Avalanche Advisory for Tuesday, February 6, 2018

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch Gullies have Considerable avalanche danger. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. North, Damnation, and Yale Gullies have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features: Evaluate snow and terrain carefully to identify features of concern. 

Tuckerman Ravine has CONSIDERABLE avalanche danger in all forecast areas. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. The Little Headwall is the exception to this rating with open water still preventing it from being a viable ski option.

AVALANCHE PROBLEM: Wind Slab with varying character is our primary avalanche problem. The significant snow since Sunday primarily fell on SW wind which wrapped W and NW while increasing as snowfall tapered off yesterday. Resulting slabs will be relatively firm and stubborn in upper and wind exposed areas, while softer and touchy to a human trigger in lower and more wind sheltered areas. Human triggered avalanches are likely in our steep terrain, and while slabs are spatially variable the resulting avalanche could be large. Lesser winds will continue to transport some snow today though contribute minimally to our avalanche problem. Expect avalanche danger to remain constant through this forecast period as the recently formed wind slabs will gain little, if any, stability today. Continued snowfall this morning will mask surface character of yesterday’s wind slab and make it challenging to discern the type of slab above you, though you may not have visibility. Also remember that wind slab tends to break above you. Safe route finding will be difficult today.

WEATHER: The nearly 10” of new snow since Sunday night was heavily transported by wind yesterday, which had shifted from SW to W by early morning and ultimately blew out of the W to NW around 70-80 MPH for much of the day. Temperatures dropped to the single digits below 0F through yesterday and winds tapered to the current 40’s mph out of the W on the summit. An inch at most of snow fell yesterday, and today should mirror this precipitation with a trace to 2” forecast. Summit temperatures will generally rise today through tomorrow, pushing towards 10F today. Tomorrow, we expect another significant round of snow to impact the area relatively early in the day.

SNOWPACK: Sunday night’s snow fell on moderate SW winds in much of our terrain, creating a relatively soft layer which yesterday’s wind was able to transport readily. Lower deposition zones for snow carried by this wind exhibit a relatively firm and reactive wind slab over the softer storm snow. Though visibility kept observation of our middle and upper start zones to a minimum yesterday, we expect that soft snow does not underlie much of the new wind slab, as wind likely affected all new snow in this terrain. In these more wind affected areas, you would likely find fairly firm new wind slabs which will be more difficult to trigger. While lower in your probability of triggering an avalanche today, these mid and upper slopes hold larger slabs that will be of high consequence if you trigger an avalanche. Prior to the Sunday-Monday storm, the rough melt freeze layer of January had been largely smoothed in avalanche start zones by wind deposited snow. We’re not terribly concerned about instabilities deeper than yesterday’s wind slabs, but keep in mind that they have a largely smooth surface to run on and such avalanches could entrain at least some deeper snow.

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 8:00 a.m., Tuesday, February 6, 2018. A new advisory will be issued tomorrow.

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

2018-02-06