is minimal, but enough to see signs of wind transport as well as scattered areas of old surface low in avalanche paths. This leads us to believe that the combination of wind speed and snow density will generate greatest wind slab development high in start zones. As visibility may prevent seeing these start zones, it may be hard to evaluate this from a safe distance. Also keep in mind that several gullies with a northerly aspect that we do not forecast may have significant wind slab development and potentially could run into or across other slide paths. This is particularly true on the Boott Spur ridge.

• Safe travel in avalanche terrain requires training and experience. This advisory 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.
• Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or Harvard Cabin.
• Posted 8:00 a.m., Monday, February 26, 2018. A new advisory will be issued tomorrow.

Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856