Avalanche Advisory for Thursday, March 29, 2018

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

AVALANCHE PROBLEM: Temperatures will rise well above freezing today. So far, heating has been limited to the sunniest slopes and even then, wind and cool temperatures has limited heating to the surface. Today’s weather and snowpack trend is similar to the day a few years ago when a very large human triggered avalanche occurred on the summit cone. The warm temperatures that melt bonds between grains in the snowpack and create great skiing and riding conditions also melt bonds deeper in the snowpack. The first strong warming trend tests the strength of the snowpack, and in our case today, creates a low probability, high consequence avalanche problem. Natural and human-triggered avalanches are unlikely in most of our terrain but the threat of a large, hard slab makes it advisable to ski or ride a slope one at a time and to continue to carry your avalanche rescue gear. Large convexities or thin spots would be the most likely locations to trigger this type of avalanche. Wet loose avalanches could also occur in areas with strong solar gain or in the limited areas where soft snow remains. Low avalanche danger does not mean no avalanche danger!

WEATHER: A strong inversion this morning has valley locations slightly cooler than the summit which has already reached 30F. Tuesday night brought a trace amount of mixed precipitation to the mountain. Today looks clear and fairly calm though SW flow will bring clouds and eventually rain later this afternoon and evening. It looks as if these clouds won’t lower to become summit fog until nighttime though high clouds already developing this morning may reduce solar gain a bit this afternoon as they thicken. Temperatures should reach to the mid or high 30’s with 20-35 mph SW wind in the afternoon. Almost an inch of rain is forecast overnight and will further test our snowpack into tomorrow. Percolating rain in the snowpack will likely raise our avalanche concerns further tomorrow. 

SNOWPACK: The hard, icy melt-freeze crust that exists deep in the snowpack, beneath the firm wind slabs which developed March 17th, is one of the layers that will be a player in avalanche activity that occurs over the next couple of days. Rapid warming is one of the classic red flags signaling avalanche danger, along with heavy precipitation of any variety. The next 48 hours will bring changes to the snowpack which will ultimately reduce our avalanche concerns to the surface. Until then, we will continue to have the potential for a larger hard slab avalanche.

The Sherburne Ski Trail has good coverage top to bottom and should soften through the day. The usual scoured areas may start to reveal some rocks.

Check our Instagram page, linked on our website, for conditions photos and additional updates. You don’t need an account to view our posts!

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  7:45 a.m., Thursday, March 29, 2018. A new advisory will be issued tomorrow.

Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2858