Avalanche Advisory for Friday, April 20, 2018

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central Gully has Considerable avalanche danger. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. The Little Headwall is no longer forecast due to open holes in the snowpack and is not recommended as an exit from the Bowl.

AVALANCHE PROBLEM: Six inches of new snow overnight arriving on increasing NW wind makes wind slab our avalanche concern today. No visibility this morning adds a degree of uncertainty to today’s forecast. We expect the snow to struggle to adhere to the ice crust which will act as today’s bed surface. This highlights a key characteristic about today’s avalanche problem; wind slab will likely be touchy to human triggers. In Moderate rated areas, the combination of wind and the slick bed surface may allow scouring to take place leaving areas of bed surface exposed. Considerable rated slopes, those in the lee of our fetch, should hold much larger areas of wind slab with limited to no old surface exposed. The potential for large avalanches exist in these areas with the possibility of natural avalanches due to continued loading through the day. The floor of Tuckerman Ravine today will be avalanche terrain as we have seen avalanches run far this year on well-developed slide paths. The hard bed surface will demand the use of crampons and an ice axe for those choosing to travel in avalanche terrain.

WEATHER: Low pressure centered over Nova Scotia will continue to send bands of winter weather to Mount Washington today. After a midday lull yesterday in wind speed combined with a spike in temperature to the mid-20s on the summit, snowfall began along with an increase in wind and a drop in temperature. Winds bottomed out at 5mph around noon yesterday and by midnight were above 40mph. As of this morning, the summit recorded 5.2” of snow while just under 6” fell at Hermit Lake. Today, temperatures will remain in the 20’s F in avalanche terrain with the summit reaching the upper teens. Winds should stay in the 40-55mph range from the NW. Snow is likely; 0.25” of SWE is forecast to arrive by this evening which could amount to another 2+” of snow. Wind and temperatures tonight should remain similar to today with another possible 2” of snow by tomorrow morning.

SNOWPACK: Over the past week, 10” of mixed precipitation arrived with a SWE of 3”. This was followed by cold temperatures that allowed a thick ice crust to form. On Wednesday, this crust was 4cm thick in places with moist snow beneath. With continued cold Thursday and last night, this crust will remain thick and strong, limiting avalanche concerns to the surface wind slab. We expect the new wind slab to vary in size from small to large depending on terrain and aspect. The uncertainty of wind slab size today comes from a combination of weather and snowpack factors compounded by no visibility. This same visibility challenge will make safe travel decision difficult today, as seeing avalanche start zones will be difficult. Days like today, which have a degree of uncertainty, are best for choosing low consequence terrain. The Sherburne will ski well today with top to bottom coverage.

Bear tracks were seen around the Fire Road and Tuckerman Ravine Trail. Please use the bear boxes and keep your camp clean if staying overnight at Hermit Lake. The Harvard Cabin is closed with no camping allowed anywhere on the east side of Mount Washington except at Hermit Lake Shelters or adjacent tentsites.

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.
• Posted  8:00 a.m., Friday, April 20, 2018. 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

2018-04-20

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Hermit Lake

April 20, 2018 at 6:57 am
Air Temperature: -6.5 C
Sky Condition: Overcast
Precip Type: Snow
24H Snow Total: 15 CM
Density: 13%
Snow Temp Surface: -5.5 C
Snow Temp -10cm: -4.5 C
Snow Temp -20cm: -2.5 C
Height of Snowpack:178 CM

Hermit Lake

April 19, 2018 at 6:05 pm
Air Temperature: -4.5 C
Sky Condition: Overcast
Precip Type: Snow
24H Snow Total: Trace
Snow Temp Surface: -3.0 C
Snow Temp -10cm: -2.0 C
Snow Temp -20cm: -1.5 C
Height of Snowpack:163 CM