Avalanche Advisory for Thursday, February 12, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable and Moderate avalanche danger. Sluice, Lip, Center Bowl and Chute will rise to a Considerable rating today. A Considerable rating means natural avalanches are possible and human triggered avalanches are likely. Careful snowpack and weather evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas in Tuckerman have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible in Lobster Claw, Right Gully, Left Gully, Hillman’s Highway and the Lower Snowfields. Natural and human-triggered avalanches are unlikely in the Little Headwall which is posted at Low.

Huntington Ravine has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow, weather and terrain carefully.

AVALANCHE PROBLEM: Wind Slabs remaining from loading on Monday, Tuesday night, as well as new slab created late today with additional snowfall, is the main avalanche problem.  Soft slab development from light S winds on Monday and higher NW winds on Tuesday night continue to hold instability issues.  This was confirmed by field work yesterday afternoon.  Aspects facing away from direct solar effect, even slightly, are retaining their snappy shooting cracks.  On aspects facing towards the S and SE, slabs went through two solar heating consolidation events on Tuesday and Wednesday which has helped make these slopes more stable.  New slab development is expected later today creating new thin slabs on aspects with an E facing component due to a building W wind.

WEATHER: The amount of snow, wind velocity and timing of today’s frontal passage is crucial to stability concerns today. If we receive the upper end of the 1-3” (2.5-7.5cm) forecast today, with higher gusts of 45 mph (70 km/h), then we will reach the upper end of the ratings this afternoon. These westerly winds will have more snow to move into Tuckerman, but less into Huntington, due to the smaller alpine areas above. The MWOBS forecast indicates W winds of only 20-30 mph which would have little effect on our ratings even with 1-3” of new snow. That said, expect colder conditions (dropping to 5F or so) with flat light making accurate field assessments increasingly challenging. An early start and finish will be in your best interest and leave you with only pre-existing stability concerns from earlier this week to deal with.

SNOWPACK: As we move further from the low density storm over last weekend, loading events on Tuesday, and two windows of solar heating over the past 48 hours, our snowpack variability has been increasing.  When conceptualizing the differences out there it seems like chaos, but there is some rhyme and reason for a very diverse variable snowpack.  We’ll try to boil it down to the key data. Very low density snow that fell over the weekend into Monday came in on low S winds, roughly between 20-30 mph.  Dry loose sluffing occurred Sunday afternoon and Monday on a variety of aspects.  Skiers found very soft slabs that were barely perceptible from loose unconsolidated snow on Monday and Tuesday.  On Tuesday the sun dominated the sky, again with low wind.  This cooked S facing slopes enough that roller balls and some wet sluffing occurred, testing some of the deep slabs on those aspects.  Due to its steepness and slick blue ice this was most prevalent in Huntington.  Tuesday afternoon and evening 60 mph NW winds loaded snow into high start zones, mostly over these heated slopes.  This same heating happened again yesterday, while areas in the shade remained cold and snappy.  Chris went into the S faces yesterday finding the low density snow from Monday-Tuesday was now moist while Jeff shivered in the shade of the Chute and Left Gully.  Chris found issues leading to wet sluff potential while Jeff backed off in places due to shooting cracks in 4F softslab over an unconsolidated snow weak layer.  We agreed this was likely across the entire south half of the Tuckerman Bowl, from the Center Headwall to Left gully.  We mention all of this to give some history why a skier traversing from Right Gully to Left Gully will find very different stability as they move.  Expect stability to change quickly so constant evaluation is critical.  The bottom line is S faces have more stability than E and N aspects this morning.  As the day progresses 1-3″ (2.5-7.5cm) of snow is forecasted to fall on a light W wind.  Late in the day wind velocity will increase causing some concern for natural avalanche potential later.  We believe this may occur quite late so Moderate danger will be appropriate for the majority of the day.  Planning to be off of slopes with an East facing component later this afternoon would be prudent.  If 3″ (7.5cm) fall and we get the NWS forecasted gusts to 45mph, expect the forecasted areas described as Considerable to reach the definition of natural avalanches being possible during daylight hours.

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 8:40 a.m. February 12, 2015. A new advisory will be issued tomorrow.

Christopher Joosen/Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2015-02-12