Mar 282015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable, Moderate and Low avalanche danger. The Chute has Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. The Sluice, Lip, Center Bowl, Left Gully, Hillman’s Highway and Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Lobster Claw, Right Gully, and Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

All forecast areas of Huntington Ravine have Moderate avalanche danger. Natural are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEM: Wind Slab and Storm Slab are the primary concerns today with Dry Loose avalanches also on the list. 3.5” (8cm) of new snow in the past 2 days has created a variety of soft slabs in our terrain. Due to the low wind speeds, the new snow is piling up beneath steeper terrain and forming slabs just cohesive enough to create potentially dangerous slabs. Small avalanches could turn larger by entraining the surprising amount of low density snow laying around.

WEATHER: The Low pressure trough continues to feed clouds and moisture into the area. 1-3” (2.5 – 7.5cm) of new snow is expected today on very lights winds shifting to the North. Expect flat light at best and possibly denser fog to create some challenges for navigating and keeping eyes on the skier. It is likely that the overcast skies above the summit fog will limit incoming solar heating on southern aspects today, unlike yesterday.  The height and intensity of the spring sun is a factor this time of year and could conceivably have a positive effect on stability on these aspects again today. Quite a bit of warming occurred yesterday, in spite of the dense fog.

SNOWPACK: Currently, very low density snow is sluffing off steep terrain and contributed to these slabs. In Tuckerman, Chute holds the greatest amount of soft slab, with boot-top and deeper snow in and above the choke. The narrows of Left, as well as near and above the fork of Hillman’s, were also a concern yesterday. Cracking and increasingly deep snow lead experienced parties to turn around in both locations. 1” (2.5cm) of new snow on even lighter winds last night plus 1-3” more today will contribute to this problem. It is impressive how this paltry amount of snow piles up beneath steep terrain like cliff bands, ice bulges and sidewalls of gullies. Huntington is a mixed bag of Moderate. Greenhouse warming yesterday contributed to stability on south facing aspects so expect more stability concerns from Central to Escape Hatch with more stability from Yale to North.

Field time in Tuckerman confirmed that we still have a dynamic snowpack. Despite cold air temperatures, greenhousing conditions over the past several days have begun to drive heat into the upper 30-40 cm of snow, though the temperatures beneath are far from isothermal. Stability tests yesterday confirmed the new snow was well bonded to the hard surfaces but was slabbing up due to either surface heat gain, light wind effect or sluffing. The older bed surface was just barely negotiable without crampons (2-3cm boot penetration) yesterday but has refrozen more solidly this morning. Expect a slippery, dust on crust surface especially on southerly aspects unless heating occurs. Deeper in the snowpack pooled graupel and a thick, decomposing melt/freeze crust failed cleanly but are well bridged and not much of a concern for the time being.

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 8:23 a.m. Saturday, March 28, 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

2015-03-28

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