Avalanche Advisory for Sunday, April 9, 2017

This advisory expires at Midnight.

Huntington Ravine has MODERATE and LOW avalanche danger. North, Damnation, Yale and Central Gully have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely.

 Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely in Sluice, Lip and Center Bowl. Careful snowpack evaluation, cautious route finding, and conservative decision-making are essential. All other forecast areas except the Little Headwall have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Open water and thin snowbridges exist in spots in the Little Headwall which has Low avalanche danger.

 AVALANCHE PROBLEM: Wind slabs developed yesterday due to high northwest winds and five to six inches of snow which fell during the day and five to six inches which fell the night before. These wind slabs are firm and likely to be stubborn this morning but will lose strength as sun and warm temperatures warm and weaken them. Areas rated Considerable in Tuckerman Ravine are likely to produce human-triggered loose-wet avalanches and possibly wet slab avalanches later today. Northern gullies along with Central will have similar avalanche problems, though avalanches are likely to be smaller. Protect yourself if climbing into these wind slabs or avoid them if you can. Today may feel like spring but our snowpack is not the stable, springtime snowpack more typical of this time of year.

 WEATHER: With temperatures in the teens, sustained winds exceeding 80 mph, and a summit snowfall total of 6.6 inches, yesterday’s weather brought winter back to Mount Washington. This morning, milder conditions are already returning with decreasing wind and a current temperature at Hermit Lake of 27F. Summit wind will decrease to approximately 30 mph by mid-afternoon, with temperature rising to 37F. Partial cloud cover may appear late this afternoon, but it’s shaping up to be a largely sunny day.

SNOWPACK: Over the past 48 hours, we’ve seen rain and warm temperatures give way to cold, windy, and snowy weather, with a sunny spring day well above freezing temperatures forecast today. A storm snow total of approximately 10-12” has been consistently transported by strong northwest wind since early yesterday. The wet surface snow prevalent prior to this storm has refrozen to a supportable crust that is several inches thick. Also of note, our wet snow Thursday and Friday produced heavy rollerball action and some loose wet avalanche activity, particularly in the lower half of N and NE facing forecast areas. This mess of refrozen snow has seen both scouring and deposition by wind over the past 24 hours. Generally, upper start zones are currently loaded with a relatively firm wind slab and lower portions of forecast areas are scoured to the refrozen snow mentioned above.  Heaviest loading, creating thick slabs, is in areas lee to the recent NW wind direction. Notice that these wind slabs exist in areas that the refrozen layer is smoothest. Many areas displaying significant rollerballs having were also scoured by wind. In short, don’t expect texture in the melt/freeze layer to be a much of a stabilizing factor. As temperatures approach or exceed 40F in the ravines today, sun warming the newly formed slabs will increase sensitivity to a human trigger. Naturally, these slabs will also provide the best skiing surface, so be sure to temper your desire for quality turns with your critical decision making abilities. Mixed conditions with likely human triggered avalanches will make for a day that is far from a classic spring Tuckerman Ravine experience.

The Harvard Cabin is closed for the season. We will continue posting advisories there as long as it is logistically feasible or until the ice melts out. Be sure to check the date of the advisory when you read it!

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 caretaker at Hermit Lake Shelters.

Posted  8:00 a.m., Sunday, April 9, 2017. A new advisory will be issued tomorrow.

Frank Carus/Ryan Matz, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856