Mar 272015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman and Huntington Ravine have CONSIDERABLE avalanche danger. Careful snowpack and weather evaluation, cautious route-finding and conservative decision making are essential.

 AVALANCHE PROBLEM: We are starting out this morning with a Moderate avalanche danger. 3.1” (7.8cm) of new snow on the summit, with probably just a little less in the Alpine Garden and forecast area, and another trace to 2” (TR-5cm) forecast today, creates the threat of Storm Slab avalanches. A small crown line was visible this morning in Center Bowl which indicates that this new storm snow is cohesive enough to avalanche. That said, a highly skilled user could negotiate this hazard with careful terrain management choices with a careful eye on wind, new snow and the snowpack. Wind Slab may become your greatest concern should you choose to venture into avalanche terrain today. Based on forecast wind speeds, these wind slabs are likely to be smaller than we ordinarily see but will probably form high in our start zones. Either type of avalanche could entrain enough snow to carry you and bury you should you be caught. Remember that while the new snow is “right-side up”, it is resting on a firm bed surface which probably only softened a little bit from yesterday’s brief warming and is refreezing as I write this. This firm surface could make escaping an avalanche with your ski edges or self-arrest tool difficult. If wind does not ramp up today, the Moderate avalanche danger formed by existing Storm Slabs, plus a trace to 2” (TR-5cm) more snow, sluff piles beneath steep terrain and some small wind slabs are what you will have to manage.

WEATHER: 3.1” (7.8 cm) of snow and snow pellets (graupel) were recorded on the summit yesterday afternoon and evening on light winds around 30 mph (50km/h). About 2.4” (6cm) of new snow, starting out as mixed wet particles and freezing rain, fell at Hermit Lake. In all likelihood, 2- 3” of 10% snow is available for transport by the wind into our forecast area from the Alpine Garden area above the Ravines. Both Ravines are moving in and out of the clouds.  Challenging visibility will be the story all day. Temperatures have already dropped to the mid-teens Fahrenheit. NW winds will shift to the West, blowing 15-30 mph (25-50km/h) with gusts to 45 mph (70km/h).

SNOWPACK: Currently the snowpack at Hermit Lake is “punchy” in a few areas. This tells me the crust beneath the new snow is beginning to refreeze following yesterday’s warmup to 44F (7C) at this elevation. Limited visibility this morning only gave us a brief glimpse of Tuckerman Ravine but we did gather some information. The steepest terrain like the narrows of Sluice by the water ice, and the Lip, and probably many other similar areas, appear to have gone through a loose or point release avalanche cycle with debris just beneath the start zones and older, textured surfaces currently visible. The small slab release beneath the ice in Center Bowl showed a crown line approximately 8-10m wide by 10-12 cm thick. It is hard to say whether it released spontaneously or was triggered by a sluff off of the ice bulge above. In any case, the slab character is not typical of other areas we’ve seen this morning. The snow at Hermit Lake is only barely cohesive, and remarkably dry…it takes some effort to make a marginally solid snowball.

Tomorrow will defy expectations for spring conditions again. Expect similar conditions as today so remember to bring your good judgment, avalanche rescue gear and well-honed decision making skills if you are headed this way for the weekend. And remember that a back-up plan to skiing or climbing in steep avalanche terrain should be a desirable alternative that is acceptable to the group.

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 the Harvard Cabin.
  • Posted 8:49 a.m. Friday, March 27, 2015. A new advisory will be issued tomorrow.

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

2015-03-27 print version

Mar 262015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman and Huntington Ravine have MODERATE avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible in all forecast areas.  Evaluate weather, snow and terrain carefully to identify features of concern. Heightened avalanche conditions will develop on specific terrain features later today.

Mixed precipitation is expected to get started in the afternoon which will push us higher into the above ratings this afternoon. The ratings above most accurately reflect the daytime recreational period. Anticipate avalanche danger to increase, moving towards Considerable near sundown and more certainly in that rating after dark.

AVALANCHE PROBLEM: Existing stability is generally good to very good in most of the forecast area either because the upper snowpack is wind packed or wind scoured, or because it was exposed to strong solar heating yesterday. Some strong lee areas, like the Chute and the left side of Center Bowl as well as other lee pockets, harbor softer slabs. These softer slabs create the potential for Wet Slab avalanches later today as mixed precipitation falls. Wind Slabs may also develop later in the day. The degree to which these wind slabs will be problematic depends upon the type and timing of the precipitation’s changeover to snow.

WEATHER: The 1/3” of new snow yesterday evening did little to impact our stability. More precipitation is forecast for the afternoon with 1/4″ of water equivalent by dark and another 1/2″ or so through the night. The good news is that it will be getting colder with mixed precipitation on the summits turning to increasingly lighter snow overnight. The bad news is there is some chance for rain, in addition to freezing rain, sleet and snow, in our avalanche forecast area for a period this afternoon. Though not a tremendous amount of precipitation, it may be enough to weaken some existing softer surface slabs or penetrate thinner slabs. The type of precipitation is a wild card due to the position of the melt/freeze line within our forecast area.  Keep a close eye on temperature and incoming precipitation since they will directly impact stability today. As mentioned above, snow this afternoon and evening will increase and grow less dense as the cold front arrives with 2-4” expected to fall on diminishing winds overnight. Favorable conditions for upslope generated snow showers are forecast tomorrow with west winds potentially in the light range. Expect a new wind slab problem tomorrow and a return to wintry weather.

SNOWPACK: Generally firm or hard snow predominates in our terrain due the freeze/thaw cycle that started on Tuesday. Though summit temperatures that day never climbed to the mid-teens, the strong sunshine and dead calm wind in the forecast area allowed significant warming, even in shaded areas. Yesterday, it was apparent that south facing ice climbs in Huntington took a beating and slopes in Tuckerman developed peel away corn snow. Cooler temperatures overnight have no doubt hardened these aspects but the damage to ice features remains. Expect a hard surface requiring crampons and an ice axe in most areas today.  As a reminder, the warm temperatures over the past two days have not created a stable, isothermal spring snowpack.  Be wary of weak layers buried well down in the snowpack particularly in slightly lower elevation, lower angled terrain outside our forecast area.  Deeper weak layers in our terrain also exist but will most likely require more than today’s precipitation to activate.

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 the Harvard Cabin.
  • Posted 8:26 a.m. Thursday, March 26, 2015. A new advisory will be issued tomorrow.

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

2015-03-26 print friendly