Avalanche Forecast for Saturday, February 15, 2020
This information was published 02/15/2020 at 7:00 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
The threat of natural avalanches passed when wind loading ceased late yesterday. Human triggered avalanches remain possible today with the possibility of a very large avalanche in Tuckerman Ravine. Don’t let firm, smooth but hollow snow trick you into thinking things are stable. While these slabs are likely to be stubborn, bear in mind these considerations:
Heavy wind loading occurred through the day yesterday. This is a classic “red flag”.
Very cold temperatures in the past 36 hours have slowed settlement and bonding.
Thin spots are often trigger points that can be found along the edges of an otherwise thick slab. A crack could bring a slope down on you if you are in the wrong place.
The avalanche danger today is MODERATE in wind loaded terrain. Assess snow and terrain carefully and beware of others above you and your position below steep, open slopes and gullies.
Yesterday, wind from the northwest remained solidly in the 60’s mph until around dark when it finally shut down. Ambient temperatures were in the mid-teens below zero until that time also. Check out this Instagram video of yesterday’s text-book wind loading scenario.
Today, temperatures have warmed to around 0F on the summit with an inversion keeping temps in nearby valleys at -17F. Southwest flow will bring warmer air today and some high clouds later with a high of 11F on the summit. There should be good visibility through the daylight hours though snow and fog will develop overnight.
Tomorrow, we may have an inch of snow available for increasing west and WSW winds to work with overnight. Temps will warm to the low teens on the summit but strong winds will remain through mid-day and diminish to the 30-40mph range.
Primary Avalanche Problem – Wind Slab
Wind slabs remain a threat in predominantly east facing terrain today. Though some areas, such as the higher elevation northern gullies in Huntington Ravine, are largely scoured or wind packed, other, more sheltered areas like Sluice and the Lip in Tuckerman Ravine have thick, smooth and continuous hard slabs over a softer layer of snow deposited earlier this week. Widely variable thicknesses of these layers above the most recent ice crust means that you stand a decent chance of passing over a thin, weak spot in a slab and trigger an avalanche. You’ll be able to find softer, more reactive but smaller wind slabs in wind sheltered areas.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
This is the kind of day that makes me wish for a further break out of danger ratings. If you are climber, you know that difficulty ratings are often assigned a danger rating to indicate the level of protection available and consequence of a fall. Many people can lead a 5.10 comfortably but would avoid a 5.10R or X like the plague, for good reason. A mistake on a 5.10X could mean serious injury or death. Consider today’s MODERATE rating a 5.10R/X until you determine otherwise through careful assessment. A few places harbor serious avalanche concerns while others contain firm and stubborn slabs that would require a huge trigger to crack and fail. Observations were limited yesterday by dangerous, ongoing wind loading but shooting cracks and sizable slabs on expansive and connected slopes turned experienced skiers and avalanche practitioners around. Bring your A-game today and consider your exposure to overhead hazard. There are plenty of lower consequence options around, you’ll just need to be creative and careful to enjoy them.
Safe travel in avalanche terrain requires training and experience. This forecast 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.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 02/15/2020 at 7:00 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest
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