Avalanche Advisory for Wednesday, February 26, 2014

Expires at Midnight

Tuckerman Ravine will have CONSIDERABLE and MODERATE avalanche danger. The Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillmans Highway will have Considerable avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely. Conservative decision making and cautious route finding is essential.  Lobster Claw, Right Gully and the Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.

Huntington Ravine will have CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, Odell, and South Gully have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Conservative decision making and cautious route finding is essential.   All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEMS: Expect new Wind Slab to develop with the forecasted snow squalls today. This will load on top of the wind slabs that have developed since the freezing rain event last week.  Anticipate areas that are most protected from W winds, such as the Lip and Center Bowl in Tuckerman, as well as Central through Odell gullies in Huntington, to be right in the bullseye.   Be suspicious of any new snow that is loaded above the aforementioned crust and perform multiple stability tests as you travel.  Danger ratings posted at Considerable are starting the day one solid step below today’s posting.  They will transition to the Considerable ratings depending on exactly how much squall snow falls as bands move across the region.  It is quite possible that some forecast areas will struggle to reach their rating if we stay on the lower end of the precipitation forecast

WEATHER: Over the past 2 days we have picked up just shy of 3” (7.5cm) on the summit that has been loaded by winds from the W and WNW between 40 and 85mph (68-136kph).  Today, there is a cold front moving our way which will bring a quick hitting system expected to deliver heavy snow squalls at times.  1-3” (2.5-7.5) is anticipated from this event between late morning and dusk, with more upslope snow after dark.  New precipitation will be associated with increased W winds, from the current of 35 (60kph), to 65mph (104kph) this afternoon. This is the dominate weather issue to be paying attention to while in the field.  Exact snowfall intensity, wind velocities, and snow amounts will work together to create the actual level of wind slab problems today.  Watch all three of these factors. A similar squall line is expected tomorrow.

SNOWPACK: As of this morning the dominant feature in the snowpack remains the freezing rain crust. Your primary concern should be focused on new snow above the crust that is not well bonded to this knife hard, and fairly impermeable layer.  The issues will be a mix of older snow from late Friday, new snow from the past 48 hours, and any new snow that develops during today’s squalls. Cold air in place will likely keep new snow densities light making it easy to load with the projected wind speeds.  Expect initial early snow to layer in the deposition of Ravine terrain features more intact due to lighter winds.  This will be followed by denser slab development as new snow crystals become both fragmented and packed in tighter by higher W wind speeds.  This initial lower density snow is the most likely weakness to fracture and fail.  An overrunning avalanche would quite plausibly step down and entrain other layers of slab that we have been discussing over the past several days. Snow beneath the crust also harbors some potential weaknesses, but these will be harder trigger. However, overrunning avalanche load would likely rip out the crust layer particularly in areas of deeper slabs over this lens, like in Tuckerman’s Lip and Center Bowl because of the increased mass.

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 Visitor Center, or the caretakers at Hermit Lake Shelters and Harvard Cabin. Posted 7:10a.m. 2-26-2014. A new advisory will be issued tomorrow.

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

2014-02-26 Print