Avalanche Advisory for Tuesday, March 27, 2018

Huntington and Tuckerman Ravines have LOW avalanche danger. All forecast areas have Low avalanche danger. Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: A significant warm-up today will make loose wet sluffs the primary avalanche problem on sun exposed aspects. Loose dry sluffs are still possible on steep and shady aspects. We expect these small avalanches which could easily knock you off your feet to occur primarily in the few inches of snow which fell late Saturday and into Sunday. The small and isolated pockets of soft and thicker wind slab which formed from that recent snow could begin to act as a wet slab on south facing slopes and should be on your radar in all terrain. The older, widespread, and hard wind slab that is thinly covered in many areas by the newer snow has been unreactive to human and natural triggers and this trend will likely continue. That said, a significant warming like our sun-exposed slopes will experience today can awaken previously unreactive layers at or near the surface. It’s again a reason that “Low” does not mean “No” avalanche danger, and that travelling one at a time, with your beacon, probe, and shovel, is advisable.

 Also be aware that while the sun will soften some aspects, others will remain hard, and sun softened snow can quickly refreeze with the return of shade. Crampons, ice axe, your ability to use them, and wise terrain choice are all necessary tools to prevent a high consequence long sliding fall. Sun will also warm ice today, making icefall a key overhead hazard to consider and manage.

 WEATHER: Current summit temperature is approaching 20F, already nearing yesterday’s high of 24F and forecast to exceed the freezing mark today. Yesterday’s high of 41F at Hermit Lake will almost certainly be exceeded. Yesterday was warm and spring-like, but today will be our first truly warm weather in several weeks. Southeasterly summit winds will remain under 20 mph until a warm front arriving late today brings slightly higher wind speeds and increasing cloud cover. Precipitation of a wintry mix is forecast to begin tonight but only fall in light amounts. Snow and sleet are forecast to total a trace to 2” by the end of tomorrow, with freezing rain or plain rain possible as well.

SNOWPACK: The few inches of snow which fell this weekend lies on a hard and stubborn two week old wind slab. This older snow also exists at the surface in many places. Today’s weather will be the first significant warming event on our current snowpack structure. Strong springtime solar energy and above freezing temperatures in the ravines will begin to transform our dry upper snowpack, though shady aspects may see minimal affects. Sun exposed aspects, which experienced some warming yesterday and a refreeze overnight, present the possibility for loose wet sluffs in the newer and softer snow today. The effect of warming on a previously unreactive hard slab, which is currently dominant in our upper snowpack, is notoriously tricky to forecast. We don’t expect avalanches from this layer, but it’s worth travelling as if one could occur. Skiers and snowboarders will likely find surface snow become more forgiving today on sunny aspects, though nearly all terrain holds snow allowing decent edge grip and excellent conditions for crampon travel.

The Harvard Cabin will be open all nights this week.

Please Remember:
• 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  7:50 a.m., Tuesday, March 26, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2858