Avalanche Advisory for Tuesday, April 4, 2017

This avalanche advisory expires at Midnight.

Huntington and Tuckerman Ravine will have CONSIDERABLE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision-making will be essential. The only exception to this is the Little Headwall which has Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Today, Wind Slab will form on north and east-facing aspects. This hazard will increase through the day as snowfall accumulates and wind speed increases. While north-facing slopes will see the greatest amount of loading due to being directly in the lee of wind, east-facing slopes contain the largest snowfields and have the potential to produce the largest avalanche. While south-facing slopes will see little loading, today’s snow will become denser creating an upside down snowpack that could become reactive to human triggers. While several slopes avalanched over the weekend, many did not. The potential for wind slab today stepping down into the slab that formed over the weekend is possible. Be aware of the possibility of avalanches becoming large today.

WEATHER: Yesterday, wind diminished from 50mph in the morning to under 10mph as the direction shifted from the NW to the S. While this occurred, temperatures increased from the low teens Fahrenheit on the Summit to a maximum of 27F just before midnight. At Hermit Lake, the maximum temperature recorded yesterday was almost 43F. Overnight, clouds developed as low pressure approached. Currently at Hermit Lake it is snowing at a rate of 1cm per hour (S1) with a temperature of 28F. The Summit is recording winds from the SE at 48mph and a temperature of 22F. Today, wind speeds will increase slightly midday to 60mph and then decrease again to the 35-50mph range, remaining SE for the day. Snow will likely be heavy this morning with possibly 4” falling by early afternoon. A possible lull in the snow mid-afternoon will be followed by another round of heavy snowfall. Increasing temperature in the afternoon will make this snow heavier, possibly introducing sleet. All told, by midnight, it seems likely 9” of snow may arrive with a water equivalent of 1”.

SNOWPACK: The bed surface of the snowpack is the melt/freeze crust from last week. This crust has been tested by numerous avalanches and is solidly frozen. On top of this, approximately 12” of snow fell Friday into Saturday. This was followed by temperatures in the mid-teens and 20sF on Sunday and Monday with partially clear skies Sunday and clear skies Monday. South facing aspects received ample solar gain, with snow becoming saturated down to roughly 20cm. Cold temperatures last night froze the top10cm of this wet snow while the 10cm of wet snow beneath is still in the process of refreezing. Moving across east-facing slopes, these saw sun, but not to the same degree. The wet layer of snow is closer to only 10cm thick and seems to be completely refrozen. North facing slopes contain a mix of very thin sun crust and dry snow. These slopes, including Left Gully, Hillman’s, Odell, South Gully and Escape Hatch, will likely load significantly today from new snow transported on SE winds. With an increase in wind midday and snow increasing in density later in the day, expect to find an upside-down snowpack forming on north-facing slopes. While not forecast for, the steeper gullies on the Boott Spur Ridge will load significantly today as well. This is worth noting as many of them runout into Hillman’s Highway. East and south-facing slopes will see less loading, but with snowfall being heavy at times and becoming denser falling, the same upside-down snowpack will form.


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 Harvard Cabin.

Posted  8:30a.m., Tuesday, April 4, 2017. A new advisory will be issued tomorrow.

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